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LIBRARY 

.OF   THE 

DENTAL  DEPARTMENT, 

UNIVERSITY  OF  CALIFORNIA. 

This  book  must  be  returned  within  four  days.     Fine,  five 
cents  each  day  for  further  detention. 

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CARPENTER'S 


ELEMENTS  OF   PHYSIOLOGY, 


ELEMENTS 


PHYSIOLOGY, 


INCLUDING 


PHYSIOLOGICAL    ANATOMY. 


WILLIAM  B.  CARPENTER,  M.D.,  F.R.S.,  F.G.S., 

EXAMINER  IX  PHYSIOLOaT  AND  COMPARATIVE  ANATOMT  IN  TOE  UNIVERSITY  OF  LONDON;   AND  AUTHOR  OP 

"THE  PRINCIPLES  OF  HUMAN  PHYSIOLOGY,"  AND  "THE  PRINCIPLES  OF  GENERAL 

AND  COMPARATIVE  PHYSIOLOGY,"  ETC. 


SECOND  AMERICAN, 

FROM    A    NEW    AND    REVISED    LONDON    EDITION. 

WITH  ONE  HUNDRED  AND  NINETY  ILLUSTRATIONS. 


PHILADELPHIA: 

BLANCHARD    AND    LEA. 

1851. 


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C.    SHERMAN,    PRINTER. 


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AMERICAN  PUBLISHERS'  ADVERTISEMENT. 


The  present  volume  has  been  printed  simultaneously  with  the  Second 
London  Edition.  The  numerous  alterations  which  Dr.  Carpenter  has 
introduced,  and  the  thorough  manner  in  which  he  has  revised  every 
portion  of  it,  have  rendered  unnecessary  any  notes  or  additions.  The 
efforts  of  the  publishers  have,  therefore,  been  directed  towards  obtaining 
a  correct  reprint,  to  accomplish  which,  its  passage  through  the  press 
has  been  supervised  by  Dr.  F.  G.  -Smith,  Lecturer  on  Physiology  in  the 
Philadelphia  Association  for  Medical  Instruction.  It  is,  therefore,  con- 
fidently presented  to  the  Profession,  as  in  every  way  worthy  of  the 
high  reputation  which  it  has  obtained  as  an  elementary  text-book. 

Philadelphia,  October,  1851. 


PREFACE 


The  present  volume  owes  its  origin  to  a  desire  on  the  part  of  the 
Publisher,  that  an  elementary  treatise  on  Physiology  should  be  added 
to  the  series  of  »admirable  Students'  Manuals,  on  the  various  depart- 
ments of  Medical  Science,  which  he  had  previously  issued. 

In  carrying  this  desire  into  execution,  the  Author  has  endeavoured 
to  avoid  inflicting  upon  the  class  for  whose  use  the  Treatise  is  especially 
intended,  the  injury  of  placing  in  their  hands  such  a  superficial  and 
imperfect  sketch  of  the  science,  as,  whilst  affording  them  but  a  limited 
amount  of  knowledge  of  its  facts,  should  leave  them  very  ill-informed 
as  to  its  general  doctrines.  His  object  has  rather  been  to  convey  to 
the  Student  as  clear  an  idea  as  possible  of  those  Principles  of  Physiology 
which  are  based  on  the  broadest  and  most  satisfactory  foundation,  and 
to  point  out  the  mode  in  which  these  principles  are  applied  to  the 
explanation  of  the  .  phenomena  presented  by  the  living  actions  of  the 
Human  body.  In  this  manner  has  the  Author  desired  to  prepare  him 
for  that  more  detailed  study  of  the  latter,  which  becomes  necessary  when 
Physiology  is  pursued  (as  it  ought  to  be)  in  connexion  with  the  changes 
produced  in  the  living  body  by  Morbific  and  Remedial  Agents,  and  is 
thus  taken  as  a  guide  in  the  study  of  the  causes,  prevention,  and  treat- 
ment of  Disease — which  should  be  the  primary  object  of  attention  with 
every  one  who  undertakes  the  Practice  of  his  Profession. 

Although  this  Manual  combines  in  some  degree  the  scope  of  the 
Author's  "  Principles  of  Physiology,  General  and  Comparative,"  and 
of  his  "Principles  of  Human  Physiology,"  yet  it  cannot  be  regarded 
as  a  mere  abridgment  of  them,  having  been  written  for  the  most  part 
with  very  little  reference  to  them,  and  with  every  desire  to  make  it 
complete  in  itself.  As  the  matter  of  which  these  volumes  are  composed 
is  itself  condensed  to  the  utmost  practicable  degree,  it  is  manifestly 
impossible  that  the  present  Manual  should  contain  more  than  a  mere* 
outline  of  the  subjects  of  which  they  treat.     To  them,  therefore,  he 


Vlll  PREFACE. 

would  refer  such  of  its  readers,  as  may  desire  further  information  upon 
various  topics  which  are  here  only  slightly  touched  upon ;  and  in  them, 
also,  will  be  found  references  to  various  original  authorities,  the  intro- 
duction of  which  would  be  incompatible  with  the  limited  scope  of  a 
treatise  like  the  present. 

The  Author  has  only  to  add,  that  he  feels  most  grateful  for  the  kind 
appreciation  which  this  Manual  has  experienced  ;  and  that  in  the  prepa- 
ration of  the  present  Edition,  he  has  used  his  best  endeavours  to  render 
it  still  more  worthy  of  a  favourable  reception.  The  whole  treatise  has 
been  subjected  to  a  most  careful  revision ;  many  statements  which  the 
advance  of  science  has  shown  to  be  doubtful  or  erroneous,  have  been 
omitted  or  corrected;  and  a  considerable  amount  of, new  matter  has 
been  introduced.  Of  the  First,  Eleventh,  and  Twelfth  Chapters,  more 
especially,  a  considerable  proportion  has  been  entirely  rewritten ;  and 
the  Author  ventures  to  believe  that  the  doctrines  which  they  contain  will 
enable  such  as  may  master  them  to  obtain  a  clearer  comprehension 
of  the  facts  of  Physiological  Science,  than  they  could  previously  have 
acquired. 

Regent's  Park,  London, 
September,  1851. 


TABLE  OF  CONTENTS. 


BOOK  I. 

GENERAL   PHYSIOLOGY. 


I.  On  the  natuke  and  objects  of  the  Science  of  Physiology 

1.  General  Characters  of  Organized  Structures 

2.  Distinctive  Characters  of  Vital  Actions 

3.  Of  the  Forces  concerned  in  the  production  of  Vital  Phenomena 

4.  Of  Degeneration  and  Death  ..... 

5.  General  Summary  ...... 

II.  Of  the  Exteknal  Conditions  of  Vital  Activity  . 

1.  Of  light,  as  a  Condition  of  Vital  Activity 

2.  Of  Heat,  as  a  Condition  of  Vital  Activity 

3.  Of  Electricity,  as  a  Condition  of  Vital  Activity  . 

4.  Of  Moisture,  as  a  Condition  of  Vital  Activity 

III.  Of  the  Elementary  Parts  of  Animal  Structures     . 

1.  Of  the  Primary  Components  of  the  Animal  Fabric  . 


PAQE. 

17 

18 
25 
44 
53 
56 

68 

61 
71 
94 
97 

105 

107 
119 
127 


2.  Of  the  Simple  Fibrous  Tissues 

3.  Of  the  Basement  or  Primary  Membrane 

4.  Of  Simple  Isolated  Cells,  employed  in  the  Organic  Functions    .  130 

5.  Of  cells  connected  together,  as  permanent  constituents  of  the  Tissues      154 

6.  Of  Cells  coalesced  into  Tubes,  with  Secondary  Deposit .  .  196 


BOOK  II. 

,      SPECIAL   PHYSIOLOGY. 

IV.  Of  Food,  and  the  Digestive  Process        .....  286 

1.  Sources  of  the  Demand  for  Aliment        ....  286 

2.  Of  the  Digestive  Apparatus,  and  its  Actions  in  general       .            .  252 

3.  Of  the  Movements  of  the  Alimentary  Canal        .             .             .  257 

4.  Of  the  Secretions  poured  into  the  Alimentary  Canal,  and  of  the 

Changes  which  they  eflFect  in  its  contents               .            .            .  264 

5.  Of  Hunger,  Satiety,  and  Thirst  .  .  .  .274 

V.  Of  Absorption  and  Sanguification           .....  277 

1.  Of  Absorption  from  the  Digestive  Cavity            .            .            .  277 

2.  Of  the  Passage  of  Chyle  along  the  Lacteals,  and  its  admixture 

with  the  Lymph  collected  from  the  General  System           .             .  281 
8.  Of  the  Spleen,  and  other  Glandular  appendages  to  the  Lymphatic 

System               .......  286 

4.  Of  the  Composition  and  properties  of  the  Chyle  and  Lymph            .  292 

5.  Of  Absorption  from  the  External  and  Pulmonary  Surfaces        .  296 

6.  Of  the  Composition  and  Properties  of  the  Blood      .  .  .297 


TABLE    OF    CONTENTS. 


CHAPTER. 

VI.  Of  the  Circulation  of  the  Blood        .... 

1.  Nature  and  Objects  of  the  Circulation  of  Nutrient  Fluid 

2.  Diflferent  forms  of  the  Circulating  Apparatus     . 

3.  Action  of  the  Heart   .... 
•    4.  Movement  of  the  Blood  in  the  Arteries  . 

5.  Movement  of  the  Blood  in  the  Capillaries     . 

6.  Movement  of  Blood  in  the  Veins 

VII.  Op  Nutrition  ..... 

1.  Selecting  Power  of  Individual  Parts 

2.  Varying  Activity  of  the  Nutritive  Processes 

3.  Of  Death,  or  Cessation  of  Nutrition 

4.  Disordered  Conditions  of  the  Nutritive  Processes 

VIII.  Of  Kespiration  ...... 

1.  Essential  Nature  and  Conditions  of  the  Respiratory  Process 

2.  Different  forms  of  the  Respiratory  apparatus  in  the  lower  Animals 

3.  Mechanism  of  Respiration  in  Mammalia,  and  in  Man    . 

4.  Chemical  Phenomena  of  Respiration 

5.  Effects  of  Insufficiency,  or  Suspension,  of  the  Aerating  Process 

IX.  Of  Secretion   .  .  .  . 

1.  Of  the  Secreting  process  in  general,  and  of  the  Instruments  by 

which  it  is  effected 

2.  Of  the  Liver  and  the  Bile 

3.  Of  the  Kidneys,  and  the  Urine 

4.  Of  the  Cutaneous  and  Intestinal  Glandulae 

5.  General  Summary  of  the  Excreting  Processes 

X.  Of  the  Development  of  Light,  Heat,  and  Electricity,  in  the  Animal 
Body  ........ 

XL  Generation  and  Development 

1.  General  View  of  the  Nature  of  the  Process 

2.  Action  of  the  Male     . 

3.  Action  of  the  Female 

XII.  Of  the  Nervous  System     . 

1.  General  view  of  the  operations,  of  which  the  Nervous  System  is 

the  Instrument  ...... 

2.  Comparative  Structure  and  Actions  of  the  Nervous  System 

3.  Functions  of  the  Spinal  Cord  and  its  Nerves 

4.  Functions  of  the  Medulla  Oblongata 

5.  Functions  of  the  Sensory  Ganglia 

6.  Functions  of  the  Cerebellum 
9.  Functions  of  the  Cerebrum 
8.  Functions  of  the  Sympathetic  System 

XIII.  Of  Sensation,  General  and  Special  . 

1.  Of  Sensation  in  general 

2.  Of  the  Sense  of  Touch     . 

3.  Of  the  Sense  of  Taste 

4.  Of  the  Sense  of  Smell      .  .  : 
6.  Of  the  Sense  of  Hearing 
6.  Of  the  Sense  of  Sight      . 

XIV.  Of  the  Voice  and  Speech 


LIST  OF  WOOD  ENGRAVINGS. 


1.  Simple  isolated  Cells,  containing  reproductive  molecules 

2.  Fibrous  structure  of  exudation-membrane  ;  after  Gerber 

3.  Fibrous  membrane  lining  egg-shell  (original) 

4.  White  fibrous  tissue  of  areolar  tissue  and  tendon ;  after  Gerber   . 

5.  White  fibrous  tissue  of  ligament ;  after  Gerber 

6.  Yellow  fibrous  tissue  of  ligamentum  nuchee  ;  after  Gerber 

7.  Development  of  fibres  from  cells ;  after  Lebert 

8.  Ideal  Section  of  a  Joint       ...... 

y.  Capillary  vessels  of  Skin  ;  after  Berres 

10.  Capillary  vessels  of  Intestinal  villi ;  after  Berres  . 

11.  Capillary  vessels  around  orifices  of  Mucous  follicles  ;  after  Berres 

12.  Capillary  vessels  around  follicles  of  Parotid  Gland ;  ditto 

13.  Distribution  of  Sensory  nerves  in  Skin  ;  after  Gerber 

14.  Primary  membrane,  with  germinal  spots ;  after  Goodsir  . 

15.  Primary  membrane,  showing  component  cells  ;  after  Goodsir 

16.  Cells  from  Chorda  Dorsalis  of  Lamprey,  after  Quekett 

17.  Multiplication  of  Cartilage-cells  by  duplication;  after  Leidy 

18.  Parent-cells,  with  contained  secondary  cells,  of  cancerous  structure;  after 

Lebert      ......... 

19.  Cells  from  fluid  of  Herpes ;  after  Addison        .... 

20.  Oblique  section  of  Epidermis  ;  after  Henle  .... 

21.  Epidermic  cells  from  Conjunctiva  ;  after  Gerber 

22.  Portion  of  Choroid-coat,  showing  pigment  cells  ;  ditto. 

23.  Separate  Pigment-cells ;  after  Mandl  ..... 

24.  Detached  epithelium-cells  from  mucous  membrane  of  mouth  ;  after  Lebert 

25.  Pavement-epithelium  from  bronchial  tubes :  after  Lebert 

26.  Layer  of  cylindrical  epithelium,  with  cilia  ;  after  Henle    . 

27.  Follicles  from  liver  of  Crab,  with  contained  secreting  cells ;  after  Goodsir 

28.  Follicles  of  Mammary  gland,  with  contained  secreting  cells  ;  after  Lebert 

29.  Secreting  Cells  of  Human  Liver  ..... 

30.  Formation  of  Spermatozoa  within  cells  ;  after  Wagner 

31.  Diagram  of  Intestinal  Mucous  membrane,  in  intervals  of  digestion;    after 

Goodsir  ........ 

32.  Extremity  of  Placental  villus ;  after  Goodsir  .  .  .  , 

33.  Progressive  stages  of  cell-growth,  in  Shell-membrane  (original) 

34.  Progressive  stages  of  coalescence  of  cells,  in  Shell-membrane  (original) 

35.  Fusiform  tissue  of  plastic  exudations ;  after  Lebert 

36.  Areolar  and  Adipose  tissue ;  after  Mandl  .... 

37.  Capillary  network  around  Fat-cells  :  after  Berres 

38.  Cartilage  of  Mouse's-ear;  after  Quekett  .... 

39.  Section  of  Cartilage  ;  after  Schwann  ..... 

40.  Distribution  of  vessels  on  surface  of  Cartilage ;  after  Toynbee 

41.  Nutrient  vessels  of  Cornea;  after  Toynbee  .... 

42.  Shell  of  Echinus  (original)        ...... 

43.  Sections  of  Shell  of  Pinna  (original)  .... 

44.  Tubular  shell-structure  from  Anomia  (original) 


31 
115 
115 
119 
120 
120 
121 
123 
127 
127 
127 
127 
127 
128 
130 
131 
132 

132 
134 
141 
141 
143 
143 
145 
145 
146 
148 
148 
148 
150 

152 
153 
156 
156 
158 
158 
158 
161 
162 
163 
165 
167 
169 
170 


45.  Cancellated  structure  at  extremity  of  Femur  ;  after  Toynbee       .  .  173 


xu 


LIST   OF  WOOD   ENGRAVINGS. 


46.  Lacunas  of  Osseous  substance  ;  after  Mandl 

47.  Section  of  Bony  Scale  of  Lepidosteus  (original)     . 

48.  Network  of  Haversian  canals,  from  vertical  section  of  Tibia ;  after  Mandl 

49.  Transverse  section  of  long  bone;  after  Wilson 
60.  Section  of  Cartilage,  near  seat  of  Ossification;  after  Wilson 

51,  Section  of  Cartilage,  at  the  seat  of  Ossification ;  after  Wilson 

52.  Vessels  of  Dental  Papilla ;  after  Berres 
63.  Oblique  Section  of  Dentine  ;  after  Owen 

54.  Vertical  Section  of  human  molar  tooth  ;  after  Nasmyth 

55.  Development  of  Teeth  ;  after  Goodsir 
66.  Structure  of  Hair  of  Musk-deer  and  Sable  (original) 

57.  Structure  of  the  Human  Hair;  after  Wilson 

58.  Fasciculus  of  striated  Muscular  fibre  ;  after  Mandl     . 
69.  Non-striated  Muscular  fibres  ;  after  Bowman 

60.  Striated  Muscular  fibre  separating  into  fibrillte 

61.  Muscular  fibre  cleaving  into  disks;  after  Bowman 

62.  Transverse  section  of  muscular  fibres ;  after  Bowman 

63.  Structure  of  ultimate  fibrillse  of  striated  fibre  (original)     . 

64.  Nucleated  fibres  from  non-striated  muscle  ;  after  Wilson 

65.  Fusiform  contractile  cells  ;  after  Kolliker  .        •     . 

66.  Nuclei  in  striated  muscular  fibres  of  foetus  ;  after  Bowman 

67.  Capillaries  of  muscle  ;  after  Berres 

68.  Distribution  of  nerves  in  Muscle ;  after  Burdach 

69.  Components  of  gray  substance  of  brain  ;  after  Purkinje   . 

70.  Capillaries  of  Nervous  centres ;  after  Berres   . 

71.  Structure  of  Ganglion  of  Sympathetic;  after  Valentin 

72.  Distribution  of  Sensory  nerves  in  lip  ;^after  Gerber      . 

73.  Capillaries  at  margin  of  lips  ;  after  Berres 

74.  Section  of  Human  Stomach       ..... 

75.  Mucous  coat  of  small  intestine,  showing  Villi,  and  orifices  of  follicles ;  after 

Boehm      ........ 

76.  Peyerian  glandula ;  after  Boehm  .... 

77.  Stomach  of  Sheep    ....... 

78.  Section  of  Stomach  of  Sheep,  showing  derai-canal ;  after  Flourens 

79.  Lobule  of  Parotid  Gland ;  after  Wagner     .... 

80.  Gastric  glandulse  after  Wagner  .... 

81.  Orifices  of  Gastric  tubuli ;  after  Boyd         .... 

82.  Distribution  of  Capillaries  in  Intestinal  Villus ;  after  Berres 

83.  Commencement  of  Lacteal  in  Intestinal  Villus ;  after  Krause 

84.  Diagram  of  Lymphatic  gland ;  after  Goodsir     . 

85.  Epithelial  cells  of  intra-glandular  Lymphatic ;  after  Goodsir 

86.  Course  of  Thoracic  duct  ..... 

87.  Appearance  of  inflamed  Blood;  after  Addison 

88.  Vascular  area  of  Fowl's  egg  ;  after  Wagner     . 

89.  Diagram  of  the  Circulation  in  Fish 

90.  Diagram  of  the  Circulation  in  Reptile  . 

91.  Diagram  of  complete  Double  Circulation. 

92.  Anatomy  of  Human  Heart  and  Lungs 

93.  Capillaries  of  Nervous  centres,  after  Berres 

94.  Capillaries  of  Glandular  follicles ;  after  Berres 

95.  Capillaries  of  Conjunctival  membrane:  after  Berres 

96.  Capillaries  of  Choroid  coat ;  after  Berres 

97.  Capillaries  around  orifices  of  mucous  follicles;  after  Berres 

98.  Capillaries  in  Skin  of  finger ;  after  Berres 

99.  Capillaries  in  fungiform  papilla  of  Tongue ;  after  Berres. 

100.  Doris,  showing  branchial  tufts  ;  after  Alder  and  Hancock 

101.  One  of  the  arborescent  processes  of  gills  of  Poris;  ditto 

102.  Respiratory  apparatus  of  Insects  .... 

103.  Diagram  of  diflFerent  forms  of  Respiratory  Apparatus  (original) 

104.  Capillaries  of  Gill  of  Eel  (original)        .... 

105.  Section  of  Lung  of  Turtle;  after  Boj anus 

106.  Capillaries  of  Human  Lung  (original) 

107.  Simple  glandular  follicles  ;  after  Miiller     . 

108.  Embryonic  development  of  Liver  ;  after  MUller 


LIST   OF  WOOD   ENGRAVINGS. 


xm 


FIG. 

109. 
110. 
111. 
112. 
113. 
114. 
115. 
116. 
117. 
118. 
119. 
120. 
121. 
122. 
123. 
124. 
125. 
126. 
127. 
128. 
129. 
130. 
131. 
132. 
133. 
134. 

135. 

136. 
137. 
138. 
139. 
140. 
141. 
142. 
143. 

144. 
145. 

146. 

147. 
148. 
149. 
150. 
151. 
152. 
153. 
154. 

155. 

156. 

157. 
158. 
159. 
160. 
161. 
162. 
163. 
164. 
165. 


PA0E. 


Rudimentary  Pancreas,  from  Cod ;  after  Miiller 
Mammary  Gland  of  Ornithorhyncus  ;  after  Miiller     . 
Meibomian  Glands ;  after  Miiller  ..... 

Portion  of  Cowper's  Gland  ;  after  Miiller 

Lobule  of  Lachrymal  Gland  ;  after  Miiller 

Hepatic  Follicles  from  Crab  ;  after  Goodsir    . 

Ultimate  follicles  from  Mammary  gland  ;  after  Lebert     . 

Surface  of  Lobule  of  Liver  of  Squilla ;  after  Miiller 

Interior  of  Lobule  of  Liver  of  Squilla ;  after  Miiller 

Liver  of  Tadpole ;  after  Miiller  .  .  •  • 

Distribution  of  Blood-vessels  in  Lobules  of  Liver  ;  after  Kiernan 

Connexion  of  Lobules  of  Liver  with  Hepatic  vein  ;  ditto 

Distribution  of  Hepatic  ducts,  around  Lobules  of  Liver  ;  after  Kiernan 

Secreting  Cells  of  Liver      ...... 

Development  of  Kidney,  in  embryo  of  Lizard ;  after  Miiller  . 
Kidney  of  foetal  Boa ;  after  Miiller  .  .  .  .• 

Portion  of  Kidney  of  Coluber ;  after  Miiller   .... 

Fasciculus  of  tubuli  uriuiferi  of  Bird ;  after  Miiller 

Section  of  Kidney         ....... 

Section  of  portions  of  Kidney,  slightly  magnified  ;  after  Wagner 

Distribution  of  vessels  in  Kidney ;  after  Bowman 

Vertical  section  of  Skin ;  after  Wilson       .... 

Hepatic  Cells  gorged  with  Fat ;  after  Bowman 

Various  stages  of  development  of  Haematococcus  binalis ;  after  Hassal 
Successive  stages  of  development  of  simpler  Algae  ;  after  Kiitzing    . 
Diagram  representing  the  three  principal  forms  of  the  Generative  process  in 

Plants  (original)         ....... 

Successive  stages  of  Segmentation  of  the  vitellus  of  Ascaris  ;  after  Bagge 
Anatomy  of  the  Testis  .  .  .  .  .  . 

The  Uterus  and  its  appendages     ...... 

Successive  stages  of  segmentation  of  Mammalian  vitellus ;  after  Coste 
Formation  of  the  Mulberry  mass  ;  after  Coste       .... 

Plan  of  Early  Uterine  Ovum  ;  .after  Wagner  .... 

Germ  and  surrounding  parts  ;  after  Coste  .... 

Vascular  Area  of  Fowl's  Egg ;  after  Wagner  .... 

Diagram  of  Ovum,  at  commencement  of  separation  of  digestive  cavity ;  after 

Wagner       ........ 

Diagram  of  Ovum,  showing  the  formation  of  the  Amnion  ;  after  Wagner 
Diagram  of  Human  Ovum,  in  second  month,  showing  the  Allantois ;  after 

Wagner  ........ 

Diagram  of  the  Circulation  in  the  Ovum  at  the  commencement  of  the  forma 

tion  of  the  placenta ;  after  Coste         ..... 
Extremity  of  Placental  Villus  ;  after  Goodsir 
External  membrane  and  cells  of  placental  villus  ;  after  Goodsir 
Diagram  illustrating  the  arrangement  of  the  placental  decidua ;  after  Goodsir 
Plan  of  the  Foetal  Circulation        .  .  .  .  . 

Termination  of  portion  of  milk-duct  in  follicles ;  after  Sir  A.  Cooper 
Portion  of  the  Ganglionic  tract  of  Polydesmus  ;  after  Newport 
Human  embryo  at  sixth  week ;  after  Wagner 


Dissection  of  the  Medulla  Oblongata,  showing  the  connexions  of  its 
tracts  ;  after  Solly  (altered)  .... 

Diagram  of  the  relations  of  the  Cerebrum  to  the  Sensory  Ganglia,  as 
horizontal  section  (original)  .... 

Diagram  of  the  relations  of  the  several  parts  of  the  Encephalon,  as 
vertical  section  (original)  .... 

Capillary  network  at  margin  of  Lips  ;  after  Berres 

Distribution  of  tactile  nerves  in  Skin ;  after  Gerber  . 

Capillaries  of  fungiform  papilla  of  Tongue  ;  after  Berres 

Distribution  of  Olfactory  nerve  ;  after  Wilson 

Diagram  of  the  Auditory  apparatus;  after  Wilson 

Refraction  of  rays  of  light  through  convex  lens 

Formation  of  images  in  eye  .... 

Capillary  network  of  Retina ;  after  Berres 

Structure  of  the  Larynx ;  after  Willis 


several 


EXPLANATION  OF  PLATE  L 


The  Figures  in  this  Plate  represent  the  Cells  floating  in  the  various  animal  fluids  ;  and 
they  are  all,  with  the  exception  of  Figs.  4  and  5,  copied  from  the  representations  given 
by  M.  Donn^  in  his  "Atlas  de  I'Anatomie  Microscopique."  These  representations  are 
transcripts  of  Daguerreotype  pictures,  obtained  from  the  objects,  by  a  solar  microscope, 
with  a  magnifying  power  of  400  diameters. 

Fig.  1.  Red  Corpuscles  of  Human  Blood,  viewed  by  their  flattened  surfaces  (§  215). 

Fig.  2.  Red  Corpuscles  of  Human  Blood,  adherent  by  their  flattened  surfaces,  so  as  to 
form  rolls  ; — at  a,  the  entire  surfaces  are  adherent ;  at  6,  their  surfaces  adhere 
only  in  part. 

Fig.  3.  Red  Corpuscles  of  Human  Blood,  exhibiting  the  granulated  appearance  which 
they  frequently  present,  a  short  time  after  being  withdrawn  from  the  vessels. 

Fig.  4.  Colourless  Corpuscles  of  Human  Blood  (|  214). 

Fig.  6.  The  same,  enlarged  by  imbibition  of  water. 

Fig.  6.  Red  Corpuscles  of  Frog's  Blood  (§  215). 

Fig.  7.  The  same,  treated  with  dilute  acetic  acid ;  the  first  effect  of  which  is  to  render 
the  nucleus  more  distinct,  as  at  5 ;  after  which  the  outer  vesicle  becomes 
more  transparent,  and  its  solution  commences,  as  at  a. 

Fig.  8.  The  same,  treated  with  water ;  at  a  is  seen  a  corpuscle  nearly  unaltered,  except 
in  having  the  nucleus  more  sharply  defined ;  at  b,  others  which  have  become 
more  spherical,  under  the  more  prolonged  action  of  water ;  at  c,  the  nucleus 
is  quitting  the  centre,  and  approaching  the  circumference,  of  the  disk  ;  at  d 
it  is  almost  freeing  itself  from  the  envelope ;  and  at  e  it  has  completely 


Fig.    9.  Globules  of  Mucus,  newly  secreted  (§  237). 

Fig.  10.  The  same,  acted  on  by  acetic  acid. 

Fig.  11.  Globules  of  Pus,  from  a  phlegmonous  abscess  (^  637). 

Fig.  12.  The  same,  acted  on  by  acetic  acid. 


FLATE  1 


(i> 


m 


9 


fc^ 


-v^#«' 


PLATE  21 


14 


SinrJairs  iith.  /^'2- 


EXPLANATION  OF  PLATE  IL 


The  Figures  in  this  Plate  represent  the  principal  forms  of  the  Nervous  Centres  in  diffe- 
rent classes  of  animals.  The  1st  is  copied  from  a  Memoir  by  M.  Blanchard  ;  the  2d, 
3d,  and  4th,  from  Mr.  Newport's  delineations  ;  the  5th  to  the  13th  from  the  work  of  M. 
Guillot  on  the  Comparative  Anatomy  of  the  Encephalon  in  the  different  classes  of  Verte- 
brata  ;  and  the  last  two  from  the  work  of  M.  Leuret  on  the  same  subject. 

Fig.  1.  Nervous  System  of  Solen;  a,  a,  cephalic  ganglia,  connected  together  by  a  trans- 
verse band  passing  over  the  (Esophagus,  and  connected  with  the  other  ganglia 
by  cords  of  communication ;  b,  pedal  ganglion,  the  branches  of  which  are 
distributed  to  the  powerful  muscular  foot ;  c,  branchial  ganglion,  the  branches 
of  which  proceed  to  the  gills  d,  d,  the  siphons  e,  e,  and  other  parts.  On  some 
of  these  branches,  minute  ganglia  are  seen  ;  as  also  at/,  /,  on  the  trunks  that 
pass  forwards  from  the  cephalic  ganglia  (^  852). 

Fig.  2.  Nervous  System  of  the  Larva  of  Sphinx  ligustri;  a,  cephalic  ganglia ;  1-12, 
ganglia  of  the  ventral  cord  (§  856). 

Fig.  3.  Thoracic  portion  of  the  Nervous  System  of  the  Pupa  of  Sphinx  ligustri;  a,  6,  c, 
three  ganglia  of  the  ventral  cord ;  d^  d,  their  connecting  trunks  ;  e,  e,  respira- 
tory ganglia  (^  862). 

Fig.  4.  Anterior  portion  of  the  Nervous  System  of  the  Imago  of  Sphinx  ligustri;  a,  cepha- 
lic ganglia;  b,  b,  eyes  ;  c,  anterior  median  ganglion,  and  d,  d,  posterior  lateral 
ganglia  of  stomato-gastric  system  ;  g,  /,  large  ganglionic  masses  in  the  thorax, 
giving  origin  to  the  nerves  of  the  legs  and  wings  (§  863). 

Fig.  5.  Brain  of  the  Perch,  seen  from  above  (g  869). 

Fig.  6.  The  same,  as  seen  from  below. 

Fig.  7.  Interior  of  the,  same,  as  displayed  by  a  vertical  section. 

The  following  references  are  common  to  the  three  preceding,  and  to  the  succeeding 
figures. 

a,  «,  Olfactory  lobes  or  ganglia. 

b,  b,  Cerebral  ganglia  or  Hemispheres. 

c,  c,  Optic  lobes. 

d,  Cerebellum. 

e,  Spinal  Cord. 
/,  Pineal  gland. 

g,  Lobi  inferiores  (their  precise  character  not  determined). 
h,  Pituitary  body. 
i,  Optic  Nerves. 


XVI  EXPLANATION   OF   PLATE   II. 

Fig.  8.  Brain  of  the  Common  Lizard,  seen  from  above  (§  871). 

Fig.  9.  The  same,  as  seen  from  below. 

Fig.  10.  The  same,  as  displayed  by  a  vertical  section. 

Fig.  11.  Brain  of  the  Common  Goose,  as  seen  from  above  (§  872). 

Fig.  12.  The  same,  as  seen  from  below. 

Fig.  13.  The  same,  as  displayed  by  a  vertical  section. 

Fig.  14.  Brain  of  the  Sheep,  viewed  sideways  (|  873). 

Fig.  15.  The  same,  as  displayed  by  a  vertical  section. 

In  addition  to  the  parts  indicated  by  the  preceding  references,  we  have  here  to 
notice ; — k,  the  corpus  callosum  ;  I,  the  septum  lucidum  ;  and  m,  the  Pons  Varolii. 


BOOK  I. 

GENEKAL    PHYSIOLOGY. 


CHAPTER  I. 

ON  THE  NATURE  AND  OBJECTS  OF  THE  SCIENCE  OF  PHYSIOLOGY. 

1.  The  general  distribution  of  the  objects  presented  to  us  by  external 
nature,  into  three  kingdoms — the  Animal,  the  Vegetable,  and  the  Mine- 
ral,— is  familiar  to  every  one ;  and  not  less  familiar  is  the  general  distinc- 
tion between  living  bodies,  and  dead  inert  matter.    True  it  is,  that  we  can- 
not always  clearly  assign  the  limits  which  separate  these  distinct  classes 
of  objects.     Even  the  professed  Naturalist  is  constantly  subject  to  per- 
plexity as  to  the  exact  boundary  between  the  Animal  and  the  Vegetable 
kingdoms ;  and  the  distinction  between  Animal  and  Vegetable  struc- 
tures, on  the  one  hand,  and  Mineral  masses  on  the  other, — or  between 
living  bodies,  and  aggregations  of  inert  matter, — is  by  no  means  so 
obvious  in  every  case,  as  to  be  at  once  perceptible  to  the  unscientific 
observer.     Thus,  a  mass  of  Coral,  if  its  growing  portion  be  kept  out  of 
view,  or  a  solid  Nullipore  attached  to  the  surface  of  a  rock,  might  be 
easily  confounded  with  the  mineral  bodies  to  which  they  bear  so  close  a 
resemblance ;  and  a  minute  examination  might  be  required  to  detect  the 
difference.     Nevertheless,  a  well-marked  distinction  does  exist,  between 
the  organized  structures  of  Plants  and  Animals,  and  the  inorganic 
aggregations  of  Mineral  matter ;  as  well  as  between  the  condition  of 
a  living  being,  whether  Animal  or  Plant,  and  that  of  dead  or  inert 
Mineral  bodies.     It  is  upon  these  distinctions,  which  are  usually  obvious 
enough,  that  the  sciences  of  Anatomy  and  Physiology  are  founded;: 
these  sciences  taking  cognizance, — the  former,  of  those  structures  which 
are  termed  organized^ — and  the  latter,  of  the  actions  which  are  peculiar 
to  those  structures,  and  which  are  distinguished  by  the  term  vital.     It 
will  be  desirable  to  consider,  in  a  somewhat  systematic  order,  the  prin- 
cipal ideas  which  we  attach  to  these  terms ;  as  we  shall  be  thus  led  most 
directly  to  the  distinct  comprehension  of  the  nature  and  objects  of  Phy- 
siological science. 

2 


18  NATURE   AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 


1.    General  Characters  of  Organized  Structures. 

2.  Organized  structures  are  characterized,  in  the  first  place,  by  the 
peculiarities  of  their  form. — Wherever  a  definite  form  is  exhibited  by 
Mineral  substances,  it  is  bounded  by  straight  lines  and  angles,  and  is 
the  effect  of  the  process  termed  crystallization.  This  process  results 
from  the  tendency  which  evidently  exists  in  particles  of  matter,  espe- 
cially when  passing  gradually  from  the  fluid  to  the  solid  state,  to  arrange 
themselves  in  a  regular  and  conformable  manner  in  regard  to  one  ano- 
ther. There  is,  perhaps,  no  inorganic  element  or  combination,  which  is 
not  capable  of  assuming  such  a  form,  if  placed  in  circumstances  adapted 
to  the  manifestation  of  this  tendency  among  its  particles ;  but  if  these 
conditions  should  be  wanting,  and  the  simple  cohesive  attraction  is  ex- 
ercised in  bringing  them  together,  without  any  general  control  over 
their  direction,  an  indefinite  or  shapeless  figure  is  the  result. — Neither 
of  these  conditions  finds  a  parallel  in  the  Organized  creation.  From 
the  highest  to  the  lowest,  we  find  the  shape  presenting  a  determinate 
character  for  each  species  or  race,  with  a  certain  limited  amount  of 
variation  amongst  individuals  ;  and  this  shape  is  such,  that,  instead  of 
being  circumscribed  within  plane  surfaces,  straight  lines,  and  angles, 
organized  bodies  are  bounded  by  convex  surfaces,  and  present  rounded 
outlines.  We  may  usually  gather,  moreover,  from  their  external  form, 
that  they  are  composed  of  a  number  of  dissimilar  parts,  or  organs; 
which  are  combined  together  in  the  one  individual  body,  and  are  cha- 
racteristic of  it.  Thus  in  the  Vertebrated  or  Articulated  animal,  we  at 
once  distinguish  the  head  and  extremities  from  the  trunk,  which  consti- 
tutes the  principal  mass ;  and  where  there  exist  no  external  organs  of 
such  distinctness,  as  in  some  Molluscs,  the  rounded  character  of  the 
general  form  is  sufficiently  characteristic.  The  very  simplest  grades  of 
animal  and  vegetable  life  present  themselves  under  a  shape,  which  ap- 
proaches more  or  less  closely  to  the  globular.  It  is  among  the  lower 
tribes  of  both  kingdoms,  that  we  find  the  greatest  tendency  to  irregular 
departures  from  the  typical  form  of  the  species ;  and  thus  is  presented 
an  approach,  on  the  one  hand,  to  that  inclefiniteness  which  is  characte- 
ristic of  uncrystalline  mineral  masses ;  and,  on  the  other,  to  that  variety 
of  crystalline  forms  which  the  same  mineral  body  may  present,  accord- 
ing to  the  circumstances  which  influence  its  crystallization. 

3.  With  regard  to  size,  again,  nearly  the  same  remarks  apply.  The 
magnitude  of  Inorganic  masses  is  entirely  indeterminate,  being  altoge- 
ther dependent  upon  the  number  of  particles  which  can  be  brought 
together  to  constitute  them.  On  the  other  hand,  the  size  of  Organized 
•  structures  is  restrained,  like  their  form,  within  tolerably  definite  limits, 
which  may  nevertheless  vary  to  a  certain  extent  among  the  individuals 
of  the  same  species.  These  limits  are  least  obvious  in  vegetables,  and 
in  the  lower  classes  of  animals.  A  forest-tree  may  go  on  extending 
itself  to  an  almost  indefinite  extent ;  certain  species  of  sea-weed  attain 
a  length  of  many  hundred  feet,  and  their  growth  does  not  appear  to  be 
restrained  by  any  limit ;  and  the  same  may  be  said  of  those  enormous 
masses  of  coral,  which  compose  so  many  islands  and  reefs  in  the  Poly- 


OF  ORGANIZED  STRUCTURES  IN  GENERAL.  19 

nesian  Archipelago,  or  of  which  the  debris  seem  to  have  constituted 
many  of  the  calcareous  rocks  of  ancient  formation.  But  in  these  cases, 
the  increase  is  produced  by  the  multiplication  of  similar  parts,  which, 
when  once  completely  evolved,  have  but  little  dependence  upon  one  ano- 
ther, and  might  be  almost  considered  as  distinct  individuals.  Thus, 
each  bud  of  a  tree,  if  placed  under  favourable  circumstances,  can  main- 
tain its  life  by  itself,  and  can  perform  all  the  actions  proper  to~  the 
species.  Each  polype  of  the  coral  mass,  in  like  manner,  at  first  pro- 
duced by  a  process  of  budding  from  the  original  stock,  comes  in  time  to 
be  completely  independent  of  it,  and  of  those  with  which  it  is  associated. 
And  in  the  sea-weed,  each  portion  of  the  frond  is  an  almost  precise  repe- 
tition of  every  other,  and  grows  for  and  by  itself ;  neither  receiving 
from  nor  communicating  to,  any  other  part,  the  materials  of  its  organic 
structure.  Thus  among  Plants  and  the  lower  Animals,  we  find  an 
indefiniteness  in  point  of  size,  depending  upon  the  tendency  to  multiplica- 
tion of  similar  parts,  which  has  been  designated  as  vegetative  repetition. 

4.  It  is,  however,  in  the  internal  arrangement  or  aggregation  of  the 
particles,  respectively  composing  Organized  structures  and  Inorganic 
masses,  that  we  find  the  difference  between  the  two  most  strongly 
marked. — Every  particle  of  a  Mineral  body  (in  which  there  has  not 
been  a  mixture  of  ingredients)  exhibits  the  same  properties  as  those 
possessed  by  the  whole ;  so  that  the  chemist,  in  experimenting  with  any 
substance,  cares  not,  except  as  a  matter  of  convenience  merely,  whether 
a  grain  or  a  ton  be  the  subject  of  his  researches.  The  minutest  atom  of 
carbonate  of  lime,  for  instance,  has  all  the  properties  of  a  crystal  of  this 
substance,  were  it  as  large  as  a  mountain.  Hence  we  are  to  regard  a 
mineral  body  as  made  up  of  an  indefinite  number  of  constituent  particles, 
similar  to  it  and  to  each  other  in  properties,  and  having  no  further  re- 
lation among  themselves  than  that  which  they  derive  from  their  juxta- 
position. Each  particle,  then,  may  be  considered  as  possessing  a  sepa- 
rate individuality ;  since  we  can  predicate  of  its  properties  all  that  can 
be  said  of  the  largest  mass. — The  Organized  structure,  on  the  other 
hand,  receives  its  designation  from  being  made  up  of  a  number  of  dis- 
tinct parts  or  organs,  each  of  which  has  a  texture  or  consistence  peculiar 
to  itself;  and  it  derives  its  character  from  the  whole  of  these  collectively. 
Every  one  of  these,  as  we  shall  hereafter  see,  is  the  instrument  of  a 
certain  action  or  function,  which  it  performs  under  certain  conditions ; 
and  the  concurrence  of  all  these  actions  is  required  for  the  maintenance 
of  the  structure  in  its  normal  or  regular  state,  and  for  the  prevention 
or  the  reparation  of  those  changes,  which  chemical  and  physical  forces 
would  otherwise  speedily  produce  in  it,  from  causes  hereafter  to  be  ex- 
plained. Hence  ther.e  is  a  relation  of  mutual  dependence  among  the 
parts  of  an  Organized  structure ;  which  is  quite  distinct  from  that  of 
mere  proximity.  Thus,  the  perfect  plant,  which  has  roots,  stem,  leaves, 
and  flowers,  is  an  example  of  an  organized  structure,  in  which  the  rela- 
tion of  the  different  parts  to  the  integrity  of  the  whole  is  sufficiently 
obvious ;  since,  when  entirely  deprived  of  either  set  of  these  organs,  the 
race^  must  perish,  unless  the  plant  have  within  itself  the  power  of  re- 
placing them. 

5.  It  is  not  only  in  Zoophytes  and  other  aggregate  Animals,  that  we 


20  NATURE  AND   OBJECTS   OF   PHYSIOLOGHCAL   SCIENCE. 

notice  the  tendency  to  "vegetative  repetition;"  for  it  may  be  observed 
in  many  animals  which  can  be  divided  without  the  destruction  of  their 
lives, — especially  among  the  Radiated,  and  the  lower  Articulated  tribes. 
Where  such  a  repetition  exists,  some  of  the  organs  may  be  removed  with- 
out permanent  injury  to  the  structure ;  their  function  being  performed 
by  those  that  remain.  Thus  it  is  not  uncommon  to  meet  with  specimens 
of  the  common  five-rayed  Starfish,  in  which  not  only  one  or  two,  but  even 
three  or  four,  of  the  arms  have  been  lost  without  the  destruction  of  the 
animal's  life;  and  this  is  the  more  remarkable,  as  the  arms  are  not 
simply  organs  of  locomotion  or  prehension,  but  contain  prolongations  of 
the  stomach.  In  the  bodies  of  the  higher  animals,  however,  where  there 
are  few  or  no  such  repetitions  (save  on  the  two  sides  of  the  body),  and 
where  there  is  consequently  a  greater  diversity  in  character  and  function 
between  the  different  organs,  the  mutual  dependence  of  their  actions  upon 
one  another  is  much  greater,  and  the  loss  of  a  single  part  is  much  more 
likely  to  endanger  the  existence  of  the  whole.  Such  structures  are  said 
to  be  more  highly  organized  than  those  of  the  lower  classes ;  not  because 
the  whole  number  of  parts  is  greater, — for  it  is  frequently  much  less ; 
but  because  the  number  of  dissimilar  parts,  and  the  consequent  adap- 
tation to  a  variety  of  purposes,  is  much  greater, — the  principle  of  divi- 
sion of  labour,  in  fact,  being  carried  much  further,  a  much  larger  class 
of  objects  being  attained,  and  a  much  greater  perfection  in  the  accom- 
plishment of  them  being  thus  provided  for. 

6.  Keeping  in  view,  then,  what  has  just  been  stated  in  regard  to  the 
divisibility  of  a  Tree  or  a  Zoophyte  into  a  number  of  parts,  each  capable 
of  maintaining  its  own  existence,  we  may  trace  a  certain  gradation  from 
the  condition  of  the  Mineral  body  to  that  of  the  highest  Animal,  in 
regard  to  the  character  in  question.  Thus,  the  individuality  of  a  Mi- 
neral substance  may  be  said  to  reside  in  each  molecule  ;  that  of  a  Plant 
or  Zoophyte,  in  each  complete  member ;  and  that  of  one  of  the  higher 
Animals,  in  the  sum  of  all  the  organs.  The  distinction  is  much  greater, 
however,  between  the  lowest  organized  fabric  and  any  mineral  body, 
than  it  is  between  the  highest  and  the  lowest  organized  structures ;  for,  as 
we  shall  hereafter  see,  the  highest  and  most  complicated  may  be  regarded 
as  made  up  of  an  assemblage  of  the  lowest  and  simplest ;  whose  structure 
and  actions  have  been  so  modified  as  to  render  them  mutually  depen- 
dent; but  which  yet  retain  a  separate  individuality,  such  as  enables 
them  to  continue  performing  their  functions  when  separated  from  the 
mass,  so  long  as  the  proper  conditions  are  supplied. 

7.  Between  the  very  simplest  Organized  fabric,  and  every  form  of 
Mineral  matter,  there  is  a  marked  difference  in  regard  to  intimate  struc- 
ture and  consistence.  Inorganic  substances  can  scarcely  be  regarded  as 
possessing  a  structure ;  since  (if  there  be  no  admixture  of  components) 
they  are  uniform  and  homogeneous  throughout,  whether  existing  in  the 
solid,  the  liquid,  or  the  gaseous  form ;  being  composed  of  similar  parti- 
cles, held  together  by  attractions  which  affect  all  alike.  Far  different 
is  the  character  of  Organized  structures ;  for  in  the  minutest  parts  of 
these  may  be  detected  a  heterogeneous  composition, — a  mixture  of  solid 
and  fluid  elements,  which  are  so  intimately  combined  and  arranged,  as 
to  impart  such  peculiarities  to  the  tissues,  even  in  regard  to  their  physi- 


OF  ORGANIZED  STRUCTURES  IN  GENERAL.  21 

cal  properties,  as  we  never  encounter  amongst  Mineral  bodies.  In  the 
latter,  solidity  or  hardness  may  be  looked  upon  as  the  characteristic  con- 
dition ;  whilst  in  Organized  structures,  softness  (resulting  from  the  large 
proportion  of  fluid  components)  may  be  considered  the  distinctive  quality, 
being  most  obvious  in  the  parts  that  are  most  actively  concerned  in  vital 
operations.  This  softness  is  evidently  connected  with  the  roundness  of 
form  characteristic  of  Organized  fabrics,  which  is  most  evident  when 
the  tissues  contain  the  greatest  proportion  of  fluid ;  whilst  the  plane 
surfaces  and  angular  contours  of  Mineral  bodies  are  evidently  due  to 
the  mode  in  which  the  solid  particles  are  aggregated  together,  without 
any  intervening  spaces. 

8.  The  greatest  solidity  exhibited  by  Organized  fabrics,  is  found  where 
it  is  desired  to  impart  to  them  the  simple  physical  property  of  resistance ; 
and  this  is  attained  by  the  deposition  of  solid  particles,  often  of  a  mineral 
character,  in  tissues  that  were  originally  soft  and  yielding.  It  is  in  this 
manner  that  the  almost  jelly-like  substance,  in  which  all  the  organs  of 
animals  originate,  becomes  condensed  into  cartilage,  and  that  the  carti- 
lage is  afterwards  converted  into  bone ;  it  is  in  the  same  manner,  also, 
that  the  stones  of  fruit,  and  the  heart-wood  of  timber-trees,  are  formed 
out  of  softer  tissues.  But,  as  we  shall  hereafter  see,  this  kind  of  con- 
version, whilst  it  renders  the  tissue  more  solid  and  durable,  cuts  it  off 
from  any  active  participation  in  the  vital  operations ;  and  thence  reduces 
it  to  a  state  much  more  nearly  analogous  to  that  of  mineral  bodies. 
This  resemblance  is  rendered  more  close  by  the  fact,  that  the  earthy 
deposits  frequently  retain  a  distinctly  crystalline  condition;  so  that, 
when  they  are  present  in  large  proportion,  they  impart  a  more  or  less 
crystalline  aspect  to  the  mass,  and  especially  a  crystalline  mode  of  frac- 
ture, which  is  evident  enough  in  many  shells.  It  must  not  be  hence 
concluded,  however,  that  such  substances  are  of  an  inorganic  nature ; 
all  that  is  shown  by  their  crystalline  structure  being,  that  the  animal 
basis  exists  in  comparatively  small  amount,  and  that  the  mode  in  which 
the  mineral  matter  was  deposited  has  not  interfered  with  its  crystalline 
aggregation. 

9.  It  is  not  to  be  disputed  that  a  certain  degree  of  homogeneity  is 
apparently  to  be  found  in  the  minutest  elements,  into  which  certain 
Organized  tissues  are  to  be  resolved.  Thus,  in  the  membranes  which 
form  the  walls  of  Animal  and  Vegetable  cells,  the  highest  powers  of  the 
microscope  fail  in  detecting  any  such  distinction  of  fluid  and  solid  com- 
ponents, as  that  which  has  been  described  as  characteristic  of  organized 
structures.  Nevertheless  it  is  indubitable  that  such  distinct  components 
must  exist;  and  this  especially  from  the  properties  of  these  membranes 
in  regard  to  water.  For  it  is  one  of  the  most  remarkable  facts  in  the 
whole  range  of  science,  that  a  membrane,  in  which  not  the  •  slightest 
appearance  of  a  pore  can  be  discovered  under  the  highest  powers  of  the 
microscope,  should  be  capable  of  allowing  water  to  pass  through  it ;  and 
that,  too,  with  no  inconsiderable  rapidity.  The  change  which  these 
membranes  undergo  in  drying,  is  another  proof  that  they  are  not  so 
homogeneous  as  they  appear,  and  that  water  is  an  element  of  their  struc- 
ture, not  merely  chemically,  but  mechanically.  The  same  may  be  said 
in  regard  to  the  fibres^  which  form  the  apparently  ultimate  elements  of 


22  NATURE   AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

the  simple  fibrous  tissues  in  Animals,  and  which  are  also  met  with  in  the 
interior  of  certain  cells  and  vessels  in  Plants.  These  fibres  would  appear 
to  be  of  perfectly  simple  structure ;  yet  we  know  from  the  loss  of  fluid, 
and  the  change  of  properties  which  they  undergo  in  drying,  that  water 
must  have  formed  part  of  their  substance. — It  may  be  remarked,  how- 
ever, in  regard  to  both  these  elementary  forms  of  Organized  tissue,  that 
the  simplicity  of  their  function  is  in  complete  conformity  with  the  appa- 
rent homogeneousness  of  their  structure ;  for  the  cell-membrane  is  chiefly 
destined  to  act,  like  the  porous  septum  in  certain  forms  of  the  voltaic 
battery,  as  a  boundary-wall  to  the  contained  fluid,  without  altogether 
interfering  with  its  passage  elsewhere ;  the  forces  which  produce  its 
imbibition  or  expulsion  being  probably  situated,  not  in  this  pervious  wall, 
but  in  the  cavity  which  it  bounds.  And,  in  the  same  manner,  the  func- 
tion of  the  fibrous  tissues,  to  w^hich  allusion  was  just  now  made,  is  of  dn 
entirely  physical  character ;  being  simply  to  resist  strain  or  pressure, 
and  yet  to  allow  of  a  certain  degree  of  yielding  by  their  elasticity. 

10.  In  all  cases  in  which  active  vital  operations  are  going  on,  we  can 
make  a  very  obvious  distinction  of  the  structures  subservient  to  them, 
into  liquid  and  solid  parts ;  and  it  is,  indeed,  by  the  continual  reaction 
which  is  taking  place  between  these,  that  the  fabric  is  maintained  in  its 
normal  condition.  For,  as  we  shall  hereafter  see,  it  is  liable  to  a  constant 
decomposition  or  separation  into  its  ultimate  elements  :  and  it  is  conse- 
quently necessary  that  the  matters  which  have  undergone  that  disinte- 
gration should  be  carried  ofi",  and  that  they  should  be  replaced  by  new 
particles.  These  processes  of  removal  and  replacement,  with  the  various 
actions  subservient  to  them,  make  up  a  large  proportion  of  the  life  of 
all  Organized  beings.  Now  as  all  the  alimentary  matter  must  be  reduced 
to  the  liquid  form,  in  order  that  it  may  be  conveyed  to  the  situations  in 
which  it  is  required,  and  as  all  the  decomposed  or  disintegrated  matter 
must  be  reduced  to  the  same  form  in  order  to  be  carried  ofi",  the  inter- 
mingling or  mutual  penetration  of  solids  and  liquids  in  the  minutest  parts 
of  the  body  is  at  once  accounted  for.  We  shall  hereafter  see  that  a  cell^ 
or  closed  vesicle,  formed  of  a  membranous  wall,  and  containing  fluid, 
may  be  regarded  as  the  simplest  form  of  a  living  body,  and  the  simplest 
independent  part  or  instrument  of  the  more  complex  fabrics  (§  30). 

11.  Organized  structures  are  further  distinguished  from  Inorganic 
masses,  by  the  peculiarity  of  their  cJieinieal  constitution.  This  pecu- 
liarity does  not  consist,  however,  in  the  presence  of  any  elementary  sub- 
stances which  are  not  found  elsewhere ;  for  all  the  elements,  of  which 
organized  bodies  are  composed,  exist  abundantly  in  the  world  around. 
It  might  have  been  supposed  that  beings  endowed  with  such  remarkable 
powers  as  those  of  Animals  and  Plants, — powers  which  depend,  as  we 
shall  hereafter  see,  upon  the  exercise  of  properties  to  which  we  find 
nothing  analogous  in  the  Mineral  world, — would  have  had  an  entirely 
diff'erent  material  constitution  ;  but  a  little  reflection  will  show,  that  the 
identity  of  the  ultimate  elements  of  Organized  structures  with  those  of 
the  Inorganic  world,  is  a  necessary  consequence  of  the  mode  in  which 
the  former  are  built  up.  For  that  which  the  parent  communicates,  in 
giving  origin  to  a  new  being,  is  not  so  much  the  structure  itself,  as  the 
power  of  forming  that  structure  from  the  surrounding  elements ;  and  it 


I 


OP  ORGANIZED  STRUCTURES  IN  GENERAL.  23 

is  by  gradually  drawing  to  itself  certain  of  these  elements,  that  the 
germ  becomes  developed  into  the  complete  fabr,ic.  Now,  of  the  sixty- 
two  simple  or  elementary  substances,  which  are  known  to  occur  in  the 
Mineral  world,  only  about  eighteen  or  nineteen  are  found  in  Plants  and 
Animals ;  and  many  of  these  in  extremely  minute  proportion.  Some  of 
these  appear  to  J^e  merely  introduced,  to  answer  certain  chemical  or 
mechanical  purposes ;  and  the  composition  of  the  parts  which  possess 
the  highest  vital  endowments,  is  for  the  most  part  simpler  and  more 
uniform. 

12.  The  actual  tissues  of  Plants,  when  entirely  freed  from  the  sub- 
stances they  may  contain,  have  been  found  to  possess  a  very  uniform 
composition,  and  to  agree  in  their  chemical  properties.  The  substance 
which  forms  the  principal  part  of  the  thickness  of  the  walls  of  the  cells, 
vessels,  &c.,  of  which  the  Vegetable  organism  is  composed,  is  identical 
with  Starch  in  the  proportion  of  its  components ;  but  as  these  are  in  a 
different  state  of  aggregation,  it  is  distinguished  as  Cellulose,  It  con- 
sists of  12  Carbon,  10  Hydrogen,  and  10  Oxygen ;  or,  in  other  words, 
of  Carbon  united  to  the  elements  of  water,  in  the  proportion  of  eight 
of  the  former  to  seven  of  the  latter.  It  may  be  very  easily  converted 
into  gum  or  sugar,  by  chemical  processes,  which  effect  the  removal  or 
the  addition  of  the  elements  of  water.  Now  there  is  no  compound 
known  to  exist  in  the  Inorganic  world,  which  bears  the  remotest  analogy 
to  this ;  and  we  have  no  reason  to  believe  that  it  could  be  produced  in 
any  other  way,  than  by  that  peculiar  combination  of  force  which  exists 
in  the  growing  Plant.  But  although  Cellulose  is  the  predominating 
component  of  the  Vegetable  fabric,  yet  it  is  not  the  most  essential ;  for 
late  researches  have  shown,  that  within  what  has  been  ordinarily  consi- 
dered as  the  cell-wall,  is  a  delicate  membrane,  termed  the  "  primordial 
utricle,"  which  is  really  the  original  cell-wall,  from  the  exterior  of  which 
the  layer  of  cellulose  is  secreted.  And  it  is  a  very  interesting  fact, 
that  the  composition  of  this  membrane  corresponds  with  that  of  the 
proper  cell-walls  of  the  Animal  tissues;  it  being,  in  fact,  a  proteine 
compound  (§  13).  Hence  every  act  of  Vegetable  growth  involves  the 
production  of  this  substance  also,  which  is  still  more  removed  in  its 
composition  from  ordinary  Inorganic  compounds. 

13.  The  composition  of  the  Animal  tissues,  when  freed  from  the 
fluids  they  may  contain,  or  from  the  solid  matters  which  may  have  been 
deposited  within  them,  is  nearly  as  uniform.  We  may  distinguish 
among  them  two  chiei  proximate  principles,  which  appear  under  various 
modifications  in  a  great  variety  of  dissimilar  parts,  and  which  seem 
capable  of  conversion  into  other  principles  by  the  addition  or  subtrac- 
tion of  some  of  their  constituents.  The  first  and  most  important  of 
these,  named  Proteine,^  consists  of  40  Carbon,  31  Hydrogen,  5  Nitro- 
gen, and  12  Oxygen ;  and  although  its  composition  is  so  complex,  it 
appears^  to  act  like  a  simple  body,  in  uniting  with  Oxygen,  Acids,  &c., 
in  definite  proportions,  as  well  as  with  Sulphur  and  Phosphorus ;  with 

*  Although  it  may  be  doubted  whether  Proteine  has  ever  been  actually  obtained  in  a 
separate  state,  yet  the  term  maybe  conveniently  applied  to  that  composite  base,  which 
is  united  with  different  equivalents  of  sulphur  and  phosphorus  in  the  albuminous  com- 
pounds. 


24  NATURE  AND   OBJECTS    OF   PHYSIOLOGICAL   SCIENCE. 

which  last,  indeed,  it  is  always  found  combined,  in  the  Albumen,  Fibrine, 
&c.,  that  are  commonly  regarded  as  the  organic  constituents  of  the 
Animal  tissues. — The  second  of  the  chief  proximate  principles,  termed 
G-elatine,  is  largely  diffused  through  the  Animal  body ;  but  the  tissues 
which  are  composed  of  it  possess  a  simple  fibrous  structure,  and  a  purely 
mechanical  function ;  and  no  vital  action  seems  to  ta^e  place  in  them, 
subsequently  to  their  first  production.  It  consists  of  13  Carbon,  10 
Hydrogen,  2  Nitrogen,  and  5  Oxygen ;  and  it  is  principally  characte- 
rized by  its  solubility  in  hot  water,  and  by  the  insolubility  of  its  com- 
pound with  tannic  acid. 

14.  We  shall  hereafter  dwell  more  in  detail  upon  the  Chemical  Con- 
stitution of  the  Animal  tissues  and  products  (chap,  hi.)  These  sub- 
stances are  only  noticed  here,  in  illustration  of  the  general  statement, 
that  the  "proximate  principles"  of  Animal  and  Vegetable  bodies  (that 
is,  the  simplest  forms  to  which  their  component  structures  can  be 
reduced,  without  altogether  separating  them  into  their  ultimate  ele- 
ments), are  of  extremely  peculiar  constitution  ;  being  made  up  of  three 
or  four  elements,  of  which  the  atoms  do  not  seem  to  be  united  two  by 
two,  or  by  the  method  of  binary  composition,  but  of  which  a  large 
number  are  brought  together  to  form  one  compound  atom,  of  ternary/ 
or  quaternary  composition.  This  compound  atom,  like  Cyanogen,  and 
many  others  derived  from  Organic  products,  acts  like  a  simple  or  ele- 
mentary one  in  its  combinations  with  other  substances. — It  is  worthy 
of  remark,  however,  that,  in  this  respect  as  in  others,  the  Vegetable 
kingdom  is  intermediate  between-  the  Animal  and  the  Mineral.  For 
whilst  Proteine  and  Gelatine  are  remarkable,  not  only  for  containing 
four  elements,  but  for  the  very  large  number  of  atoms  of  these  compo- 
nents which  enter  into  the  single  compound  atom  of  each ;  the  Cellu- 
lose of  Plants  is  much  simpler  in  its  composition,  since  it  includes  only 
three  elements,  and  the  numbers  which  represent  their  proportions  are 
smaller.  And  further,  the  proportions  of  the  components  of  Cellulose 
are  themselves  such  as  suggest  the  idea  of  simplicity  in  their  method  of 
combination, — the  union  of  water  and  carbon  in  the  common  binary 
method ; — an  idea  which  is  confirmed  by  the  mode  of  its  original  pro- 
duction, which  indicates  a  direct  union  of  carbon  with  water ;  as  well  as 
by  the  fact,  that  the  chemical  difference  between  Cellulose  and  nume- 
rous other  substances  found  in  Plants,  may  be  represented  by  the  simple 
addition  or  subtraction  of  a  certain  number  of  atoms  of  water,  and  that 
the  chemist  can  effect  an  actual  conversion  of  the  former  into  certain  of 
the  latter,  by  means  which  are  calculated  to  effect  such  an  addition  or 
subtraction. 

15.  We  shall  hereafter  see  that  Vegetables  are  intermediate  between 
the  Animal  kingdom  and  the  Inorganic  world  in  another  most  important 
particular — the  nature  of  the  chemical  operations  they  effect ;  for  it  is 
their  function  to  combine  the  oxygen,  hydrogen,  carbon,  and  nitrogen, 
of  the  Inorganic  world  into  Organic  Compounds  ;  which  not  only  serve  as 
the  materials  of  their  own  growth,  but  also  as  the  food  of  Animals,  whose 
existence  is  entirely  dependent  upon  them,  since  they  possess  no  such 
combining  power.  It  is  from  the  Water,  Carbonic  Acid,  and  Ammonia, 
supplied  by  the  atmosphere  and  by  the  soil  in  which  they  are  fixed,  that 


OP  VITAL   ACTIONS   IN   GENERAL.  25 

Plants  derive  these  elements.  On  the  other  hand,  the  Animal,  making 
use  of  the  ternary  and  quaternary  compounds  which  have  been  elabo- 
rated by  Plants,  is  continually  restoring  their  elements  to  the  Inorganic 
world,  in  the  very  forms  which  they  originally  possessed;  for,  as  we 
shall  hereafter  see,  the  excretion  of  Water,  Carbonic  acid,  and  Ammo- 
nia is  constantly  taking  place  in  the  Animal  body  during  life,  aa^the 
result  of  those  changes  in  which  its  peculiar  activity  consists.  And 
thus  is  sustained  that  balance  between  Animal  and  Vegetable  nutrition, 
which  is  found  to  be  the  more  wonderful  and  complete,  the  more  care- 
fully it  is  scrutinized. 

2.  Distinctive  Characters  of  Vital  Actions. 

16.  We  are  now  arrived  at  the  second  head  of  our  inquiry, — namely, 
the  nature  of  those  actions^  which  distinguish  living  beings  from  masses 
of  inert  matter,  and  which  are  designated  as  Vitcd^  to  mark  their  dis- 
tinctness from  Physical  and  Chemical  phenomena.  There  can  be  no 
doubt  whatever,  that,  of  the  many  changes  which  take  place  during  the 
life^  or  state  of  vital  activity ^  of  an  Organized  being,  and  which  inter- 
vene between  its  first  development  and  its  final  decay,  a  large  propor- 
tion are  effected  by  the  direct  agency  of  those  forces,  which  operate  in 
the  Inorganic  world ;  and  there  is  no  necessity  whatever  for  the  suppo- 
sition, that  these  forces  have  any  other  operation  in  the  living  body, 
than  they  would  have  out  of  it  under  similar  circumstances.  Thus  the 
propulsion  of  the  blood  by  the  heart  through  the  large  vessels,  is  a  phe- 
nomenon precisely  analogous  to  the  propulsion  of  any  other  liquid 
through  a  system  of  pipes  by  means  of  a  forcing  pump ;  and  if  the  ar- 
rangement of  the  tubes,  the  elasticity  of  their  walls,  the  contractile 
power  of  the  heart,  and  the  physical  properties  of  the  fluid,  could  be 
precisely  imitated,  the  artificial  apparatus  would  give  us  an  exact  repre- 
sentation of  the  actions  of  the  real  one.  The  motor  force  of  the  muscles 
upon  the  bones,  again,  operates  in  a  mode  that  might  be  precisely  repre- 
sented by  an  arrangement  of  cords  and  levers ;  the  peculiarity  here,  as 
in  the  former  case,  being  solely  in  the  mode  in  which  the  force  is  first 
generated.  So,  again,  the  digestive  operations  which  take  place  in  the 
stomach  are  capable  of  being  closely  imitated  in  the  laboratory  of  the 
chemist ;  when  the  same  solvent  fluid  is  employed,  and  the  same  agencies 
of  heat,  motion,  &c.,  are  brought  into  play.  Moreover  we  shall  here- 
after see  reason  to  believe,  that  the  peculiar  form  of  Capillary  Attrac- 
tion, to  which  the  term  "endosmose"  is  applied,  performs  an  important 
part  in  the  changes  which  are  continually  taking  place  in  the  living  body. 

17.  But  after  every  possible  allowance  has  been  made  for  the  opera- 
tion of  Physical  and  Chemical  forces,  in  the  living  Organism,  there  still 
remain  a  large  number  of  phenomena,  which  cannot  be  in  the  least  ex- 
plained by  them,  and  which  we  can  only  investigate  with  success,  when 
we  regard  them  as  resulting  from  the  agency  of  forces  as  distinct  from 
those  of  Physics  and  Chemistry,  as  they  are  from  each  other.  It  is  to 
these  phenomena  that  we  give  the  name  of  Vital;  the  forces  from 
whose  operation  we  assume  them  to  result,  are  termed  vital  forces  ;  and 
the  properties,  which  we  must  attribute  to  the  substances  manifesting 


26  NATURE   AND   OBJECTS   OP   PHYSIOLOGICAL   SCIENCE. 

those  forces,  are  termed  vital  properties.  Thus  we  say  that  the  act  of 
contraction  in  a  muscle  is  a  vital  phenomenon ;  because  its  character 
appears  totally  distinct  from  that  of  a  Physical  or  Chemical  action ; 
and  because  it  is  dependent  upon  other  vital  changes  in  the  muscular 
substance.  The  act  is  the  manifestation  of  a  certain  force,  the  posses- 
sion of  which  is  peculiar  to  the  muscular  structure,  and  which  is  named 
the  Contractile  force.  But  that  force  is  only  exerted  under  certain  con- 
ditions, and  these  may  only  recur  at  long  intervals,  though  the  capacity 
for  exerting  it  be  always  present  in  the  organized  tissue ;  this  capacity 
is  termed  ^property ;  and  thus  we  regard  it  as  the  essential  peculiarity 
of  living  Muscular  tissue,  that  it  possesses  the  vital  property  of  Con- 
tractility. Or,  to  reverse  the  order,  the  muscle  is  said  to  possess  the 
property  of  Contractility ;  the  property,  when  the  appropriate  conditions 
are  supplied,  gives  rise  to  the  Contractile  Force  ;  and  the  force  produces, 
if  its  operation  be  unopposed,  the  act  of  Contraction. 

18.  It  may  be  said  that  the  distinction  here  made  is  a  verbal  one ; 
and  that  a  very  simple  thing  is  thus  made  complex ;  but  it  will  be  pre- 
sently seen  that  it  is  necessary,  in  order  to  enable  us  to  take  correct 
views  of  the  nature  of  Vital  phenomena,  and  to  understand  their  rela- 
tions to  those  of  the  Inorganic  world.  And,  in  fact,  the  distinction 
between  the  property,  the  force,  and  the  action,  become  apparent  upon 
a  little  consideration.  Of  the  property  we  are  altogether  unconscious, 
so  long  as  it  is  not  called  into  exercise ;  we  could  not,  for  example,  de- 
termine by  the  simple  exercise  of  any  of  our  senses,  whether  a  certain 
piece  of  muscle  retained,  or  had  lost,  its  contractility.  When  the  pro- 
perty is  called  into  action  by  its  appropriate  stimulus,  we  may  convince 
ourselves  that  a  force  is  generated,  even  if  no  sensible  action  is  pre- 
sented ;  thus,  if  we  were  to  hold  the  two  extremities  of  a  muscle  so 
firmly,  as  to  prevent  them  from  approximating  in  the  least  degree  when 
its  contractility  was  excited,  we  should  be  conscious  of  a  powerful  force 
tending  to  draw  our  hands  together  ;  and  we  might  measure  the  amount 
of  that  force,  by  mechanical  means  adapted  to  determine  the  weight  it 
would  sustain.  And  lastly,  if  no  obstacle  be  interposed  to  the  act  of 
contraction,  it  then  becomes  obvious  to  our  senses,  by  the  change  in  the 
shape  of  the  muscle,  and  by  the  approximation  of  its  two  extremities,  as 
well  as  of  the  bodies  to  which  they  are  attached. 

19.  The  advantage  of  this  method  of  viewing  the  phenomena  of  Life 
is  best  shown,  by  turning  our  attention  for  a  moment  to  the  mode  of 
investigation  practised  in  Physics  and  Chemistry.  Thus,  when  a  stone 
falls  towards  the  earth,  we  say  that  this  is  an  act  or  phenomenon  of 
Gravitation.  The  force  with  which  the  stone  tends  to  fall  to  the  ground, 
whether  it  actually  falls  or  not,  is  called  the  force  of  Gravitation ;  and 
we  speak  of  the  tendency  which  every  substance  has  to  act  in  this  mode, 
as  the  property  of  Gravitation.  Now  from  observation  of  the  Moon's 
motion,  it  is  shown  that  she  too  is  drawn  towards  the  Earth ;  her  ellip- 
tical path  around  it  being  the  result  of  the  combined  action  of  the  cen- 
trifugal or  tangential,  and  of  the  centripetal  or  gravitative  forces.  And 
it  is  further  established,  that  not  only  does  the  Moon  gravitate  towards 
the  Earth,  but  the  Earth  gravitates  towards  the  Moon ;  so  that,  if  the 
two  bodies  were  entirely  free  from  the  action  of  all  other  forces,  they 


OF  VITAL   ACTIONS   IN  GENERAL.  27 

would  fall  towards  each  other  (the  distance  traversed  by  each  being  in 
proportion  to  the  size  of  the  other),  and  would  meet  in  their  common 
centre  of  Gravity.  Hence  it  is  evident  that  the  attractive  force  is 
similar  in  both  bodies ;  and  our  idea  of  the  property  of  Gravitation  must 
be  extended,  therefore,  from  the  Earth  to  the  Moon.  Again,  we  find 
ample  reason  to  believe  that  the  same  force  acts  between  the  Sun  and  the 
Planets, — between  the  Planets  and  the  Sun, — and  amongst  the  Planets 
themselves ;  and  further,  careful  experiment  shows  that  masses  of  matter 
upon  the  Earth's  surface  are  not  only  attracted  by  it,  and  attract  it  in 
their  turn,  but  that  they  attract  and  are  attracted  by  each  other.  Hence 
we  arrive  at  the  idea  of  the  universality  of  this  property  of  mutual  at- 
traction ;  and  we  perceive  that,  in  spite  of  varieties  in  the  actions  it 
produces,  and  of  difi'erences  in  the  amounts  of  the  forces  to  which  it 
gives  rise,  the  property  is  the  same  throughout ;  so  that  we  can  predict 
all  these  actions,  and  anticipate  the  forces  which  will  be  developed,  from 
the  simple  general  expression  of  the  property  of  Mutual  Attraction,  and 
of  the  conditions  under  which  it  is  manifested, — constituting  the  Law 
of  Gravitation  or  Mutual  Attraction. 

20.  Now  in  this  case  of  Mutual  Attraction,  we  have  no  opportunity 
of  witnessing  the  dofmant  condition  of  the  property  in  any  mass  of 
matter ;  for,  as  nothing  is  wanting  but  the  presence  of  another  mass  to 
call  this  property  into  operation,  it  is  always  generating  force,  and 
giving  rise  to  actions.  If  we  could  conceive  of  the  existence  of  but  a 
single  mass  of  matter  in  the  universe,  we  shall  at  once  see  that  though 
possessed  of  the  property  of  mutual  attraction,  it  would  not  be  able  to 
exercise  it,  so  as  to  generate  an  attractive  force,  or  to  produce  a  move- 
ment. 

21.  But  we  will  turn  to  another  case ;  in  which  there  is  a  closer 
analogy  to  the  condition  of  living  beings ;  and  by  which,  therefore,  the 
view  here  put  forth  may  be  more  clearly  illustrated.  When  a  magnet 
(itself  a  bar  of  iron,  having  no  peculiarity  of  appearance)  draws  towards 
it  a  piece  of  iron,  we  say  that  a  Magnetic  action  or  phenomenon  takes 
place ;  further,  we  speak  of  the  power  which  produced  the  movement, 
as  the  Magnetic  force  ;  and  we  attribute  this  force  to  a  certain  property 
inherent  in  the  Magnet,  by  virtue  of  which  it  draws  towards  itself  all 
pieces  of  iron  that  are  within  the  sphere  of  its  operation,  and  we  speak 
of  the  iron  bar  as  endowed  with  the  property  of  Magnetic  attraction. 
Now  we  cannot  ascertain  the  presence  or  absence  of  this  property  in  a 
certain  bar  of  iron,  by  any  difi*erence  in  its  aspect,  its  specific  gravity, 
its  chemical  properties,  nor,  in  fact,  by  any  other  mode  than  the  putting 
it  in  circumstances  adapted  to  call  the  Magnetic  property  into  action  if 
it  really  exist : — thus  we  dip  it  into  iron  filings,  and  judge  by  their  ad- 
hesion whether  it  is  capable  of  attracting  them ;  or,  as  a  still  more  deli- 
cate test,  we  ascertain  whether  it  is  capable  of  exerting  any  repulsive 
power  on  a  delicately-suspended  needle  already  magnetized.  Again,  a 
needle,  or  bar  of  iron,  which  exhibits  this  magnetic  power  of  attracting 
other  portions  of  the  same  metal,  exhibits  another  power,  which  would 
seem  at  first  sight  totally  distinct ;  namely,  that  of  constantly  turning 
one  of  its  extremities  towards  the  north,  and  the  other  towards  the  south, 
when  it  is  so  supported  as  to  be  free  to  do  so.     And  yet  there  is  no 


28  NATURE  AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

doubt  whatever,  that  this  directing  power  is  only  another  manifestation 
of  the  same  magnetic  attractiveness  ;  depending  on  the  relation  between 
the  magnetized  bar,  or  needle,  and  the  Earth,  which  must  itself  be  re- 
garded as  a  great  magnet.  Hence  the  idea  of  a  peculiar  kind  of  mutual 
attractiveness, — existing  in  only  a  limited  class  of  bodies,  capable  of  being 
excited  in  one  by  a  certain  agency  on  the  part  of  the  other,* — and  re- 
quiring for  its  exercise  or  manifestation  a  certain  set  of  conditions,  with- 
out which  no  phenomenon  results, — is  that  which  we  regard  as  funda- 
mental in  the  Science  of  Magnetism. 

22.  We  may  now  turn  from  these  departments  of  Physical  Science  to 
Chemistry ;  and  here  we  shall  find  that  the  investigation  is  carried  on 
upon  the  very  same  plan.  In  fact,  the  whole  science  of  Chemistry  is 
founded  upon  the  idea  of  a  certain  attractiveness  or  affinity  existing 
among  the  ultimate  particles  or  molecules  of  the  different  elementary 
substances  ;  and  therefore  entirely  distinct  from  the  homogeneous  attrac- 
tion, which  holds  together  the  particles  of  the  same  mass,  or  from  the 
gravitative  attraction,  which  operates  alike  upon  all  masses,  whatever  be 
their  composition.  Thus  we  say  that  Sulphuric  acid  and  Potash  have  an 
affinity  for  each  other;  because  they  unite  when  they  are  brought 
together,  and  form  a  new  compound.  This  is  a  Oftemical  action  or  phe- 
nomenon. Now  we  know  that  they  tend  to  unite  with  a  certain  force  ; 
a  force,  however,  which  cannot  be  measured  mechanically,  and  which 
can  only  be  expressed  by  comparing  it  with  some  other  force  of  the 
same  kind.  Thus  we  say  that  the  mutual  affinity  of  Sulphuric  acid  and 
Potash  is  greater  than  that  of  Nitric  acid  and  Potash ;  because,  if  we 
pour  Sulphuric  acid  upon  Nitrate  of  Potash,  the  Sulphuric  acid  detaches 
(as  it  were)  the  Potash  from  its  connexion  with  the  Nitric  acid,  forms  a 
new  compound  with  it,  and  sets  the  Nitric  acid  free.  Hence  we  say 
that  it  is  a  property  of  Sulphuric  acid  to  have  a  very  strong  affinity  for 
Potash.  This  property  exists  in  every  particle  of  Sulphuric  acid  that 
exists,  whether  free  or  combined ;  but  it  does  not  manifest  itself,  except 
when  called  into  operation  by  the  contact  of  Potash ;  and  it  then  de- 
velopes  a  force,  which  may  completely  change  the  combinations  previ- 
ously existing,  and  give  rise  to  new  ones. 

23.  Now  of  this  property  we  are  not  informed  by  any  of  the  other 
properties  of  Sulphuric  acid  ;  and  we  only  recognise  its  existence  by  the 
action  which  is  the  result  of  its  exercise.  If  a  new  element  or  com- 
pound be  discovered,  the  chemist  is  totally  unable  to  predict  its  force  of 
affinity  for  this  or  that  substance ;  and  he  can  only  guess  by  analogy, 
what  will  be  its  behaviour  under  various  circumstances.  Thus  if  it  have 
the  external  properties  of  a  Metal,  he  presumes  that  it  will  correspond 
with  the  Metals  in  possessing  a  strong  affinity  for  oxygen,  sulphur,  &c.; 
whilst  if  it  seem  analogous  to  Iodine,  Chlorine,  &c.,  he  infers  that  it  will 
be  a  supporter  of  combustion,  that  it  will  form  an  acid  with  hydrogen, 
and  so  on.  But,  even  though  such  guesses  may  be  made  with  a  certain 
amount  of  probability,  nothing  but  experience  can  show  the  positive 
degrees  of  affinity  which  the  substance  may  have  for  others  of  different 
kinds ;  and  the  experimental  determination  can  only  be  made,  by  observ- 

*  As  when  one  magnet  is  made  by  another;  or  when  iron  rails,  pokers,  &c.,  become 
magnetic  by  the  influence  of  the  earth. 


OF  VITAL  ACTIONS   IN  GENERAL.  2^ 

ing  the  actions  of  the  body  when  placed  in  different  circumstances,  from 
which  we  judge  of  its  properties^  and  of  the  forces  to  which  these  proper- 
ties give  rise  when  they  are  called  into  operation. 

24.  It  is  hoped  that  the  propriety  of  the  distinct  use  of  the  terms 
Vital  Action,  Vital  Force,  and  Vital  Property,  will  now  be  evident ; 
and  that  the  student  will  be  prepared  to  attach  distinct  ideas  to  each^f 
them.  It  is  the  business  of  the  Physiologist  to  study  those  actions  or 
phenomena,  which  are  peculiar  to  living  beings,  and  which  are  hence 
termed  vital: — he  endeavours  to  trace  them  to  the  operation  of  specific 
forces  acting  through  organized  structures,  just  as  the  Astronomer 
traces  all  the  movements,  regular  and  perturbed,  of  the  heavenly  bodies, 
to  the  mutual  attraction  of  their  masses,  acting  concurrently  with  their 
force  of  onward  rectilinear  movement ;  or  as  the  Chemist  attributes  the 
different  acts  of  combination  or  separation,  which  it  is  his  province  to 
study,  to  the  mutual  afiinities  of  the  substances  concerned : — and  the 
physiologist,  like  the  astronomer  or  the  chemist,  seeks  to  determine  the 
laws  according  to  which  these  forces  act,  or,  in  other  words,  to  express 
the  precise  conditions  under  which  they  are  called  into  play,  and  the 
actions  which  they  then  produce.  It  is  only  in  this  manner,  that  Phy- 
siology can  be  rightly  studied  and  brought  to  the  level  of  other  sciences. 
There  can  be  no  doubt  that  its  progress  has  been  greatly  retarded  by 
the  assumption,  that  its  phenomena  were  all  to  be  attributed  to  the 
operation  of  some  general  controlling  agency,  or  Vital  Principle ;  and 
that  the  laws  expressing  the  conditions  of  these  phenomena,  must  be 
sought  for  by  methods  of  investigation  entirely  distinct  from  those 
which  are  employed  in  other  sciences.  But  a  better  spirit  is  now  abroad; 
and  the  student  cannot  be  too  strongly  urged  to  discard  any  ideas  of 
this  kind  as  absolutely  untenable  ;  and  to  keep  steadfastly  in  view,  that 
the  laws  of  Vital  Action  are  to  be  attained  in  the  same  manner  as  those 
of  Physics  or  Chemistry, — that  is,  by  the  careful  collection  and  com- 
parison of  vital  phenomena,  and  by  applying  to  them  the  same  method 
of  reasoning,  as  that  which  is  used  in  determining  the  forces  and  pro- 
perties on  which  other  phenomena  depend.  True  it  is,  that  we  can 
scarcely  yet  hope  to  reach  the  same  degree  of  simplification,  as  that  of 
which  other  sciences  are  capable ;  and  this  on  account  of  the  very  com- 
plex nature  of  the  phenomena  themselves,  and  the  difiiculty  of  satisfac- 
torily determining  their  conditions.  The  uncertainty  of  the  results  of 
Physiological  experiments  is  almost  proverbial :  that  uncertainty  does 
not  result,  however,  from  any  want  of  fixity  in  the  conditions  under 
which  the  vital  forces  operate,  but  merely  from  the  influence  of  diffe- 
rences in  those  conditions,  apparently  so  slight  as  to  elude  observation, 
and  yet  sufiiciently  powerful  to  produce  an  entire  change  in  the  result. 
And,  owing  to  that  mutual  dependence  of  the  different  actions  of  the  orga- 
nized structure,  to  which  reference  has  been  already  made  (§  5),  we  cannot 
seriously  derange  one  class  of  these  actions,  without  also  deranging,  or 
even  suspending  others : — a  circumstance  which  obviously  renders  vital 
phenomena  much  more  difficult  of  investigation  than  those  of  inorganic 
matter. 

25.  All  sciences  have  their  "ultimate  facts  ;*'  that  is,  facts  for  which 
no  other  cause  can  be  assigned  than  the  Will  of  the  Creator.     Thus,  in 


30  NATURE   AND   OBJECTS   OP  PHYSIOLOGICAL   SCIENCE. 

Physics,  we  cannot  ascend  above  the  fact  of  Attraction  (which  operates 
according  to  a  simple  and  universal  law)  between  all  masses  of  matter ; 
and  in  Chemistry,  we  cannot  rise  beyond  the  fact  of  Affinity  (limited  by 
certain  conditions  which  are  not  yet  well  understood)  between  the  par- 
ticles of  different  kinds  of  matter.  When  we  say  that  we  have  explained 
any  phenomenon,  we  merely  imply  that  we  have  traced  its  origin  to 
properties  with  which  we  were  previously  acquainted,  and  shown  that  it 
takes  place  in  accordance  with  the  known  laws  of  their  operation.  Of 
the  existence  of  the  properties,  and  the  determination  of  the  conditions 
of  their  action,  we  can  give  no  other  account,  than  that  the  Creator 
willed  them  so  to  be ;  and,  in  looking  at  the  vast  variety  of  phenomena 
to  which  they  give  rise,  we  cannot  avoid  being  struck  with  the  general 
harmony  that  exists  amongst  them,  and  the  mutual  dependence  and 
adaptation  that  may  be  traced  between  them,  when  they  are  considered 
as  portions  of  the  general  economy  of  Nature.  There  is  no  difference 
in  this  respect  between  Physiology  and  other  sciences  ;  except  that  the 
number  of  these  (apparently)  ultimate  facts  is  at  present  greater  in 
physiology  than  it  is  in  other  departments,  because  we  are  not  at  present 
able  to  include  them  all  under  any  more  general  expression.  But,  as 
will  presently  appear,  a  considerable  degree  of  simplification  appears 
practicable  in  our  view  of  them ;  and  although  we  may  not  be  able  to 
say  why  the  structure  called  Muscular  should  possess  contractility,  and 
why  the  structure  called  Nervous  should  be  capable  of  generating  and 
conveying  the  force  which  excites  that  contractility  to  action,  we  may 
draw,  from  the  study  of  the  conditions  under  which  they  respectively 
manifest  themselves,  some  indications  of  the  existence  of  a  common  tie, 
such  as  that  which  binds  together  the  planetary  masses,  at  the  same 
time  that  it  weighs  down  the  bodies  on  the  surface  of  the  earth  towards 
its  centre. 

26.  In  the  study  of  any  branch  of  science,  it  is  most  desirable  to  com- 
mence with  definite  views  of  the  nature  of  the  phenomena  with  which  it 
is  concerned ;  and  such  are  best  gained  by  the  examination  of  these 
phenomena  under  their  simplest  aspects.  This  course  is  most  especially 
necessary  in  Physiology :  since  the  complexity  of  the  conditions  under 
which  its  phenomena  usually  present  themselves,  often  tends  to  mask 
their  real  character,  causing  that  to  be  regarded  as  essential  which  is 
only  accidental  or  contingent,  and  vice  versd.  It  is  extremely  difficult, 
however,  and  frequently  impossible,  for  the  Physiologist  to  isolate  these 
several  conditions,  and  to  study  them  separately,  in  the  way  that  the 
Chemical  or  Physical  investigator  would  do ;  and  his  best  course  is  to 
take  advantage  of  those  "experiments  ready  prepared  by  Nature," 
which  he  finds  in  the  variety  of  forms  of  living  organized  beings,  with 
which  the  globe  is  so  richly  peopled.  Now  it  is  in  the  simplest  forms  of 
Cryptogamic  Vegetation,  that  the  phenomena  of  Life  present  themselves 
under  their  least  complicated  aspect ;  for  we  shall  find  in  the  operations 
of  each  of  the  simple  cells  of  which  such  Plants  are  composed  (all  of 
them  resembling  one  another  in  structure  and  actions),  an  epito7ne,  as  it 
were,  of  those  of  the  highest  and  most  complex  Plant ;  whilst  those  of 
the  higher  Plants  bear  a  close  correspondence  with  those  which  are 
immediately  concerned  in  the  Nutrition  and  Reproduction  of  the  Animal 


OP  VITAL   ACTIONS   IN   GENERAL.  31 

body.  And  when  we  come  to  consider  the  proper  Animal  functions,  we 
shall  find  that  they  are  not  so  far  removed  in  their  essential  nature  from 
those  of  Plants,  but  that  they  may  be  ranked  under  the  same  category, 
and  regarded  as  diflferent  manifestations  of  the  same  original  forces. 
A  Qell^  then,  in  Physiological  language,  is  a  closed 

vesicle  or  minute  bag,  formed  by  a  membrane  in  ^ig-  1-      

which  no  definite  structure  can  be  discerned,  and 
having  a  cavity  which  may  contain  matters  of  varia- 
ble consistence.  Such  a  cell  constitutes  the  whole 
organism  of  such  simple  plants  as  the  Protococcus 
nivalis  ('  red  snow'),  or  Palmella  eruenta  ('  gory 
dew') ;  for  although  the  patches  of  this  kind  of  vege- 
tation, which  attract  our  notice,  are  made  up  of  vast 
aggregations  of  such  cells,  yet  they  have  no  depen- 
dence upon  one  another,  and  the  actions  of  each  are  J^-p^«  i'°l?dtt"f 'mX 
an  exact  repetition  of  those  of  the  rest.  In  such  cuies. 
a  cell,  every  organized  fabric,  however  com- 
complex,  originates.  The  vast  tree^  almost  a  forest  in  itself,  and  the 
feeling,  thinking,  intelligent  man^  spring  from  a  germ,  that  differs  in  no 
obvious  particular  from  the  permanent  condition  of  one  of  these  lowly 
beings.  But  whilst  the  powers  of  the  latter  are  restricted,  as  we  shall 
see,  to  the  continual  multiplication  of  new  and  distinct  individuals  like 
itself,  those  of  the  former  enable  it  to  produce  new  cells  that  remain  in' 
closer  connexion  with  each  other ;  and  these  are  gradually  converted, 
by  various  transformations  of  their  own,  into  the  diversified  elements  of 
a  complex  fabric.  The  most  highly-organized  being,  however,  will  be 
shown  to  consist  in  great  part  of  cells  that  have  undergone  no  such  trans- 
formation, amongst  which  the  different  functions  performed  by  the  indi- 
vidual in  the  case  just  cited,  are  distributed,  so  to  speak ;  so  that  each 
cell  has  its  particular  object  in  the  general  economy,  whilst  the  history 
of  its  own  life  is  essentially  the  same  as  if  it  were  maintaining  a  separate 
existence. 

27.  We  shall  now  examine,  then,  the  history  of  the  solitary  cell  of 
one  of  the  simplest  Cryptogamic  Plants,  from  its  first  development  to 
its  final  decay  ;  in  other  words,  we  shall  note  those  Vital  Phenomena, 
which  are  as  distinct  from  those  of  any  inorganic  body,  as  is  its  organ- 
ized structure  (simple  as  it  appears)  from  the  mere  aggregation  of  par- 
ticles in  a  mineral  mass.  In  the  first  place,  the  cell  takes  its  origin 
from  a  germ,  which  may  be  a  minute  molecule,  that  cannot  be  seen 
without  a  microscope  of  high  power.*  This  molecule  appears,  in  its 
earliest  condition,  to  be  a  simple  homogeneous  particle,  of  spherical 
form  ;  but  it  gradually  increases  in  size  ;  and  a  distinction  becomes 
apparent  between  its  transparent  exterior  and  its  coloured  interior. 
Thus  we  have  the  first  indication  of  the  cell-wall,  and  the  cavity.  As 
the  enlargement  proceeds,  the  distinction  becomes  more  obvious ;  the 
cell-wall  is  seen  to  be  of  extreme  tenuity  and  perfectly  transparent,  and 
to  be  homogeneous  in  its  texture ;  whilst  the  contents  of  the  cavity  are 

*  The  modes  in  which  new  cells  may  be  generated  are  various  ;  but  the  above  exam- 
ple is  purposely  drawn  from  one  of  those  simple  Algee,  whose  usual  mode  of  multipli- 
cation is  by  ♦*  zoospores."     (See  the  Author's  "  Principles  of  Physiology,"  U  139-144.) 


82  NATURE   AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

distinguished  by  their  colour,  which  is  very  commonly  either  green  or 
crimson.  At  first  they,  too,  appear  to  be  homogeneous ;  but  a  finely- 
granular  appearance  is  then  perceptible ;  and  a  change  gradually  takes 
place,  which  seems  to  consist  in  the  aggregation  of  the  minute  granules 
into  molecules  of  more  distinguishable  size  and  form.  These  molecules, 
which  are  the  germs  of  new  cells,  seem  to  be  at  first  attached  to  the 
wall  of  the  parent  cell;  afterwards  they  separate  from  it,  and  move 
about  in  its  cavity ;  and  at  a  later  period,  the  parent-cell  bursts  and 
sets  them  free.  Now,  this  is  the  termination  of  the  life  of  the  parent 
cell ;  but  the  commencement  of  the  life  of  a  new  brood ;  since  every  one 
of  these  germs  may  become  developed  into  a  cell,  after  precisely  the 
foregoing  manner,  and  will  then  in  its  turn  multiply  its  kind  by  a  simi- 
lar process. 

28.  By  reasoning  upon  the  foregoing  history,  we  may  arrive  at  cer- 
tain conclusions,  which  will'  be  found  equally  applicable  to  all  living 
beings.  In  the  first  place,  the  cell  originates  in  a  germ  or  reproductive 
body,  which  has  been  prepared  by  another  similar  cell  that  previously 
existed.  There  is  no  sufficient  reason  to  believe  that  there  is  any  ex- 
ception to  this  rule.  So  far  as  we  at  present  know,  every  Plant  and 
every  Animal  is  the  ofispring  of  a  parent,  to  which  it  bears  a  resemblance 
in  all  essential  particulars ;  and  the  same  may  be  said  of  the  individual 
cells,  of  which  the  Animal  and  Vegetable  fabrics  are  composed.  But 
how  does  this  germ,  this  apparently  homogeneous  molecule,  become  a 
cell  ?  The  answer  to  this  is  only  to  be  found  in  its  peculiar  property, 
of  drawing  materials  to  itself  from  the  elements  around,  and  of  incorpo- 
rating these  with  its  own  substance.  The  Vegetable  cell  may  grow 
wherever  it  can  obtain  a  supply  of  water,  carbonic  acid,  and  ammonia ; 
for  these  compounds  supply  it  with  oxygen,  hydrogen,  carbon,  and  nitro- 
gen, in  the  state  most  adapted  for  the  exercise  of  the  combining  power, 
by  which  it  converts  them  into  those  new  compounds,  whose  properties 
adapt  them  to  become  part  of  the  growing  organized  fabric.  Here,  then, 
we  have  two  distinct  operations ; — the  union  of  these  elementary  sub- 
stances into  that  composite  protoplasma,  which  seems  to  be  the  imme- 
diate pabulum  of  the  Vegetable  tissues  ; — and  the  incorporation  of  that 
product  with  the  substance  of  the  germ  itself. 

29.  The  first  of  these  changes  mai/  be,  and  probably  is,  of  a  purely 
Chemical  nature ;  and  analogous  cases  are  not  wanting,  in  the  pheno- 
mena of  Inorganic  Chemistry,  in  which  one  body.  A,  exerts  an  influence 
upon  two  other  bodies,  B  and  c,  so  as  to  occasion  their  separation  or 
their  union,  without  itself  undergoing  any  change.  Thus  platinum,  in 
a  finely-divided  state,  will  cause  the  union  of  oxygen  and  hydrogen  at 
ordinary  temperatures ;  and  finely-powdered  glass  will  do  the  same  at 
the  temperature  of  572°.  This  kind  of  action  is  called  catalysis.  A 
closer  resemblance,  perhaps,  is  presented  by  the  act  oi  fermentation  ;  in 
which  a  new  arrangement  of  particles  takes  place  in  a  certain  compound, 
by  the  presence  of  another  body  which  is  itself  undergoing  change,  but 
which  does  not  communicate  any  of  its  elements  to  the  new  products. 
Thus,  if  a  small  portion  of  animal  membrane,  in  a  certain  stage  of  de- 
composition, be  placed  in  a  solution  of  sugar,  it  will  occasion  a  new 
arrangement  of  its  elements,  which  will  generate  two  new  products, 


OF  VITAL  ACTIONS   IN   GENERAL.  33 

alcohol  and  carbonic  acid.  If  the  decomposition  of  the  membrane  have 
proceeded  further,  a  dijQTerent  product  will  result ;  for  instead  of  alcohol, 
lactic  acid  will  be  generated.  And  in  a  further  stage  of  decomposition, 
the  ferment  is  the  means  of  producing  butyric  acid  (the  fatty  acid  of 
butter).  There  appears  no  improbability,  then,  in  the  idea,  that  the 
influence  exerted  by  the  germinal  molecule  is  of  an  analogous  nature ; 
and  that  it  operates  upon  the  elements  of  the  surrounding  water  ahd^ 
carbonic  acid,  according  to  purely  chemical  laws,  uniting  the  carbon 
with  the  elements  of  water,  and  setting  free  the  oxygen.  This  result  of 
the  nutritive  operations  of  the  simpl§  cellular  plants  may  be  easily  veri- 
fied experimentally,  by  exposing  the  green  scum,  which  floats  upon 
ponds,  ditches,  &c.,  and  which  consists  of  the  cells  of  a  minute  Crypto- 
gamic  Plant,  to  the  influence  of  light  and  warmth  beneath  a  receiver ; 
it  is  found  that  oxygen  is  then  liberated,  by  the  decomposition  of  the 
carbonic  acid  contained  in  the  water.  We  shall  presently  have  to  return 
to  the  consideration  of  the  Chemical  phenomena  of  living  beings ;  and 
shall  pass  on,  therefore,  to  consider  those  to  which  no  such  explanation 
applies. 

30.  The  second  stage  in  the  nutritive  process  consists  in  the  appro- 
priation of  the  new  products  thus  generated  to  the  enlargement  of  the 
living  cell-structure ;  a  phenomenon  obviously  distinct  from  the  pre- 
ceding. It  is  well  to  observe,  that  this  process,  which  constitutes  the 
act  of  Orgamzatio7i,  may  be  clearly  distinguished  in  the  higher  Plants 
and  Animals,  as  consisting  of  two  stages  ; — the  first  of  these  being  that 
of  assimilation,  which  consists  in  the  further  preparation  or  elaboration 
of  the  fluid  matter,  by  certain  alterations  whose  nature  is  not  yet  clear, 
so  as  to  render  it  plastic  or  organizahle  ; — the  second  being  the  act  of 
formation,  or  the  conversion  of  the  organizable  matter  into  the  solid 
texture,  in  which  process  the  properties  that  distinguish  that  texture 
come  to  manifest  themselves.  Thus,  for  example,  we  do  not  find  that 
a  solution  of  dextrin  (or  starch-gum)  is  capable  of  being  at  once  applied 
to  the  development  of  Vegetable  tissue,  although  it  is  identical  in  com- 
position with  cellulose ;  for  it  must  first  pass  through  a  stage,  in  which 
it  possesses  a  peculiar  glutinous  character,  and  exhibits  a  tendency  to 
spontaneous  coagulation,  that  seems  like  an  attempt  at  the  production 
of  organic  forms.  And  in  like  manner,  the  albumen  of  Animals  is  evi- 
dently not  capable  of  being  applied  to  the  nutrition  of  the  fabric,  until 
it  has  been  first  converted  into  fibrin  ;  which  also  is  distinguished  by  its 
tenacious  character,  by  its  spontaneous  coagulability,  and  by  the  fibrous 
structure  of  its  clot.  Now,  in  both  these  cases,  there  is  probably  some 
slight  modification  in  chemical  composition,  that  is,  in  the  proportions 
of  the  ultimate  elements  ;  but  the  principal  alteration  is  evidently  that 
which  is  eff'ected  by  the  rearrangement  of  the  constituent  particles ;  so 
that,  without  any  considerable  change  in  their  proportions,  a  compound 
of  a  very  diff"erent  nature  in  generated.  Of  the  possibility  of  such 
changes  we  have  abundant  illustrations  in  ordinary  Chemical  pheno- 
mena ;  for  there  is  a  large  class  of  substances,  termed  isomeric,  which, 
with  an  identical  composition,  possess  chemical  and  physical  properties 
of  a  most  diverse  character. 

31.  But  we  cannot  attribute  the  production  of  Fibrin  from  Albumen, 

3 


34  NATURE  AND   OBJECTS  OF   PHYSIOLOGICAL   SCIENCE. 

the  organizable  from  the  unorganizable  material,  to  the  simple  operation 
of  the  same  agencies  as  those  which  determine  the  production  of  the 
different  isomeric  compounds ;  for  the  properties  of  Fibrin  are  much 
more  vitally  distinct  from  those  of  Albumen,  than  they  are  either  che- 
mically ov  physically ;  that  is,  we  find  in  the  one  an  incipient  manifes- 
tation of  Life^  of  which  the  other  shows  no  indications.  The  spontane- 
ous coagulation  of  fibrin,  which  takes  place  very  soon  after  it  has  been 
withdrawn  from  the  vessels  of  the  living  body,  is  a  phenomenon  to  which 
nothing  analogous  can  be  found  elsewhere ;  for  it  has  been  clearly  shown 
not  to  be  occasioned  by  any  mere  physical  or  chemical  change  in  its 
constitution ;  and  it  takes  place  in  a  manner  which  indicates  that  a  new 
arrangement  of  particles  has  been  effected  in  it,  preparatory  to  its  being 
converted  into  a  living  solid.  For  this  coagulation  is  not  the  mere  ho- 
mogeneous setting^  which  takes  place  in  a  solution  of  gelatine  in  cooling ; 
nor  is  it  the  aggregation  of  particles  in  a  mere  granular  state  (closely 
resembling  that  of  a  chemical  precipitate),  which  takes  place  in  the 
coagulation  of  albumen :  it  is  the  actual  production  of  a  simple  fibrous 
tissue^  by  the  union  of  the  particles  of  fibrin  in  a  determinate  manner, 
bearing  a  close  resemblance  to  the  similar  process  in  the  living  body 
(§  188).  We  say,  then,  that  the  coagulation  of  Fibrin,  and  the  produc- 
tion of  a  fibrous  tissue,  are  the  manifestation  of  its  vital  properties, 
rather  than  the  direct  result  of  chemical  or  physical  agencies ;  because 
no  substance  is  known  to  perform  any  such  actions,  without  having  been 
subjected  to  the  influence  of  a  living  body ;  and  because  the  actions 
themselves  are  altogether  different  from  any  which  we  witness  else- 
where. 

32.  The  act  of  Formation  seems  to  consist  of  a  continuation  of  the 
same  kind  of  change, — that  is,  a  new  arrangement  of  the  particles,  pro- 
ducing substances  which  differ  both  as  to  structure  and  properties  from 
the  materials  employed,  but  which  may  be  so  closely  allied  to  them  in 
chemical  composition,  that  the  difference  cannot  be  detected.  Thus, 
from  the  "  protoplasma"*  of  Plants  are  generated,  in  the  process  of  cell- 
development,  the  membranes  which  constitute  the  walls  of  the  cells: 
chemically  speaking,  there  seems  to  be  no  essential  distinction  between 
these  substances  ;  and  yet  between  the  living,  growing,  reproducing  cell, 
and  the  gelatinous,  semifluid  matter  in  which  they  are  imbedded,  how 
wide  the  difference  !  So  in  the  Animal  body,  we  find  that  the  composi- 
tion of  the  proper  muscular  tissue  scarcely  differs,  in  regard  to  the  pro- 
portion of  its  elements,  from  the  fibrin,  or  even  from  the  albumen,  of 
the  blood ;  and  yet  what  an  entire  rearrangement  must  take  place  in 
the  particles  of  either,  before  a  tissue  so  complex  in  structure,  and  so 
peculiar  in  properties,  as  muscular  fibre,  can  be  generated ! 

33.  Both  in  the  Plant  and  the  Animal,  we  find  that  tissues  presenting 
great  diversities  both  in  structure  and  properties,  may  take  their  origin 
in  the  same  organizable  material ;  but  in  every  case  (at  least  in  the 
ordinary  processes  of  growth  and  reparation)  the  new  tissue  of  each 
kind  is  formed  in  continuity  with  that  previously  existing.     Thus  in 

*  This  term  is  now  commonly  employed  to  designate  that  combination  of  starchy  and 
albuminous  matters,  in  which  all  newly-forming  cells  appear  to  originate.     See  g  28. 


OF  VITAL   ACTIONS   IN   GENERAL.  35 

the  stem  of  a  growing  tree,  from  the  very  same  glutinous  sap  or  cam- 
bium, intervening  between  the  wood  and  the  bark,  the  wood  generates, 
in  contact  with  its  last-formed  layer,  a  new  cylinder  of  wood ;  whilst 
the  bark  produces  in  contact  with  its  last-formed  layer,  a  new  cylinder 
of  bark ;  the  woody  cylinder  being  characterized  by  the  predominance 
of  ligneous  fibre  and  ducts,  and  the  cortical  by  the  predominance_of_ 
cellular  tissue.  In  like  manner  we  find  that,  in  animals,  muscle  pro- 
duces muscle,  bone  generates  bone,  nerve  developes  nerve,  in  continuity 
with  itself,  all  at  the  expense  of  the  materials  supplied  by  the  very  same 
blood. 

34.  The  Nutrition  of  tissues,  by  the  organization  of  the  materials 
contained  in  the  nutrient  fluid  with  which  they  are  supplied,  may  be 
superficially  compared,  therefore,  to  the  act  of  crystallization,  when  it 
takes  place  in  a  mixed  solution  of  two  or  more  salts.  If  in  such  a  solu- 
tion we  place  small  crystals  of  the  salts  it  contains,  these  crystals  will 
progressively  increase  by  their  attraction  for  the  other  particles  of  the 
same  kind,  which  were  previously  dissolved ;  each  crystal  attracting  the 
particles  of  its  own  salt,  and  exerting  no  influence  over  the  rest.  And 
it  is  curious  that  if  either  of  the  crystals  be  broken,  the  new  deposit 
will  take  place  upon  it  in  such  a  mode  as  gradually  to  reproduce  its 
characteristic  form.  But  it  must  be  borne  in  mind,  that  such  a  resem- 
blance goes  no  further  than  the  surface ;  for  the  growth  of  a  crystal 
cannot  be  really  regarded  as  in  the  least  analogous  to  that  of  a  cell. 
The  crystal  progressively  increases  by  the  deposit  of  particles  upon  its 

^'exterior ;  the  interior  undergoes  no  change ;  and  whatever  may  be  the 
size  it  ultimately  attains,  its  properties  remain  precisely  the  same  as 
those  of  the  original  nucleus.  On  the  other  hand,  the  cell  grows  from 
its  original  germ  by  a  process  of  iifterstitial  deposit ;  the  substance  of 
which  its  wall  is  composed  extends  itself  in  every  part ;  and  the  new 
matter  is  completely  incorporated  with  the  old. 

35.  Moreover,  as  the  increase  proceeds,  we  see  an  evident  distinction 
between  the  cell-wall  and  its  cavity ;  and  we  observe  that  the  cavity  is 
occupied  by  a  peculiar  matter,  different  from  the  substance  of  the  cell- 
wall,  though  obviously  introduced  through  it.     Of  the  essential  differ- 
ence which  may  exist  in  composition,  between  the  cell-wall  and  the  con- 
tents of  the  cavity,  we  have  a  remarkable  example  in  the  case  of  the 
simple  Cryptogamic  plant,  which  constitutes  Yeast,  and  which  differs  in 
no  essential  part  of  the  history  of  its  growth  from  the  examples  already 
referred  to.    The  principal  component  of  its  cell- walls  is  nearly  identical 
with  ordinary  cellulose  f  whilst  the  contents  of  the  cells  are  closely 
allied  in  composition  to  proteine.     Again,  in  the  fat-cells  of  Animals, 
the  cell-wall  is  formed  from  a  proteine  compound ;  whilst  the  oily  con- 
tents agree,  in  the  absence  of  nitrogen,  and  in  their  general  chemical 
relations,  with  the  materials  of  the  tissues  of  Plants.     It  is  evident, 
then,  that  one  of  the  inherent  powers  of  the  cell,  is  that  by  which  it  not 
only  combines  the  surrounding  materials  into  a  substance  adapted  for 
the  extension  of  its  wall,  but  that  which  enables  it  to  exercise  a  similar 
combining  power  on  other  materials  derived  from  the  same  source,  and 
to  form  a  compound, — of  an  entirely  different  character,  it  may  be, — 
which  occupies  its  cavity.     Now  this  process  is  as  essential  to  our  idea 


86  NATURE  AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

of  a  living  cell,  as  is  the  growth  of  its  wall ;  and  it  must  never  be  left 
out  of  view,  when  considering  the  history  of  its  development. 

36.  Every  kind  of  cell  has  its  own  specific  endowments ;  and  gene- 
rates in  its  interior  a  compound  peculiar  to  itself.  The  nature  of  this 
compound  is  much  less  dependent  upon  the  nutrient  materials  which 
are  supplied  to  the  cell,  than  upon  the  original  inherent  powers  of  the 
cell  itself,  derived  from  its  germ.  Thus  we  find  that  the  "red  snow" 
and  "  gory  dew"  invariably  form  a  peculiar  red  secretion ;  and  that  they 
will  only  grow  where  they  can  obtain,  from  the  air  and  moisture  around, 
the  elements  of  that  secretion.  Again,  the  "yeast-plant"  invariably 
forms  a  secretion  analogous  to  animal  proteine ;  and  it  will  only  grow 
in  a  fluid  which  supplies  it  with  the  materials  of  that  substance.  Hence 
the  "red  snow"  would  not  grow  in  a  fermentible  saccharine  fluid;  nor 
would  the  "yeast  plant"  vegetate  on  damp  cold  surfaces.  Yet  there  is 
little  difference,  if  any,  between  their  cell-walls,  in  regard  to  chemical 
composition. — So,  also,  we  shall  find  hereafter,  that  one  set  of  cells  in 
the  Animal  body  will  draw  into  themselves,  during  the  process  of  growth, 
the  elements  of  bile ;  another,  the  elements  of  milk ;  another,  fatty 
matter ;  and  so  on  :  the  peculiar  endowments  of  each  being  derived  from 
their  several  germs,  which  seem  to  have  an  attraction  for  these  sub- 
stances respectively,  and  which  thus  draw  them  together ;  whilst  the 
cell-wall  appears  to  have  a  uniform  composition  in  all  instances. 

37.  The  term  Secretion^  or  setting  apart,  is  commonly  applied  to  this 
operation,  to  distinguish  it  from  Nutrition  or  growth ;  but  it  is  obvious 
from  what  has  now  been  stated,  that  the  act  of  secretion  is  in  reality 
the  increase  or  growth  of  the  cell-contents,  just  as  the  process  of  en- 
largement is  the  increase  or  growth  of  the  cell-wall ;  and  that  the  two 
together  make  up  the  whole  proce^  of  Nutrition,  which  cannot  be  pro- 
perly understood,  unless  both  are  taken  into  account.  It  is  to  be  remem- 
bered, however,  that  the  contents  of  the  cell  may  not  be  destined  to 
undergo  organization ;  indeed  we  shall  find  hereafter,  that  the  main  use 
of  certain  cells  is  to  draw  off  from  the  circulating  fluid  such  materials 
as  are  incapable  of  organization ;  and  the  operation  may  be  so  far  attri- 
buted, therefore,  to  the  agency  of  Chemical  forces.  But  we  shall  find 
that,  in  other  instances,  the  cell-contents  are  destined  to  undergo  orga- 
nization, and  this  either  within  the  parent  cell,  or  after  they  leave  it ; 
here,  then,  we  must  recognise  a  distinct  vitalizing  agency,  as  exerted 
by  the  cell  upon  its  contents. 

38.  This  organizing  or  vitalizing  influence  must  be  exerted  upon  a 
certain  portion  of  the  contents  of  every  cell  that  is  capable  of  repro- 
ducing itself;  for  it  is  in  this  manner  that  those  germs  are  produced,  in 
which  all  the  wonderful  properties  are  inherent,  that  are  destined  to 
manifest  themselves,  when  they  are  set  free  from  the  parent-cell.  This 
power  of  Reproduetio7i  is  one  of  those,  which  most  remarkably  distin- 
guishes the  living  being ;  and  we  shall  find  that,  in  the  highest  Animal, 
as  in  the  humblest  Plant,  it  essentially  consists  in  the  preparation  of  a 
cell-germ,  which,  when  set  free,  gradually  developes  itself  into  a  struc- 
ture like  that  from  which  it  sprang.  The  reproductive  molecules  or 
cell-germs  are  formed,  like  the  tissue  and  the  contents  of  the  parent-cell, 
from  the  nutrient  materials  which  it  has  the  power  of  bringing  together 


I 


OP  VITAL   ACTIONS   IN   GENERAL.  37 

and  combining ;  and  in  their  turn  they  pass  through  a  corresponding 
series  of  changes ;  and  at  length  produce  a  new  generation  of  similar 
molecules,  by  which  the  race  is  destined  to  be  continued.  Notwith- 
standing the  mystery  which  has  been  supposed  to  attach  itself  to  this 
process,  it  is  obvious  that  there  is  nothing  in  reality  more  difficult  to 
understand  in  the  fact,  that  the  parent-cell  organizes  and  vitalizes  the 
protoplasma  which  it  has  elaborated,  so  that  it  should  form  the  germ  of 
a  new  individual  possessing  similar  properties  with  itself;  than  in  its 
incorporating  the  same  material  with  its  own  structure,  and  causing  it 
to  take  a  share  in  its  own  actions. 

39.  Finally,  the  parent-cell  having  arrived  at  its  full  development, 
having  passed  through  the  whole  series  of  changes  which  is  character- 
istic of  the  species,  and  having  prepared  the  germs  by  which  the  race 
is  to  be  propagated,  dies  and  decays ; — that  is,  all  those  operations, 
which  distinguish  living  organized  structures  from  inert  matter,  cease 
to  be  performed ;  and  it  is  given  up  to  the  influence  of  chemical  forces 
only,  which  speedily  occasion  a  separation  of  its  elements,  and  cause 
them  to  return  to  their  original  forms,  namely,  water,  carbonic  acid, 
and  ammonia.  It  is  not,  however,  in  the  dead  organism  alone  that  this 
decomposition  occurs ;  for  it  is  certain  that  interstitial  death  and  decay 
are  incessantly  taking  place  during  the  whole  life  of  the  being ;  and  that 
the  maintenance  of  its  healthy  or  normal  condition  depends  upon  the 
constant  removal  of  the  products  of  that  decay,  and  upon  their  continual 
replacement.  If,  on  the  one  hand,  those  products  be  retained,  they  act 
in  the  manner  of  poisons  ;  being  quite  as  injurious  to  the  welfare  of  the 
body,  as  the  most  deleterious  substances  introduced  from  without.  On 
the  other  hand,  if  they  be  duly  carried  off,  but  be  not  replaced,  the 
conditions  essential  to  vital  action  are  not  fulfilled,  and  the  death  of  the 
organism  must  be  the  result. 

40.  Now  it  is  to  be  observed  that,  as  Plants  obtain  the  chief  materials 
of  their  growth  from  water  and  carbonic  acid,  taking  the  carbon  from 
the  latter  and  setting  free  the  oxygen,  so  do  they  require,  as  the  condi- 
tion for  their  decay,  the  presence  of  oxygen,  which  may  reunite  with  the 
carbon  that  is  to  be  given  back  to  the  atmosphere.  If  secluded  from 
this,  the  vegetable  tissues  may  be  preserved  for  a  long  time  without 
decomposition.  Generally  speaking,  indeed,  they  are  not  prone  to  rapid 
decay,  except  at  a  high  temperature ;  and  hence  it  is  that  we  have  so 
little  evidence,  in  Plants,  of  the  constant  interstitial  change,  of  which 
mention  has  just  been  made.  Its  existence,  however  (at  least  in  all  the 
softer  portions  of  the  structure),  is  made  evident  by  the  fact,  that  a  con- 
tinual extrication  of  carbonic  acid  takes  place,  to  an  amount  which 
sometimes  nearly  equals  that  of  the  carbonic  acid  decomposed,  and  of 
the  oxygen  set  free,  in  the  act  of  Nutrition  (§  28).  The  latter  operation 
is  only  effected  under  the  stimulus  of  sunlight ;  the  former  is  constantly 
going  on,  by  day  and  by  night,  in  sunshine  and  in  shade ;  and  if  it  be 
impeded  or  prevented  by  want  of  a  due  supply  of  oxygen,  the  plant 
speedily  becomes  unhealthy.  Now  this  extrication  of  the  products  of 
interstitial  decay  is  termed  Excretion.  It  is  usually  confined  in  Plants 
to  the  formation  of  carbonic  acid  and  water,  by  the  union  of  the  particles 
of  their  tissues  with  the  oxygen  of  the  air, — a  process  identical  with 


38  NATURE   AND    OBJECTS    OF   PHYSIOLOGICAL   SCIENCE. 

that  which  occurs  after  the  death  of  the  entire  structure.  But  in  Ani- 
mals it  is  much  more  complicated ;  owing  to  the  larger  number  of  con- 
stituents in  their  fabric,  and  to  the  much  greater  variety  in  the  propor- 
tions in  which  these  are  combined ;  hence  the  products  of  interstitial 
decomposition  are  much  more  numerous  and  varied,  and  several  distinct 
modes  are  devised  for  getting  rid  of  them.  Moreover,  as  the  animal 
tissues  are  much  further  removed  than  the  Vegetable  from  the  composi- 
tion of  Inorganic  bodies,  they  are  subject  to  much  more  rapid  and  con- 
stant decay ;  and  we  shall  find  that  this  decay  is  so  considerable  in 
amount,  as  to  require  on  the  one  hand  a  very  complex  excretory  appa- 
ratus to  carry  off  the  disintegrated  matter,  and  on  the  other  a  large 
supply  of  nutrient  materials  to  replace  it. 

41.  The  preceding  history  may  be  thus  summed  up.  i.  The  Vege- 
table cell-germ  or  reproductive  molecule  draws  to  itself,  and  combines 
together,  certain  inorganic  elements ;  and  thereby  produces  a  new  and 
peculiar  compound.  This  compound,  however,  exhibits  no  properties  that 
distinguish  it  from  others,  in  which  ordinary  Qhemical  agencies  have 
been  concerned ;  and  we  may,  therefore,  regard  the  first  act  of  the  cell- 
germ  as  of  a  purely  chemical  nature.  We  shall  presently  see  that  che- 
mical agencies  are  undoubtedly  concerned  in  it,  to  a  very  considerable 
degree.  The  Animal  cell-germ  does  not  possess  the  same  Chemical 
power ;  it  is  not  capable  of  decomposing  the  water,  carbonic  acid,  and 
ammonia,  which  include  the  elements  of  its  tissues ;  and  it  is  entirely 
dependent  for  its  growth,  upon  the  supply  of  nutriment  previously  pre- 
pared for  it  by  the  agency  of  the  vegetable  kingdom,  many  species  of 
which  possess  the  power  of  generating  a  large  amount  of  proteine-com- 
pounds  within  their  cells,  though  they  do  not  organize  them.  ii.  The 
cell -germ  then  exerts  an  Assimilating  agency  upon  the  pabulum  thus 
prepared ;  by  which  a  new  arrangement  of  its  particles  is  produced. 
This  new  arrangement  gives  new  and  peculiar  qualities  to  the  fluid, 
which  show  that  it  is  something  more  than  a  mere  chemical  compound, 
and  that  it  is  in  the  act  of  undergoing  the  process  of  organization,  ill. 
The  Formation  of  this  elaborated  pabulum  into  tissue  then  takes  place ; 
its  materials  are  withdrawn  from  the  fluid,  and  incorporated  with  the 
solid  texture ;  and  in  thus  becoming  part  of  the  organized  fabric,  they 
are  caused  to  exhibit  its  own  peculiar  properties.  IV.  At  the  same 
time,  another  portion  of  this  pabulum  is  gradually  prepared  to  serve  as 
the  germ  of  a  new  cell,  or  set  of  cells,  by  which  the  same  properties  are 
to  be  exhibited  in  another  generation,  v.  By  an  operation  resembling 
that  concerned  in  the  first  preparation  of  the  pabulum,  certain  products, 
more  or  less  differing  from  it  in  character,  but  not  destined  to  undergo 
organization,  are  formed  in  the  cavity  of  the  cell.  vi.  A  decomposition 
or  disintegration  of  the  organized  structure  is  continually  going  on,  by 
the  separation  of  its  elements  into  simpler  forms,  under  the  influence  of 
purely  Chemical  agencies ;  and  the  setting  free  of  these  products  by  an 
act  of  excretion,  is  thus  incessantly  restoring  to  the  Inorganic  world  a 
portion  of  the  elements  that  have  been  withdrawn  from  it.  vii.  When 
the  term  of  life  of  the  parent-cell  has  expired,  and  its  reproductive 
molecules  are  prepared  to  continue  the  race,  the  actions  of  nutrition 
cease ;  those  of  decomposition  go  on  unchecked ;  and  the  death  of  the 


OF  VITAL   ACTIONS   IN   GENERAL.  39 

structure,  or  the  loss  of  its  distinguishing  vital  properties,  is  the  result. 
By  the  decomposition,  which  then  takes  place  with  increased  rapidity,  its 
elements  are  restored  to  the  Inorganic  world ;  presenting  the  very  same 
properties  as  they  did  when  first  withdrawn  from  it ;  and  becoming  capa- 
ble of  being  again  employed,  by  any  successive  numbers  of  living  beings, 
to  go  through  the  same  series  of  operations. 

42.  Thus,  then,  we  see  that  our  fundamental  idea  of  the  properdTes" 
of  the  simplest  Living  being  consists  in  this  ; — that  it  has  the  capability 
of  drawing  into  its  own  substance  certain  of  the  elements  furnished  by 
the  inorganic  world : — that  it  forms  these  into  new  combinations  (which 
the  chemist  may  find  out  methods  of  imitating) ; — that  it  rearranges  the 
particles  of  these  combinations,  in  that  peculiar  mode  which  we  call  or- 
ganization ; — that  in  producing  this  new  arrangement,  it  renders  them 
capable  of  exhibiting  a  new  set  of  properties,  which  we  call  vital,  and 
which  are  manifested  by  them,  either  as  connected  with  the  parent  or- 
ganism, or  as  appertaining  to  the  germs  of  new  structures,  according  to 
the  mode  in  which  the  materials  are  applied; — that,  notwithstanding  its 
peculiar  condition,  it  remains  subject  to  the  ordinary  laws  of  Chemistry, 
and  that  decomposition  of  its  structure  is  continually  taking  place ; — 
and  finally,  that  the  duration  of  its  vital  activity  is  limited ;  the  changes 
which  the  organic  structure  undergoes,  in  exhibiting  its  peculiar  actions, 
being  such  as  to  render  it  (after  a  longer  or  shorter  continuance  of 
them)  incapable  of  any  longer  performing  them. 

43.  There  is  abundant  evidence,  that  the  duration  of  the  Life,  or 
state  of  Vital  Activity,  of  an  organized  structure,  is  inversely  propor- 
tioned to  the  degree  of  that  activity ;  and  consequently  that  Life  is 
shortened  by  an  increased  or  abnormal  activity ;  whilst  it  may  often 
be  prolonged  by  influences  which  diminish  that  activity.  Thus,  we  shall 
hereafter  find  reason  to  believe,  that  the  duration  of  life  in  the  Muscular 
and  Nervous  tissues  of  Animals  is  entirely  dependent  upon  the  degree 
in  which  they  are  exercised ;  every  call  upon  their  activity  causing  the 
death  and  disintegration  of  a  certain  part ;  whilst  if  they  be  allowed  to 
remain  in  repose  for  a  time,  only  that  amount  of  decomposition  will  take 
place,  to  which  their  chemical  character  renders  them  liable.  Again, 
we  may  trace  the  connexion  between  the  vital  activity  of  a  part  and  the 
duration  of  its  life,  by  comparing  the  transitory  existence  of  the  leaves 
of  a  Plant,  which  are  its  active  organs  of  nutrition,  with  the  comparative 
permanence  of  its  woody  stem,  the  parts  of  which,  when  once  completely 
formed,  undergo  very  little  subsequent  change.  The  most  striking 
manifestation  of  this  connexion,  however,  is  afforded  by  that  condition, 
in  which,  without  any  appreciable  amount  of  vital  activity  or  change, 
an  organized  structure  may  remain  unaltered  for  centuries ;  not  only 
presenting  at  the  end  of  that  time  its  original  structure,  but  being  pre- 
pared to  go  through  its  regular  series  of  vital  operations,  as  if  these  had 
never  been  interrupted.  This  state  may  be  designated  as  Dormant 
Vitality.  It  difi'ers,  on  the  one  hand,  from  Life;  because  Life  is  a 
state  of  Activity.  On  the  other  hand,  it  differs  from  Death ;  because 
Death  implies  not  merely  a  suspension  of  activity,  but  a  total  loss  of 
vital  properties.  Now  in  the  state  of  Dormant  vitality,  the  vital  pro- 
perties are  retained ;  but  they  are  prevented  from  manifesting  them- 


k 


40  NATURE  AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

selves,  by  the  want  of  the  necessary  conditions.  When  these  conditions 
are  supplied,  the  state  of  vital  activity  is  resumed,  and  all  the  functions 
of  life  go  on  with  energy. 

44.  Of  this  Dormant  Vitality  it  may  be  well  to  adduce  some  exam- 
ples ;  which  may  assist  in  impressing  on  the  mind  of  the  student  the 
general  views  here  put  forth.  This  condition  is  manifested  in  the  most 
remarkable  manner  by  the  seeds  and  germs  of  plants ;  many  of  which 
are  adapted  to  remain,  for  an  unlimited  period,  in  a  state  of  perfect 
repose,  and  yet  to  vegetate  with  the  greatest  activity,  as  soon  as  ever 
they  meet  with  the  necessary  conditions.  Thus  the  sporules  of  the 
Fungi,  which  can  only  develope  themselves  in  decaying  organized  mat- 
ter, seem  universally  diffused  through  the  atmosphere,  and  ready  to 
vegetate  with  the  most  extraordinary  rapidity,  whenever  a  fitting  oppor- 
tunity presents  itself.  This  at  least  appears  to  be  the  only  feasible 
mode  of  explaining  their  appearance,  in  the  forms  of  Mould,  Mildew, 
&c.,  on  all  moist  decaying  substances ;  and  that  there  is  no  improbabi- 
lity in  the  supposition  itself,  is  shown  by  the  excessive  multiplication  of 
these  germs,  a  single  individual  producing  not  less  than  ten  millions  of 
them,  so  minute  as  when  collected  to  be  scarcely  visible  to  the  naked 
eye,  rather  resembling  thin  smoke,  and  so  light  as  to  be  wafted  by 
every  movement  of  the  atmosphere ;  so  that,  in  fact,  it  is  difficult  to 
imagine  any  place  from  which  they  can  be  excluded. — Moreover,  it  is 
certain  that  an  equally  tenacious  vitality  exists  in  the  seeds  of  higher 
plants.  Those  of  most  species  inhabiting  temperate  climates  are 
adapted  to  remain  dormant  during  the  winter ;  and  may  be  easily  pre- 
served, in  dry  air,  and  at  a  moderate  temperature,  for  many  years. 
Some  of  those  which  had  been  kept  in  the  Herbarium  of  Tournefort 
during  upwards  of  a  century,  were  found  to  have  preserved  their  ferti- 
lity. Cases  are  of  no  unfrequent  occurrence,  in  which  ground  that  has 
been  turned  up,  spontaneously  produces  plants  dissimilar  to  any  in 
their  neighbourhood.  There  is  no  doubt  that  in  some  of  these  cases,  the 
seed  is  conveyed  by  the  wind,  and  becomes  developed  in  spots  which 
afford  congenial  soil,  as  already  remarked  in  the  case  of  the  Fungi. 
Thus  it  is  commonly  observed  that  clover  makes  its  appearance  on  soils 
which  have  been  rendered  alkaline  by  lime,  by  strewed  wood-ashes,  or 
by  the  burning  of  weeds.  But  there  are  many  authentic  facts,  which 
can  only  be  explained  upon  the  supposition,  that  the  seeds  of  the  newly- 
appearing  plants  have  lain  for  a  long  period  imbedded  in  the  soil,  at 
such  a  distance  from  the  surface  as  to  prevent  the  access  of  air  and 
moisture ;  and  that,  retaining  their  vitality  under  these  circumstances, 
they  have  been  excited  to  germination  when  at  last  exposed  to  the  re- 
quisite conditions.  Thus  Professor  Lindley  states  as  a  fact,  that  he 
has  raised  three  raspberry-plants  from  seeds  taken  from  the  stomach  of  a 
man,  whose  skeleton  was  found  thirty  feet  below  the  surface  of  the 
earth,  at  the  bottom  of  a  barrow  which  was  opened  near  Dorchester  ;  as 
his  body  had  been  buried  with  some  coins  of  the  Emperor  Hadrian, 
there  could  be  no  doubt  that  the  seeds  were  1600  or  1700  years  old. 
Again,  there  are  undoubted  instances  of  the  germination  of  grains  of 
wheat,  which  were  enclosed  in  the  wrappers  of  Egyptian  mummies, 


OF   VITAL  ACTIONS  IN   GENERAL.  41 

perhaps  twice  that  number  of  years  ago ;  the  wheat  being  different  in 
some  of  its  characters  from  that  now  growing  in  the  country. 

45.  These  facts  make  it  evident  that  there  is  really  no  limit  to  the 
duration  of  this  condition ;  and  that  when  a  seed  has  been  thus  pre- 
served for  ten  years,  it  may  be  for  a  hundred,  a  thousand,  or  ten  thou- 
sand, provided  that  no  change  of  circumstances  either  exposes  it  to  de- 
cay, or  calls  its  vital  properties  into  activity.  Hence  in  cases  wEere 
seeds  have  been  buried  deep  in  the  earth,  not  by  human  agency,  but  by 
some  geological  change,  it  is  impossible  to  say  how  long  anteriorly  to 
the  creation  of  man  they  may  have  been  produced  and  buried ;  as  in  the 
following  very  curious  instance. — Some  well-diggers  in  a  town  on  the 
Penobscot  River,  in  the  State  of  Maine  (New  England),  about  forty 
miles  from  the  sea,  came  at  the  depth  of  about  twenty  feet  upon  a  stra- 
tum of  sand ;  this  strongly  excited  curiosity  and  interest,  from  the  cir- 
cumstance that  no  similar  sand  was  to  be  found  anywhere  in  the  neigh- 
bourhood, and  that  none  like  it  was  nearer  than  the  sea-beach.  As  it 
was  drawn  up  from  the  well,  it  was  placed  in  a  pile  by  itself;  an  unwil- 
lingness having  been  felt  to  mix  it  with  the  stones  and  gravel  which 
were  also  drawn  up.  But  when  the  work  was  about  to  be  finished,  and 
the  pile  of  stones  and  gravel  to  be  removed,  it  was  necessary  also  to 
remove  the  sand-heap.  This,  therefore,  was  scattered  about  the  spot 
on  which  it  had  been  formed,  and  Avas  for  some  time  scarcely  remem- 
bered. In  a  year  or  two,  however,  it  was  perceived  that  a  number  of 
small  trees  had  sprung  from  the  ground  over  which  the  heap  of  sand 
had  been  strewn.  These  trees  became  in  their  turn  objects  of  strong 
interest,  and  care  was  taken  that  no  injury  should  come  to  them.  At 
length  it  was  ascertained  that  they  were  Beach-Plum  trees  ;  and  they 
actually  bore  the  Beach-Plum,  which  had  never  before  been  seen, 
except  immediately  upon  the  sea-shore.  The  trees  had  therefore  sprung 
from  seeds,  which  were  in  the  stratum  of  sea-sand,  that  had  been  pierced 
by  the  well-diggers.  By  what  convulsion  they  had  been  thrown  there, 
or  how  long  they  had  quietly  slept  beneath  the  surface,  cannot  possibly 
be  determined  with  exactness ;  but  the  enormous  length  of  time  that 
must  have  elapsed  since  the  stratum  in  which  the  seeds  were  buried 
formed  part  of  the  sea-shore,  is  evident  from  the  accumulation  of  no 
less  than  twenty  feet  of  vegetable  mould  upon  it. 

46.  Numerous  instances  will  be  related  in  the  succeeding  Chapter,  of 
the  occurrence  of  a  similar  condition  in  fully-developed  Plants,  and  even 
in  Animals  of  high  organization.  In  some  of  these  it  is  a  regular  part 
of  the  history  of  their  lives,  coming  on  periodically  like  sleep  ;  whilst  in 
others  it  is  capable  of  being  induced  at  any  time,  by  a  withdrawal  of 
some  of  the  conditions  essential  to  vital  activity.  In  regard  to  all  of 
them,  however,  it  may  be  observed,  that  the  vitality  can  only  be  retained, 
when  the  organized  structure  itself  is  secluded  from  such  influences  as 
would  produce  its  decay.  Thus,  the  hard  dry  tissue  of  the  seed  is  but 
little  liable  to  decomposition ;  and  all  that  is  usually  required  for  the 
prevention  of  change  in  its  structure,  is  seclusion  from  the  free  access 
of  air  and  from  moisture,  and  a  steady  low  or  moderate  temperature. 
If  a  seed  be  exposed  to  air  and  moisture,  but  the  temperature  be  not 
high  enough  to  occasion  its  germination,  it  will  gradually  undergo  decay, 


42  NATURE   AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

and  will  consequently  lose  its  vitality.  The  animal  tissues  are  more 
liable,  as  already  mentioned,  to  spontaneous  decomposition;  and  the 
only  instances  in  which  they  can  retain  their  vitality  for  a  lengthened 
period,  without  any  nutritive  actions,  are  those  in  which  all  decomposi- 
tion is  prevented,  either  by  the  action  of  cold,  or  by  the  complete  depri- 
vation of  air  or  of  moisture, — as  when  Frogs,  Snakes,  &c.,  have  been 
preserved  for  years  in  an  ice-house,  or  Wheel-Animalcules  have  been 
dried  upon  a  slip  of  glass. 

47.  The  class  of  phenomena  last  brought  under  notice,  serves  to  ex- 
hibit in  a  very  remarkable  manner  the  dependence  of  all  Vital  Action 
upon  certain  other  conditions,  than  those  furnished  by  the  organized 
structure  alone.  Thus  a  seed  does  not  germinate  of  itself ;  it  requires 
the  influence  of  certain  external  agencies,  namely,  warmth,  air  and 
moisture ;  and  it  can  no  more  produce  a  plant  without  the  operation  of 
these,  than  warmth,  air,  and  moisture  could  produce  it  without  a  germ 
prepared  by  a  pre-existing  organism.  Now  when  we  come  to  study 
these  conditions,  we  find  that  they  may  be  arranged  under  two  catego- 
ries, the  material  and  the  dynamical.  Thus,  a  seed  cannot  germinate 
without  sufficient  water  to  bring  the  contents  of  its  cells  into  a  state  in 
which  their  chemico-vital  reactions  can  take  place ;  and  it  must  be  sur- 
rounded with  an  atmosphere  containing  oxygen,  since  without  the  pre- 
sence of  this  element  the  necessary  chemical  transformations  cannot  go 
on.  Thus  oxygen  and  water  are  the  material  conditions  required  by 
the  germinating  seed  ;  in  almost  every  other  case,  alimentary  matters 
are  required  in  addition ;  but  these  the  seed  possesses  within  itself. 
Even  if  supplied,  however,  with  an  unlimited  amount  of  water  and  oxy- 
gen, the  seed  cannot  germinate,  unless  it  be  acted  on  by  Heat ;  and 
this,  in  fact,  may  be  considered  with  great  probability,  as  supplying  the 
force^  of  which  not  merely  the  chemical  transformations,  but  the  growth 
and  development  of  the  tissues  of  the  Plant,  are  the  manifestation.  This 
view  will  be  more  fully  developed  hereafter  (Sect.  3). 

48.  This  dependence  of  Vital  actions  upon  certain  external  Agencies, 
as  well  as  upon  the  properties  of  the  organism  which  manifest  them,  is 
no  greater  than  the  dependence  of  any  of  the  phenomena  exhibited  by 
an  Inorganic  substance,  upon  some  other  agency  external  to  itself.  In 
fact,  no  change  whatever  can  he  said  to  he  truly  spontaneous;  that  is, 
no  property  can  manifest  itself,  unless  it  be  called  into  action  by  some 
stimulus  fitted  to  excite  it.  Thus,  when  spontaneous  decomposition  (as 
it  is  commonly  termed)  occurs  in  an  organized  or  an  inorganic  substance, 
it  is  due  to  the  forces  generated  by  the  mutual  attraction  between  cer- 
tain elements  of  the  substance,  and  the  oxygen  of  the  atmosphere  ;  and 
this  attraction  is  sufficient  to  overcome  that  which  tends  to  hold  toge- 
ther the  particles  in  their  original  state.  If  the  air  be  totally  excluded, 
decay  will  not  take  place  ;*  because  no  new  force  comes  into  operation, 
to  cause  a  separation  of  the  components  from  their  original  modes  of 
union.     The  influence  of  the  Dynamical  conditions  which  are  essential 

*  On  this  principle  meats,  vegetables,  and  even  liquid  soups,  are  now  largely  pre- 
served, for  the  use  of  persons  undertaking  long  voyages ;  by  enclosing  them  in  tin  cases, 
carefully  soldered  up.  There  is  no  limit  to  the  time,  during  which  decomposition  may 
thus  be  prevented. 


I 


OF   VITAL  ACTIONS   IN   GENERAL.  43 

to  Vital  activity,  will  be  fully  explained  in  the  next  Chapter ;  and  at 
present  it  will  be  sufficient  to  remark,  that  the  degree  in  which  they  are 
supplied  possesses  a  well-marked  influence  upon  the  amount  of  activity 
and  energy  manifested  in  the  actions  of  the  organized  structure ;  that 
there  is  a  limitation  in  the  case  of  each  of  them,  as  to  the  degree  in 
which  it  can  operate  beneficially,  the  limitation  being  usually  narrower 
and  more  precise,  according  to  the  elevation  of  the  being  in  the  scale ;~ 
that  an  excessive  supply  may  be  destructive  to  the  vital  properties  of 
the  organism,  by  over-stimulating  it,  and  thus  causing  it  to  live  too  fast, 
or  by  more  directly  producing  some  physical  or  chemical  change  in  its 
condition  ;  and  that  a  deficiency  will  keep  down  or  suspend  all  vital 
activity,  leaving  the  structure  to  the  unrestrained  operation  of  those 
agencies  which  are  always  tending  to  its  disintegration,  and  consequently 
occasioning  a  speedy  loss  of  the  vital  properties, — save  in  those  cases 
in  which  they  may  be  preserved  in  a  dormant  condition,  and  which  are 
exceptions  to  the  general  rule,  that  the  death  or  departure  of  the  vital 
properties  follows  closely  upon  the  cessation  of  vital  actions. 

49.  Our  fundamental  idea  of  Life,  then,  is  that  of  a  state  of  constant 
change  or  action ;  this  change  being  manifested  in  at  least  two  sets  of 
operations; — the  continual  withdrawal  of  certain  elements  from  the 
inorganic  world ; — and  the  incorporation  of  these  with  the  peculiar  struc- 
tures termed  organized,  or  the  production  from  them  of  the  germs  that 
are  hereafter  to  accomplish  this.  As  the  conditions  of  this  continual 
change,  we  recognise  the  necessity  of  an  organized  structure  on  the  one 
hand,  or  of  a  germ  which  is  capable  of  becoming  so ;  whilst  we  also  per- 
ceive the  necessity  of  a  supply  of  certain  kinds  of  matter  from  the  inor- 
ganic world,  capable  of  being  combined  into  the  materials  of  that  struc- 
ture, which  may  be  designated  as  the  alimentary  substances  ;  and,  fur- 
ther, we  see  that  the  organism  can  exert  no  influence  upon  these,  except 
with  the  assistance  of  certain  dynamical  agencies,  such  as  light,  heat, 
&c.,  that  supply  the  forces  ov  powers  without  which  no  change  can  occur. 
And  to  these  forces,  acting  under  the  conditions  which  the  Organized 
body  alone  can  supply,  may  be  attributed  (as  will  hereafter  appear)  the 
phenomena  which  we  distinguish  as  Vital. 

50.  But  just  as  we  find  among  Inorganic  bodies,  that  various  kinds 
are  to  be  distinguished  by  their  difierent  properties,  whilst  all  agree  in 
the  general  or  essential  properties  of  matter,  so  do  we  find  that  living 
organized  substances  are  distinguished  by  a  variety  of  properties  inherent 
in  themselves,  whilst  they  all  agree  in  the  foregoing  general  or  essential 
characters.  ^  In  many  instances,  the  difference  of  their  properties  is  as 
obviously  coincident  with  differences  in  their  structure  and  composition, 
as  it  usually  is  among  the  bodies  of  the  Mineral  world :  thus  we  find  the 
property  of  Contractility  on  the  application  of  a  stimulus,  to  be  for  the 
most  part  restricted  to  a  certain  form  of  organized  tissue,  the  Muscular; 
and  we  find  that  the  property  by  which  that  stimulus  is  capable  of  being 
generated  and  conveyed  to  a  distance,  seems  to  be  restricted  to  another 
kind  of  tissue,  the  Nervous.  In  a  great  number  of  cases,  however,  very 
obvious  diff'erences  in  properties  manifest  themselves,  when  no  perceptible 
variation^  exist,  either  in  structure  or  composition;  thus  it  would  be 
impossible  to  distinguish  the  germ-cell  of  a  Zoophyte  from  that  of  Man, 


44  NATURE   AND   OBJECTS   OF   PHYSIOLOGICAL  SCIENCE. 

by  any  difference  in  its  aspect  or  composition ;  yet  neither  can  be  deve- 
loped into  any  other  form  than  that  of  the  parent  species,  and  they  must 
be  regarded,  therefore,  as  essentially  different  in  properties.  In  the 
same  manner  we  shall  find  that,  in  the  same  organized  fabric,  there  are 
very  great  varieties  in  the  actions  of  its  component  cells,  which  indicate 
a  similar  variety  in  their  properties ;  and  yet  they  are  to  all  appearance 
identical.  But  there  can  be  no  reasonable  doubt,  that  differences  really 
exist  in  such  cases ;  though  our  means  of  observation  are  not  such  as 
to  enable  us  to  take  cognizance  of  these,  by  the  direct  impressions  they 
make  upon  our  senses.  Analogous  instances  are  not  wanting  in  the 
Mineral  world ;  for  the  Chemist  is  familiar  with  a  class  of  compounds 
designated  isomorphous,  in  which,  with  perfect  similarity  in  external 
form  and  physical  properties,  there  is  a  difference,  more  or  less  com- 
plete, in  chemical  composition,  and  consequently  in  the  effects  of  re- 
agents. 

51.  Whatever  may  be  the  peculiar  vital  properties  possessed  by  an 
organized  tissue,  we  find  that  they  are  always  dependent  upon  the  main- 
tenance of  its  characteristic  structure  and  composition,  by  the  nutritive 
operations  of  which  we  have  spoken ;  and  that  their  existence  forms  a 
part,  as  it  were,  of  the  more  general  phenomena  of  its  Life.  They 
manifest  themselves  with  the  first  complete  development  of  the  tissue ; 
they  are  retained  and  exhibited  so  long  as  active  nutritive  changes  are 
taking  place  in  it ;  their  manifestation  is  weakened  or  suspended  if  the 
nutritive  operations  be  feebly  exerted;  and  they  depart  altogether, 
whenever,  by  the  cessation  of  those  actions,  and  the  uncompensated 
influence  of  ordinary  Chemical  forces,  the  structure  begins  to  lose  that 
normal  composition  and  arrangement  of  parts,  which  constitutes  its  state 
of  organization.  Hence  we  may  regard  these  peculiar  properties  as  con- 
formable, in  all  the  essential  conditions  of  their  existence,  with  those 
more  general  properties,  which  have  been  previously  dwelt  upon  as 
characterizing  a  living  organized  structure. 

3.    Of  the  Forces  concerned  in  the  Production  of  Vital  Phenomena. 

52.  In  prosecuting  his  inquiry  into  the  causes  of  those  phenomena 
of  Living  organisms,  which,  being  of  a  totally  different  order  from  those 
of  Inorganic  matter,  are  distinguished  as  Vital,  the  Physiologist  must 
take  as  his  guide  those  methods  of  investigation,  which  have  proved 
successful  in  other  departments  of  scientific  research.  If  he  turn, 
then,  to  the  sciences  of  Mechanics,  Optics,  Thermotics,  Electricity, 
Magnetism,  or  Chemistry,  he  finds  that  the  phenomena  which  they 
respectively  comprise  are  referable  to  the  operation  of  certain  forces, 
and  that  what  are  termed  the  laws  of  those  sciences,  are  nothing  else 
than  expressions  of  the  conditions  of  action  of  those  forces.  Thus  in 
Mechanics  we  have  principally  to  do  with  the  motion  of  masses  of  mat- 
ter, and  our  idea  of  force  is  chiefly  derived  from  our  own  experience  of 
the  exertion  of  a  power  in  producing  or  resisting  motion ;  whilst  the 
'  laws'  of  Mechanics  are  nothing  else  than  expressions  of  the  conditions, 
under  which  the  forces  or  powers  that  produce  motion  opeijate  upon 
matter.     So  in  Optics,  we  have  to  do  with  the  force  which  we  term  light ; 


OF  VITAL  FORCE  IN  GENERAL.  45 

and  the  laws  of  Optics  are  expressions  of  the  conditions  under  which 
that  force  is  propagated,  and  of  its  action  on  material  substances.  In 
Thermotics,  again,  we  have  to  do  with  the  force  of  Heat ;  and  its  laws 
are  expressions  of  the  circumstances  under  which  heat  is  propagated, 
and  of  the  changes  which  it  occasions  in  the  substances  it  affects.  So  in 
the  sciences  of  Electricity  and  Magnetism^  we  have  to  do  with  the  forces 
known  under  those  names  ;  and  with  the  laws  expressive  of  their  action" 
upon  matter.  And  the  scientific  Chemist  refers  all  the  phenomena  with 
which  he  is  concerned  to  the  operations  of  Chemical  Affinity^  and  endea- 
vours to  deduce  from  observation  of  the  phenomena  the  laws  of  the 
operation  of  this  force. — So  the  Physiologist  will  be  justified  in  assuming 
a  Vital  Force  (or  Forces)  as  the  power  which  operates  in  producing 
Vital  phenomena  ;  and  will  most  legitimately  pursue  his  science,  in 
inquiring  into  the  conditions  under  which  that  force  operates. 

53.  The  analogy  of  the  Physical  Sciences  may  be  advantageously 
pursued  further. — Although  we  are  accustomed  to  speak  of  the  power 
that  produces  Mechanical  Motion,  of  Light,  of  Heat,  of  Electricity,  of 
Magnetism,  and  of  Chemical  Afiinity,  as  distinct  forces^  yet  it  has  gra- 
dually become  apparent  that  very  intimate  relations  subsist  between 
them,  and  that  they  are,  in  fact,  mutually  convertible  ;  so  that  one  force 
(a)  operating  upon  a  certain  form  of  matter,  ceases  to  manifest  itself, 
but  developes  another  force  (b),  in  its  stead ;  whilst,  in  its  turn,  the 
second  force  (b)  may  be  reconverted  into  the  first  (a),  or  into  some  other 
(c),  which,  again,  may  reproduce  either  the  first  (a),  or  second  (b),  or 
some  other  (d  or  e). — It  was  in  the  case  of  Electricity  and  Magnetism, 
that  this  reciprocal  relation,  which  is  designated  as  '  correlation,'  was 
first  clearly  apprehended.  If  an  electric  current  be  passed  round  a  piece 
of  soft  iron,  that  iron  becomes  magnetic,  and  remains  so  as  long  as  the 
current  is  circulating :  on  the  other  hand,  from  a  magnet  put  in  motion, 
an  electric  current  may  be  obtained.  Hence  we  are  accustomed  to  con- 
nect these  two  forces  under  the  term  Electro-Magnetism ;  but  they  can 
be  easily  shown  to  be  quite  distinct  in  their  modes  of  operation  on  matter ; 
and  their  relation  is  not  really  more  intimate  than  that  of  other  forces. 
For  Heat  may  be  developed  by  Electricity  ;  as  when  a  galvanic  current, 
sent  through  a  thin  platinum  wire,  heats  it  to  ignition,  or  even  fuses  it. 
Conversely,  Electricity  may  be  developed  by  Heat ;  as  when  heat  is 
applied  to  bars  composed  of  dissimilar  metals  in  contact  with  each  other. 
Again,  if  Mechanical  Motion  be  retarded,  as  in  friction,  we  immediately 
have  a  development  either  of  Heat  or  of  Electricity ;  heat  alone  being 
developed,  when  the  two  rubbing  surfaces  are  composed  of  precisely  the 
same  substance ;  and  electricity  being  produced,  when  these  substances 
are  different.  And  it  is  for  the  most  part  through  the  medium  of  Heat 
or  Electricity,  that  the  force  of  Mechanical  Motion  is  '  correlated'  to 
Light,  Magnetism,  and  Chemical  Affinity. 

54.  The  idea  of  correlation  also  involves  that  of  a  certain  definite  ratio, 
or  relation  of  equivalence,  between  the  two  forces  thus  mutually  inter- 
changeable ;  so  that  the  measure  of  force  B,  which  is  excited  by  a  certain 
exertion  of  force  A,  shall,  in  its  turn,  give  rise  to  the  same  measure  of 
force  A,  as  that  originally  in  operation.  Thus,  when  an  electric  current 
is  set  in  motion  by  galvanic  action,  we  have  a  conversion  of  chemical 


46  NATURE   AND   OBJECTS   OF  PHYSIOLOGICAL   SCIENCE. 

force  (which  has  manifested  itself  in  the  decomposition  of  the  water  and 
the  oxidation  of  the  zinc)  into  electrical ;  but  the  electrical  current  may, 
in  its  turn,  be  made  to  produce  chemical  decomposition  ;  and  the  amount 
of  this  kind  of  change  which  it  will  effect,  bears  a  precise  correspon- 
dence (cceteris  paribus)  with  the  amount  of  zinc  which  has  undergone 
oxidation  in  the  galvanic  cell.  In  like  manner,  when  water  at  212°  is 
converted  into  steam,  the  heat  which  it  receives  is  no  longer  manifested 
as  heat,  but  mechanical  force  is  developed  in  its  stead,  and  this  in  a 
certain  definite  ratio,  so  that  the  '  mechanical  equivalent'  of  heat  is  capa- 
ble of  being  exactly  determined :  so  soon,  however,  as  the  steam,  losing 
its  elasticity  by  condensation,  returns  to  the  condition  of  water,  the 
original  equivalent  of  heat  is  again  developed,  its  mechanical  force  being 
no  longer  manifested.* 

55.  Now  in  every  case  in  which  one  force  is  thus  converted  into 
another,  the  change  is  effected  through  the  medium  of  a  certain  form  of 
matter,  or  material  substratum.  This  may  be,  in  some  cases,  of  almost 
any  description  whatever ;  as  when  Heat  is  produced  by  the  friction  or 
retarded  motion  of  solids,  liquids,  or  even  gases ;  or  when  Motion  (as 
shown  in  expansion)  is  produced  by  the  application  of  heat  to  any  kind 
of  material  substance.  But  in  other  cases,  the  change  can  only  be 
effected  through  some  special  form  of  matter ;  or  if  several  substances 
may  serve  as  its  medium,  there  is  some  one  which  is  greatly  superior  to 
all  the  rest,  in  the  readiness  with  which  a  certain  force  manifests  itself 
through  it.  Thus  iron  is  the  only  substance  through  which  Electricity 
can  be  converted  into  Magnetism ;  and  the  development  of  magnetic 
force,  therefore,  can  only  take  place  through  this  medium.  So,  Heat 
is  more  readily  converted  into  Electricity  through  a  combination  of  bis- 
muth and  antimony,  than  through  any  other  metals ;  and  the  affection 
of  Light  by  magnetic  force  (discovered  a  few  years  since  by  Prof.  Fara- 
day), though  producible  through  any  transparent  substance,  can  be  made 
much  more  obvious  when  the  magnetism  is  made  to  act  upon  a  peculiar 
glass  composed  of  vitrified  borate  of  lead,  than  through  the  medium  of 
any  other  substance  yet  known.  This  speciality  in  the  action  of  diffe- 
rent substances,  when  subjected  to  the  same  forces,  is  a  fact  of  funda- 
mental importance ;  and  it  is  on  it,  indeed,  that  our  notion  of  their 
several  properties  depends. 

56.  Now  as  the  properties  of  every  kind  of  matter  require  certain 
conditions  for  their  manifestation,  our  acquaintance  with  them  entirely 
depends  upon  whether  the  conditions  of  their  action  have  been  afforded. 
Thus,  to  go  back  to  a  former  illustration,  supposing  a  new  chemical 

=*  The  above  statement  is  an  expression  of  the  simple  facts  of  the  case,  which,  when 
thus  understood,  render  the  hypothesis  of  "  latent  heat"  altogether  unnecessary.  This 
hypothesis,  however  ingenious,  will  doubtless  share  the  fate  of  many  other  such 
attempts  to  substitute  a  form  of  words  for  realities.  It  supposed  the  966  degrees  of 
heat  expended  in  converting  a  certain  amount  of  water  at  212°  into  steam  at  212°,  to 
become  altogether  inactive  or  latent ;  and  gave  no  account  whatever  of  the  mechanical 
force  which  is  produced  in  that  act  of  conversion.  The  idea  of  an  inactive  force,  in  fact, 
is  one  that  cannot  be  entertained ;  for  if  a  force  ceases  to  be  active,  it  is  no  longer 
<  force.'  And  it  cannot  be  imagined  that  force,  any  more  than  matter,  should  cease  to 
exist;  it  wwsi  manifest  itself  under  some  other  aspect. — For  a  complete  exposition  of 
the  mutual  relations  existing  among  the  above-named  agents,  see  Prof.  Grove's  treatise 
*'  On  the  Correlation  of  the  Physical  Forces." 


OP  VITAL  FORCE  IN  GENERAL.  47 

element  to  be  discovered,  we  could  not  know  its  properties  in  regard  to 
heat,  electricity,  or  magnetism,  the  mode  of  its  combination  with  other 
elements,  the  nature  and  properties  of  the  compounds  produced,  their 
reactions  with  other  compounds,  &c.,  until  we  have  tried  a  complete 
series  of  experiments  upon  it, — that  is,  until  we  have  placed  it  in  all  the 
circumstances  or  conditions  requisite  to  manifest  the  properties,  wiiJi_ 
which  we  seek  to  become  acquainted,  or  whose  absence  we  seek  to  de- 
termine if  they  do  not  exist.  Now  we  might  have  made  all  the  experi- 
ments we  could  devise  upon  such  a  body ;  and  yet  we  might  have  failed 
in  detecting  some  remarkable  and  distinguishing  property  inherent  in  it, 
simply  because  we  had  not  placed  it  in  the  requisite  circumstances  for 
the  manifestation  of  this  peculiarity.  Further,  even  in  the  elements  or 
compounds  with  which  we  are  best  acquainted,  it  is  very  possible  that 
properties  exist,  of  which  w^e  as  yet  know  nothing,  simply  because  they 
have  not  yet  been  called  into  action  by  the  requisite  combination  of 
conditions.  For  example,  no  one  would  have  thought  it  possible,  a  few 
years  since,  that  water  could  be  frozen  in  a  red-hot  metallic  vessel ;  and 
yet  this  is  now  known  to  be  effected  with  ease  and  certainty,  in  the 
proper  combination  of  conditions. 

57.  Again,  the  properties  of  a  compound  substance  are,  in  general  at 
least,  altogether  different  from  those  which  present  themselves  in  either 
of  its  components;  so  that  we  could  not  in  the  least  degree  judge  of  the 
former  from  the  latter,  or  of  the  latter  from  the  former.  What  more 
different,  for  example,  than  the  physical  and  chemical  properties  of 
Water,  from  those  of  either  the  Oxygen  or  the  Hydrogen  that  enter 
into  its  composition  ?  Or  what  more  different  than  the  properties  of  a 
neutral  salt,  from  those  of  the  acid  and  alkali  by  w^hose  union  it  is  pro- 
duced ? — Further,  the  properties  of  a  substance  may  be  completely 
changed,  by  an  alteration  in  its  condition  as  regards  Heat  or  any  other 
of  the  forces,  already  mentioned.  For  example,  the  particles  of  water 
have  so  strong  an  attraction  for  each  other,  at  a  low  temperature,  as  to 
become  aggregated  in  a  crystalline  form,  and  to  produce  a  dense  solid 
mass  ;  at  somewhat  a  higher  temperature,  their  mutual  attraction  is  so 
slight,  that  a  very  small  amount  of  mechanical  force  is  sufficient  to  sepa- 
rate them,  and  they  move  upon  each  other  with  the  utmost  freedom ; 
whilst  at  a  still  higher  temperature,  they  manifest  a  power  of  mutual 
repulsion,  which  increases  with  the  greatest  rapidity  with  every  augmen- 
tation of  temperature.  Yet  when  the  temperature  of  the  substance  is 
lowered  to  its  former  standards,  we  observe  that  it  first  returns  to  the 
liquid,  and  then  to  the  solid  form ;  and  that,  in  those  states,  it  manifests 
all  the  properties  which  before  characterized  it.  Not  merely  the  phy- 
sical, but  the  chemical  properties  of  bodies  may  be  affected  by  a  change 
in  their  mechanical  condition.  Thus,  it  is  well  known  that  oxygen  and 
iron,  at  ordinary  temperatures,  have  a  mutual  affinity,  which  is  only 
sufficient  to  produce  a  slow  combination  between  them ;  whilst  at  high 
temperatures,  that  affinity  is  such  as  to  cause  their  rapid  and  energetic 
union.  Now  if  iron,  in  a  state  of  very  minute  division,  such  as  it  pos- 
sesses when  set  free  from  the  state  of  oxide  by  means  of  hydrogen,  at  the 
lowest  possible  temperature,  be  brought  into  contact  with  oxygen  or  even 
with  atmospheric  air,  at  ordinary  temperatures,  it  immediately  becomes 


48  NATURE   AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

red-hot,  and  is  converted  into  an  oxide.  The  minuteness  of  the  division, 
predisposing  to  chemical  union,  appears  to  be  the  occasion  of  our  power 
of  causing  many  substances  to  combine,  when  one  or  both  are  in  the 
nascent  state  (that  is,  when  just  set  free  from  some  other  combination), 
which  could  not  be  made  to  unite  in  any  more  direct  manner ;  thus,  when 
a  quantity,  however  minute,  of  any  preparation  of  arsenic  is  dissolved 
in  fluid  in  which  hydrogen  is  being  generated,  the  hydrogen  will  detach 
the  metal  from  its  previous  combination,  and  will  pass  forth  in  union 
with  it,  as  arseniuretted  hydrogen,  a  compound  which  cannot  be  formed 
by  the  direct  union  of  the  elements.  In  like  manner,  in  that  mechanical 
mixture  of  three  finely-divided  substances,  which  we  call  gunpowder,  the 
rapidity  with  which  combustion  is  propagated  through  the  largest  col- 
lection of  it,  is  entirely  dependent  upon  the  minute  subdivision  of  its 
components,  and  the  very  close  approximation  of  their  particles.  Hence 
it  may  be  very  correctly  said,  that  the  true  chemical  properties  of  the 
substances  are  not  manifested,  except  when  they  are  in  a  state  of  very 
minute  division ;  and  that  these  are  in  fact  obscured,  by  the  aggregation 
of  the  particles  into  masses.  Thus,  then,  we  are  at  no  loss  to  discover 
examples,  in  the  Inorganic  world,  of  an  alteration  in  the  sensible  pro- 
perties, both  Chemical  and  Physical,  of  the  bodies  composing  it,  by  a 
change  in  the  conditions  in  which  they  are  placed.  And  it  may  be 
stated  as  a  general  fact,  that  we  never  witness  the  manifestation  of  new 
properties  in  a  substance,  unless  it  has  undergone  some  change  in  its 
own  condition,  of  which  altered  state  these  properties  are  the  necessary 
attendants. 

58.  Now  if  we  apply  the  same  methods  to  the  phenomena  of  Life,  we 
shall  see  that  they  will  lead  to  a  mode  of  viewing  them,  which  will  con- 
siderably tend  to  the  simplification  of  Physiological  science.  In  the 
first  place  we  have  to  look  at  these  phenomena  as  the  results  of  certain 
forces^  acting  through  those  forms  of  matter  which  we  term  Organized ; 
and  these  forces  we  shall  provisionally  designate  as  Vital.  Thus  in  the 
growth  of  the  simple  Vegetable  cell,  as  already  described  (§§  26-41), 
we  trace  the  operation  of  a  force  closely  allied  to  ordinary  chemical 
affinity^  but  so  far  difi*erent  that  it  can  only  be  exerted  through  a  living 
organism ;  of  a  force  of  assimilation  or  vital  transformation ;  and  of  a 
force  of  organization  and  complete  vitalization.  Now  although  we  may 
provisionally  designate  these  as  distinct  forces,  on  account  of  the  diver- 
sity of  their  manifestations,  it  is  impossible  not  to  see  that  they  are 
mutually  dependent,  and  that  they  form  the  successive  elements  of  a 
continuous  series  of  phenomena  belonging  to  the  same  category,  that  of 
cell-life;  and  further,  we  observe  that  they  operate  under  the  same 
conditions,  namely,  the  presence  of  a  cell-germ  and  of  the  materials  of 
its  growth,  and  the  action  of  light  and  heat.  Again,  in  the  multiplica- 
tion of  the  original  cell,  by  whatever  method  performed,  we  cannot  but 
trace  the  continued  action  of  forces  of  the  same  character ;  since  this 
operation  takes  place  as  a  continuation  of  the  process  of  growth,  and 
under  precisely  the  same  influences.  Further,  we  occasionally  meet 
with  examples,  even  among  the  simplest  forms  of  Vegetation,  of  very 
active  movement ;  thus  the  filaments  or  elongated  cells  of  the  OscillatO' 
rice  are  continually  bending  themselves  backwards  and  forwards,  with  a 


OF  VITAL  FORCE  IN   GENERAL.  49 

regular  rhythmical  undulation;  and  the  "zoospores"  of  the  Confervece 
are  propelled  through  the  water  by  the  rapid  vibration  of  the  cilia  with 
which  they  are  furnished  (§  234).  Now  that  such  a  production  of  a 
purely  physical  change  is  a  manifestation  of  vital  force,  is  obvious  from 
this, — that  it  takes  place  only  while  the  vitality  of  the  organism 
endures,  and  that  it  is  dependent  upon  the  very  same  conditions  as  the 
other  vital  operations  require ;  and  it  is  further  interesting  to  remark 
in  the  case  of  the  "zoospores,"  that  it  seems  to  take  the  place  of  the 
operations  of  growth,  for  these  do  not  commence  until  the  movement  of 
the  spore  has  ceased.  The  spiral  filaments,  again,  which  have  been 
discovered  in  most  of  the  higher  Cryptogamia,  and  which  seem  to  per- 
form the  same  function  with  the  spermatozoa  of  Animals  (§  240),  have 
a  similar  spontaneous  movement,  which  must  be  looked  upon  as  an  ex- 
pression of  their  vital  force.  Many  cases  of  motion  produced  by  a 
change  of  form  of  certain  contractile  cells,  might  be  cited  from  among 
the  higher  tribes  of  the  Vegetable  kingdom ;  these  movements  being 
sometimes  rhythmical  and  spontaneous,  as  in  the  Hedysarum  gyrans^ — 
sometimes  taking  place  only  in  respondence  to  stimulation,  as  in  the 
Dionoea  museipula  (Venus's  fly-trap), — and  sometimes  occurring  as  part 
of  the  series  of  ordinary  vital  phenomena,  although  producible  also  by 
stimulation,  as  in  the  Mimosa  pudiea  (sensitive  plant),  which  regularly 
closes  its  leaves  at  night,  but  will  do  so  at  any  time  when  they  are 
touched  or  otherwise  irritated.*  These  movements  only  take  place 
during  the  life  of  the  Plant ;  and  it  is  particularly  observable  in  the 
last-named  species,  that  the  facility  with  which  they  may  be  excited  in 
any  individual  is  closely  related  to  the  activity  of  its  vegetating  pro- 
cesses. Thus  even  in  the  Plant,  we  see  that  the  Vital  forces  manifest 
themselves,  not  merely  in  growth,  but  in  movement. 

59.  When  we  examine  the  structure  of  one  of  the  higher  Plants,  we 
find  that,  although  the  principal  part  of  its  fabric  is  still  made  up  of 
unmetamorphosed  cells,  yet  that  certain  portions  of  it  have  undergone 
histological  transformation;  that  is,  its  primordial  cells  have  lost  their 
original  character,  having  been  changed  into  other  kinds  of  tissue. 
This  transformation  takes  place  to  a  much  greater  extent  in  the  Animal 
body ;  in  which  the  variety  of  actions  to  be  performed  is  much  larger, 
and  in  which  we  accordingly  find  a  much  greater  variety  of  tissues  de- 
veloped as  their  instruments.  But  however  widely  these  tissues  may 
depart  from  their  original  character,  we  find  that  the  process  of  trans- 
formation takes  place  under  the  same  conditions  as  that  of  growth,  and 
must  be  regarded  as  a  continuation  of  it ;  being,  in  fact,  the  special 
manifestation  of  vital  force  in  one  set  of  cells,  as  multiplication  is  in 
another,  or  as  motion  in  another.  And  we  shall  find,  that,  in  proportion 
as  this  transformation  takes  place,  do  the  tissues  lose  their  proper  vital 
endowments ;  for  it  may  be  stated  as  a  general  fact,  that  even  in  the  most 
complicated  and  elaborate  Animal  organism,  all  the  most  active  vital  ope- 
rations are  performed  by  tissues  which  retain  their  original  cellular  con- 
stitution with  little  or  no  change. — Further,  it  is  to  be  observed,  that  as  it 
is  the  peculiar  character  of  such  organisms  that  each  of  their  parts  should 

*  For  a  fuller  analysis  of  these  phenomena,  see  the  Author's  "Principles  of  Physio- 
logy, General  and  Comparative,"  chap.  xix. 

4 


56  NATURE  AND   OBJECTS   OF   PHYSIOLOGICAL   SCIENCE. 

be  appropriated  to  some  distinct  office  which  it  is  specially  adapted  to  per- 
form, so  do  we  find  that  the  cells  which  become  the  instruments  of  some 
one  particular  kind  of  operation  seem  to  lose  their  other  endowments ; 
as  if  the  expenditure  of  the  vital  force  of  each  cell  upon  any  one  pur- 
pose, unfitted  it  for  any  other  agency.  Of  this  we  shall  meet  with 
numerous  examples  hereafter ;  it  will  be  sufficient  here  to  refer  to  two 
of  the  most  characteristic.  It  is  necessary  for  every  act  of  Secretion, 
that  a  set  of  cells  should  be  formed  within  the  ultimate  follicles  of  the 
Gland  which  is  the  instrument  of  the  function  (§  238);  and  these  ulti- 
mate follicles  are  really  to  be  regarded  as  parent-cells,  which  produce 
the  true  secreting  cells  in  proportion  as  the  materials  of  their  growth 
are  supplied  by  the  blood.  Now  these  parent-cells  themselves  possess 
no  secreting  power,  their  vital  forces  being  entirely  expended  in  the 
production  of  the  true  secreting  cells.  On  the  other  hand,  the  true 
secreting  cells  possess  no  reproductive  power,  but  die  and  are  cast  off 
when  they  have  reached  their  maturity ;  as  if  their  whole  vital  force 
were  expended  in  the  secreting  process,  which  is  nothing  else  on  their 
parts  than  an  act  of  growth.  So,  again,  the  cells  which  constitute  the 
fibrillse  of  Muscular  fibre,  and  of  whose  change  of  form  the  contraction 
of  the  muscle  is  the  result  (§  336),  exercise  no  power  of  chemical  transfor- 
mation, undergo  no  histological  change,  and  appear  to  be  entirely  desti- 
tute of  the  power  of  self-multiplication ;  the  expenditure  of  their  vital 
force  in  the  act  of  muscular  contraction  involves  their  death  and  disinte- 
gration ;  and  their  renewal  appears  to  be  accomplished  by  a  production  of 
new  cells  from  the  nucleus  of  the  Myolemma  (§  338),  which,  itself  pos- 
sessing no  contractile  power,  retains  its  reproductive  capacity. 

60.  Hence,  then,  we  have  reason  to  believe,  that  all  the  truly  Vital 
phenomena,  however  diversified,  are  but  results  of  the  operation  of  one 
and  the  same  Force,  whose  particular  manifestations  are  determined  by 
the  nature  of  the  material  substratum  through  which  it  acts :  the  same 
fundamental  agency  producing  simple  growth  in  one  case,  transformation 
in  another,  multiplication  in  a  third,  mechanical  movement  in  a  fourth, 
whilst  in  a  fifth  it  developes  nervous  power,  which  may  itself  operate 
in  a  variety  of  different  modes.  Such  a  view  seems  fully  justified  by 
the  consideration,  (1)  that  all  these  forces  are  exerted,  even  in  the 
most  highly-organized  living  being,  through  a  common  instrumentality, 
the  simple  cell ;  (2)  that  the  entire  assemblage  of  cells  making  up  the 
totality  of  any  organism,  have  all  a  common  parentage,  being  lineally 
descended  from  the  single  primordial  cell  in  which  it  originated ;  and 
(3)  that  they  are  manifested  in  connexion  with  each  other,  as  parts  of 
the  life  of  each  individual  cell,  in  those  simple  organisms  which  are  the 
lowest  members  of  the  two  kingdoms  respectively,  and  in  which  there 
is  no  separation  or  specialization  of  function. 

61.  The  question  next  arises, — what  is  the  source  of  the  Vital  Force, 
of  which  the  phenomena  of  Life  are  the  manifestations ;  and  under  the 
guidance  of  the  ideas  derived  from  Physical  Science,  we  shall  have  no 
difficulty  in  referring  it  to  the  operation  of  those  external  agencies,  the 
influence  of  which  has  long  been  known  to  be  essential  to  Vital  action, 
and  which  have  been  usually  designated  by  the  term  Vital  Stimuli. 
Thus,  the  growing  Vegetable  cell  cannot   decompose   carbonic   acid, 


OF  VITAL  FORCE  IN  GENERAL.  51 

except  when  acted  upon  bj  Light ;  and  the  amount  of  this  change 
which  it  effects,  is  in  strict  ratio  (eceteris  paribus),  with  the  illuminating 
power  of  the  rays  which  it  receives  (§  86).  So,  again,  neither  Plants 
nor  Animals  can  maintain  their  activity,  except  under  the  continual 
influence  of  a  certain  measure  of  Heat ;  and  the  amount  of  that  activity 
will  be  shown  to  bear  a  constant  ratio,  in  all  those  tribes  which  have 
no  independent  power  of  sustaining  it,  to  the  quantity  which  they  receive 
from  external  sources  (chap.  ii.  Sect.  2) ;  this  being  true,  not  merely 
of  the  general  rate  of  the  Vegetative  actions  of  growth  and  development, 
but  also  of  those  manifestations  of  vital  power  which  are  peculiar  to 
Animals.  Thus  we  may  say,  that  Light  and  Heat  acting  upon  the 
organic  germ,  become  transformed  into  Vital  force,  in  the  same  manner 
as  Heat  acting  upon  a  certain  combination  of  metals  becomes  Electricity, 
or  as  Electricity  acting  upon  iron  developes  itself  as  Magnetism ;  and 
we  shall  find  that  this  view  is  in  complete  harmony  with  all  the  pheno- 
mena of  Vital  action.  Moreover,  the  Vital  force  thus  engendered  fre- 
quently manifests  itself  in  producing  Physical  or  Chemical  phenomena ; 
thus  completing  that  mutual  relationship,  or  correlation,  which  has  been 
shown  to  exist  among  the  Physical  and  Chemical  forces  themselves  (§§  53, 
54).  Of  this  we  have  already  seen  an  instance  in  the  movements  pro- 
duced by  muscular  contraction  and  by  ciliary  vibration.  The  production 
of  heat  by  certain  Plants  and  by  warm-blooded  Animals,  is  another  appo- 
site exemplification  of  the  same  principle.  But  the  most  remarkable 
illustration  is  undoubtedly  derived  from  the  Nerve-force ;  which,  whilst 
itself  a  peculiar  form  of  the  general  Vital  force,  and  capable  of  affecting 
all  the  other  manifestations  of  the  same  force  (as  in  the  modifications 
which  it  produces  in  the  processes  of  Nutrition  and  Secretion,  as  well  as 
in  exciting  Muscular  Contraction),  is  capable  of  developing  Electricity  as 
well  as  Light  and  Heat,  and  is  also  capable  of  being  called  forth  by  the 
action  of  Light,  Heat,  Electricity,  Chemical  Afiinity,  or  even  Mechan- 
ical Motion,  on  the  Nervous  tissue.  It  is  a  most  remarkable  confirma- 
tion of  the  views  here  advanced,  that  the  nerve-force,  which  must  be 
accounted,  in  its  relations  to  Mind,  as  the  highest  of  all  the  forms  of 
Vital  force,  should  yet  be  the  one  which  is  most  directly  and  intimately 
related  to  the  Physical  forces, — the  '^  correlation"  even  of  Electricity 
and  Magnetism  not  being  more  complete,  than  the  "correlation"  of 
Electricity  and  Nerve-force  may  be  shown  to  be  (§  396). 

62.  Thus,  then,  not  only  are  the  materials  drawn  from  the  Inorganic 
world  by  vital  agencies,  given  back  to  it  again  by  the  disintegration  of 
the  living  structures  of  which  they  form  a  part ;  but  all  the  forces  which 
are  operative  in  producing  the  phenomena  of  Life,  being  first  derived 
from  the  Inorganic  universe,  are  returned  to  it  again  under  some  form 
or  other.  ^  The  Plant  forms  those  organic  compounds,  at  the  expense  of 
which  Animal  life  (as  well  as  its  own),  is  sustained,  by  the  decomposi- 
tion of  carbonic  acid,  water,  and  ammonia ;  and  the  light,  by  whose 
agency  alone  this  process  can  be  effected,  may  be  considered  as  meta- 
morphosed into  the  peculiar  affinity,  by  which  the  elements  of  these 
compounds  are  held  together.  The  heat  vfluch.  Plants  receive,  acting 
through  their  organized  structures  as  Vital  force,  serves  to  augment 
these  structures  to  an  almost  unlimited  extent,  and  thus  to  supply  new 


62  NATURE  AND  OBJECTS  OF   PHYSIOLOGICAL   SCIENCE. 

instruments  for  the  agency  of  light  and  for  the  production  of  organic 
compounds.  The  whole  nisus  of  Vegetable  life  may  be  considered  as 
manifested  in  this  production ;  and,  in  effecting  it,  each  organism  is  not 
only  drawing  material,  but  force,  from  the  universe  around  it.  Sup- 
posing that  no  Animals  existed  to  consume  these  organic  compounds, 
they  would  be  all  at  last  restored  to  the  inorganic  condition  by  sponta- 
aeous  decay,  which  would  reproduce  the  carbonic  acid,  water,  and  am- 
monia, from  which  they  were  generated.  In  this  decay,  however  slow, 
heat  and  light  are  given  out,  in  the  same  amount  as  when  more  evidently 
produced  in  the  ordinary  combustive  process  ;  and  this  sometimes  occurs 
even  during  the  life  of  the  plant,  whose  vital  movements,  also,  may  be 
considered  as  restoring  to  the  Inorganic  universe  a  certain  measure  of 
the  force  they  have  derived  from  it  under  other  forms.  Thus  in  making 
use  of  the  stores  of  Coal  which  have  been  prepared  for  his  wants  by  the 
luxuriant  Flora  of  past  ages,  Man  is  not  only  restoring  to  the  atmo- 
sphere the  carbonic  acid,  the  water,  and  the  ammonia,  of  the  Carboni- 
ferous period,  but  is  actually  reproducing  and  applying  to  his  own 
purposes,  the  Light  and  Heat  which  were  operating  to  produce  the 
growth  of  vegetation  at  that  remote  period  in  the  Earth's  history. 

63.  But  the  organic  compounds  which  the  agency  of  Light  and  Heat 
upon  the  Vegetable  structures  has  produced,  are  designed  for  a  much 
higher  purpose,  than  that  of  being  merely  given  back  to  the  Inorganic 
universe  by  decay  or  combustion ;  and  the  forces  which  hold  together 
their  elements  have  a  much  more  exalted  destiny.  In  serving  as  the 
food  of  Animals,  a  part  of  them  become  the  materials  of  their  organized 
tissues,  and  the  instruments  through  which  the  nervous  and  muscular 
forces  are  developed;  whilst  another  part  are  applied  to  sustain  the 
combustive  process,  by  which  the  heat  of  the  higher  classes  is  main- 
tained quite  independently  of  the  external  supply  of  that  force.  The 
greater  part  of  the  Animal  kingdom,  however,  is  dependent,  like  the 
Vegetable,  upon  the  Inorganic  Universe,  for  the  Heat  which  serves  as 
its  organizing  force ;  and  it  is  only  under  the  constant  influence  of  this 
agent,  that  the  operations  of  growth,  development,  and  maintenance 
can  take  place.  The  Animal  is  not  dependent  like  the  Plant  upon  Light ; 
and  this  is  obviously  because  that  agent  is  chiefly  concerned  in  that 
preliminary  operation,  by  which  the  organic  compounds  are  generated 
as  the  pabulum  of  the  growing  tissues  ;  in  fact,  the  embryo  within  the 
germinating  seed,  which,  like  the  animal,  is  nourished  upon  matter 
previously  prepared  for  it,  is  most  rapidly  developed  in  the  absence  of 
light,  up  to  the  time  when,  its  store  being  exhausted,  its  further  sup- 
plies must  be  obtained  by  its  own  instrumentality. — The  Vital  activity 
of  Animals,  then,  may  be  considered  as  chiefly  sustained  by  the  Che- 
mical forces  subsisting  in  their  food,  which  are  set  free  when  the  ele- 
ments are  reconverted  to  their  original  state ;  and  by  the  Heat  which 
they  derive  from  external  sources,  or  from  the  combustion  of  a  part  of 
their  food.  These  forces  may  be  considered  as  in  a  state  of  continual 
restoration  to  the  Inorganic  Universe,  during  the  whole  life  of  Animals, 
in  the  heat,  light,  electricity,  still  more  in  the  motion,  which  they  deve- 
lope ;  and,  after  their  death,  in  the  production  of  heat  and  light  during 
the  processes  of  decay.     During  Animal  life,  there  is  a  continual  resto- 


OF  DEGENERATION  AND   DEATH.  53 

ration  to  the  mineral  world,  of  the  carbonic  acid,  water,  and  ammonia, 
which  have  been  appropriated  by  Plants ;  and  it  will  hereafter  appear, 
that  the  amount  thus  given  off  by  the  animal  organism  bears  a  close 
correspondence,  on  the  one  hand,  with  its  degree  of  vital  activity,  as 
shown  in  the  amount  of  heat  and  motion  which  it  generates,  and,  on  the 
other,  with  the  amount  of  the  organic  compounds  which  it  consumes  as 
food.  So  that,  on  the  whole,  there  is  strong  reason  to  believe  that  tEe 
entire  amount  of  force  (as  of  materials),  received  by  an  animal  during 
a  given  period,  is  given  back  by  it  during  that  period,  provided  that  its 
condition  at  the  end  of  the  term  is  the  same  as  it  was  at  first ;  and  fur- 
ther, that  all  the  force  (like  the  material),  which  has  been  expended  in 
the  building  up  of  the  organism,  is  given  back  by  its  decay  after  death.* 

4.    Of  Degeneration  and  Death. 

64.  We  have  seen  that  the  general  history  of  the  phenomena  of  Life 
is  fully  conformable  with  the  view,  that  the  Vital  properties  of  a  tissue 
(that  is,  the  properties  in  virtue  of  which  the  forces  that  act  upon  it 
are  caused  to  manifest  themselves  in  Vital  action),  are  dependent  upon 
that  state  of  combination  and  arrangement,  which  is  termed  Organiza- 
tion. As  long  as  each  tissue  retains  its  normal  or  regular  constitution, 
renovated  by  the  actions  of  absorption  and  deposition  through  which 
that  constitution  is  preserved,  and  surrounded  by  those  other  conditions 
which  a  living  system  alone  can  afford,  so  long,  we  have  reason  to  be- 
lieve, it  will  retain  its  vital  properties, — and  no  longer.  And  just  as 
we  have  no  evidence  of  the  existence  of  vital  properties  in  any  other 
form  of  matter  than  that  which  we  call  organized,  so  have  we  no  reason 
to  believe  that  organized  matter  can  retain  its  regular  constitution,  and 
be  subjected  to  the  appropriate  forces,  without  exhibiting  vital  actions. 
The  advance  of  pathological  science  renders  it  every  day  more  probable 
(indeed  the  probability  may  now  be  said  to  amount  to  almost  positive 
certainty),  that  derangement  in  function^ — in  other  words,  an  imperfect 
or  irregular  action^ — always  results,  either  from  some  change  of  struc- 
ture or  composition  in  the  tissue  itself,  or  from  some  corresponding 
change  in  the  forces  by  which  the  properties  of  the  organ  are  called 
into  action.  Thus,  when  a  Muscle  has  been  long  disused,  in  can  scarcely 
be  excited  to  contraction  by  the  usual  stimulus,  or  may  even  be  altoge- 
ther powerless  ;  and  minute  examination  of  its  structure  shows  it  to  have 
undergone  a  change,  which  is  obvious  to  the  microscope,  though  it  may 
not  be  perceptible  to  the  unaided  eye,  and  which  results  from  imperfect 
nutrition.  Or,  again,  convulsive  or  irregular  actions  of  the  Nervous 
system  may  be  produced,  not  by  any  change  in  its  own  composition, 
but  by  the  presence  of  various  stimulating  substances  in  the  blood, 
although  their  amount  be  so  small  that  they  can  scarcely  be  recognised. 
^  Q^,  As  there  is  a  constant  tendency,  in  the  Animal  tissues  more  espe- 
cially, to  spontaneous  decay,  so  must  the  maintenance  of  the  vital  pro- 

*  The  whole  of  this  subject  is  more  fully  developed  in  the  Author's  "Principles  of 
Physiology,  General  and  Comparative,"  chaps,  iii.  and  v. ;  and  in  a  Paper  on  "■  The 
Mutual  Relations  of  the  Vital  and  Physical  Forces,"  contained  in  the  Philosophical 
Transactions  for  1850. 


64  NATURE   AND   OBJECTS   OP   PHYSIOLOGICAL   SCIENCE. 

perties  depend  upon  their  continual  regeneration  by  the  nutritive  opera- 
tions. Hence  we  have  no  difficulty  in  accounting  for  the  Death  of  the 
whole  system,  on  the  cessation  or  serious  disturbance  of  any  one  impor- 
tant function ;  for  any  such  check  or  change  must  suspend  or  disorder 
the  nutrient  processes,  in  such  a  degree  that  they  can  no  longer  main- 
tain the  normal  constitution  of  the  several  tissues.  But  as  there  is  a  great 
variety  in  the  rapidity  of  the  decomposition  of  the  tissues,  when  the 
act  of  nutrition  is  suspended,  so  do  we  witness  a  corresponding  variety 
in  the  duration  of  their  vital  properties,  after  that  permanent  severance 
of  the  chain  of  functions,  which  is  distinguished  as  somatic  death, — i.  e., 
the  death  of  the  hodt/  as  a  whole.  It  is  by  the  Circulation  of  the  Blood, 
that  the  connexion  of  the  diiferent  functions  is  essentially  maintained ; 
that  fluid  being  not  only  the  material  for  the  nutrition  of  the  tissues,  but 
in  many  cases  supplying  also  the  stimulus  to  their  activity.  Hence 
with  the  permanent  cessation  of  the  Circulation,  somatic  death  must  be 
regarded  as  taking  place. 

6Q.  Yet  after  this,  we  observe  that  vitality  lingers  in  the  tissues ;  and 
that  it  departs  from  them  only  as  they  lose  their  proper  composition. 
Thus  we  find  that,  although  the  Nervous  centres  cannot  originate  the 
stimulus  necessary  to  produce  Muscular  contraction,  after  the  Circula- 
tion has  ceased, — yet  the  Nervous  fibres  can  convey  such  a  stimulus,  long 
after  somatic  death ;  so  that  contractions  may  be  excited  in  muscles  by 
the  application  of  galvanism,  or  of  mechanical  or  chemical  stimulants, 
to  the  trunks  that  supply  them.  The  molecular  death  of  the  Nervous 
tissue,  therefore,  has  not  yet  taken  place.  After  a  time,  however,  this 
power  is  lost ;  the  tissue  no  longer  exhibits  its  distinguishing  vital  pro- 
perties ;  and  incipient  decomposition  and  change  of  structure  manifest 
themselves.  Yet  for  some  time  after  this,  the  Muscular  tissue,  especially 
in  a  cold-blooded  animal,  continues  to  possess  its  peculiar  contractility ; 
for  contractions  may  be  excited  in  it,  by  stimuli  directly  applied  to  itself, 
long  after  the  nerves  have  ceased  to  convey  their  influence.  Sometimes, 
indeed,  the  contractility  of  muscle  endures,  until  changes  in  its  struc- 
ture and  composition  become  evident  to  the  senses ;  thus  the  heart  of  a 
Sturgeon,  removed  from  the  body,  and  hung  up  to  dry,  has  been  known 
to  continue  alternately  contracting  and  dilating,  until  the  movement  pro- 
duced a  crackling  noise,  in  consequence  of  the  dryness  of  the  texture. 
Again,  there  is  evidence,  that  various  processes  of  nutrition  and  secre- 
tion may  go  on,  for  some  time  after  somatic  death,  and  even  after  the 
removal  of  the  organs  from  the  body,  provided  a  sufficient  quantity  of 
blood  remains  in  them ;  and  the  blood  itself  retains  its  vitality,  so  as 
not  to  coagulate,  whilst  contained  in  the  vessels  of  tissues  still  living. 

67.  Hence  it  is,  that  parts  which  have  been  completely  separated  from 
the  body  may  often  be  reunited  with  it,  if  they  were  previously  in  a 
healthy  state,  and  too  much  time  have  not  elapsed ;  thus,  there  are  many 
cases  on  record,  in  which  fingers,  toes,  noses,  or  ears,  that  have  been 
accidentally  chopped  ofi^,  have  been  made  to  adhere  and  grow  as  before, 
by  bringing  the  cut  surfaces  into  contact,  even  some  hours  after  their 
severance.  It  is  evident,  then,  that  the  parts  so  severed  cannot  have 
lost  their  vitality ; ,  since  no  treatment  could  produce  union  between 
a  dead  mass  and  a  living  body.     And  we  are  fully  justified  in  assuming, 


OF  DEGENERATION  AND   DEATH.  55 

that,  in  cases  where  attempts  at  such  reunion  have  not  been  successful, 
the  death  of  the  separated  part  has  resulted  from  the  too  prolonged 
interruption  of  its  regular  nutritive  operations,  whereby  chemical  and 
physical  changes  have  taken  place  in  it,  and  destroyed  the  peculiar  struc- 
ture and  composition  of  its  several  parts.  The  ordinary  phenomena  of 
Death,  therefore,  as  well  as  those  of  Life,  bear  out  the  views  which  have 
been  here  advanced. 

68.  But  it  has  been  maintained  by  those  who  consider  Vitality  as 
something  superadded  to  an  Organized  Structure,  essentially  indepen- 
dent of  it,  and  capable  of  being  subtracted  from  it,  that  Death  frequently 
takes  place  under  circumstances,  which  leave  the  organism  as  it  was ;  so 
that  "  the  dead  body  may  have  all  the  organization  it  ever  had  whilst 
alive."  For  such  an  assumption,  there  is  not  the  least  foundation.  In 
nearly  all  cases  in  which  death  takes  place  as  a  result  of  disease,  the 
connexion  between  changes  of  structure  and  composition,  either  in  the 
tissues  or  in  the  blood,  and  such  a  loss  of  the  vital  properties  of  some 
part  or  organ  as  is  sufficient  to  bring  the  Circulation  to  a  stand,  is  so 
palpable  as  to  require  no  proof;  and  in  by  far  the  greater  majority  of 
cases  in  which  it  is  not  at  once  obvious,  a  more  careful  scrutiny  will 
reveal  it.  It  must  be  confessed  on  both  sides,  that  our  means  of  inves- 
tigation, and  our  knowledge  of  the  normal  structure  and  composition  of 
the  tissues  and  the  blood,  are  not  yet  sufficient  to  enable  us  to  detect 
minute  shades  of  alteration,  nor  to  assert  what  extent  of  change  is  incon- 
sistent with  the  continuance  of  life.  But  as  no  one  has  yet  shown,  by  the 
careful  and  exact  microscopical  and  chemical  examination  of  the  solids 
and  fluids  of  a  dead  body,  that  it  has  all  the  organization  it  had  whilst 
alive,  the  assertion  above  quoted  is  totally  unwarranted  by  experience, 
and  is  contradicted  by  all  our  positive  knowledge  of  the  matter. 
(See§187.)_ 

69.  But  it  has  been  urged,  that  Death  may  result  from  the  sudden 
operation  of  some  agency  of  an  immaterial  character,  which  leaves  no 
trace  behind  it, — such  as  a  powerful  electric  shock,  or  a  violent  mental 
emotion.  Here,  too,  the  argument  entirely  fails.  It  is  impossible  that 
a  powerful  electric  shock  could  be  transmitted  through  a  mass  like  the 
animal  body,  composed  of  elements  in  such  a  loose  state  of  combination 
that  they  are  always  undergoing  decomposition,  without  producing  impor- 
tant chemical  changes  in  it ;  and  its  imperfect  conducting  power  renders- 
it  equally  liable  to  physical  disturbances.  As  a  matter  of  fact  it  has 
been  noticed,  that  the  bodies  of  animals  killed  by  electricity  pass  into 
decomposition  with  unusual  rapidity ;  showing  that  the  ordinary  chemical 
affinities  of  their  components  have  received  a  powerful  stimulus ;  and  it 
has  also  been  ascertained,  that  when  eggs  in  process  of  development 
have  had  their  vitality  destroyed  by  an  Electric  shock,  the  minute  vessels 
of  the  vascular  area  (§  551)  have  been  ruptured. — ^Nor  is  it  more  difficult 
to  explain  the  immediate  cause  of  death,  as  a  result  of  Mental  emotion. 
In  some  cases,  an  obvious  physical  change  has  been  produced,  by  the 
too  violent  action  of  the  heart,  the  movements  of  which  are  stimulated 
by  the  emotion  ;  thus,  even  in  a  healthy  person,  rupture  of  the  heart  or 
aorta  has  been  known  to  take  place, — an  occurrence  to  which  those 
affected  by  previous  disease  of  that  organ  are  much  more  liable.    Where 


56  NATURE  AND   OBJECTS   OP  PHYSIOLOGICAL   SCIENCE. 

there  is  any  disorder  in  the  heart's  action,  resulting  from  thickened 
valves,  narrowed  orifices,  &c.,  the  physical  influence  of  mental  emotion 
can  be  easily  accounted  for.  But  it  must  be  admitted  that  cases  have 
occurred^  in  which  no  such  explanation  can  be  offered ;  sudden  death 
having  taken  place  without  any  perceptible  structural  cause.  We  are 
not  obliged,  however,  to  have  recourse  to  any  hypothesis,  for  an  explana- 
tion of  even  these  cases,  which  is  not  borne  out  by  ample  analogy.  For 
it  is  well  known  that  mental  emotions,  acting  through  the  nervous  force, 
exert  a  powerful  influence  over  the  composition  of  the  fluids  of  the  body, 
and  are  capable  of  instantaneously  altering  these.  Thus  in  many  human 
beings,  and  still  more  in  the  lower  animals,  alarm  or  agitation  will 
occasion  the  immediate  disengagement  of  powerfully  odorous  secretions, 
which  must  have  resulted  from  new  combinations  suddenly  formed ;  and 
a  fit  of  passion  may  immediately  occasion  such  a  change  in  the  milk  of 
a  nurse,  as  renders  it  a  rank  poison  to  the  infant.  There  is  no  reason 
to  doubt,  therefore,  that  the  blood  itself  may  undergo  changes  of  analo- 
gous character  from  the  same  cause ;  and  that  it  may  become  a  violent 
poison  to  the  individual  himself,  instead  of  being  the  source  of  whole- 
some nutriment,  or  the  stimulus  to  vital  activity. — But  the  effect  of 
Electricity,  of  mental  Emotion,  or  even  of  Mechanical  force,  may  be 
exerted  more  dynamically  than  organically ;  destroying  the  vital  powers, 
by  antagonizing  the  forces  that  produce  them,  without  occasioning  any 
perceptible  material  change.  This,  in  fact,  we  see  in  the  state  of  pros- 
tration or  '  shock,'  induced  by  sudden  and  violent  impressions  of  almost 
any  description. 

5.   General  Summary. 

70.  To  conclude,  then ; — we  only  know  of  Life,  as  exhibited  by  an 
Organized  structure,  when  subjected  to  the  operation  of  certain  forces 
which  call  it  into  activity ;  and  we  only  know  of  Vitality,  or  the  state 
or  endowment  of  the  being  which  exhibits  that  action,  as  conjoined  with 
that  particular  aggregation  and  composition  which  we  term  Organiza- 
tion. We  have  seen  that  the  act  of  Organization,  and  the  consequent 
development  of  peculiar  properties  in  the  tissues  which  are  produced  by 
it,  can  only  be  attributed  to  the  vital  force  of  a  pre-existing  organism ; 
and  hence  it  is,  that  whilst  the  operation  of  Physical  forces  upon  an 
organized  body  gives  rise  to  vital  phenomena,  no  such  phenomena  can 
be  manifested  as  the  result  of  their  action  upon  any  kind  of  inorganic 
matter.  It  is  in  fact,  the  speciality  of  the  material  instrument  thus  fur- 
nishing the  medium  of  the  change  in  their  modus  operandi,  which  es- 
tablishes, and  must  ever  maintain,  a  well-marked  boundary-line  between 
the  Physical  and  the  Vital  forces.  According  to  the  views  here  pro- 
pounded, the  Vital  force  is  as  different  from  Heat  or  Electricity,  as  they 
are  from  each  other ;  but  just  as  Heat,  acting  under  certain  peculiar 
conditions,  is  capable  of  transformation  into  Electricity,  whilst  Electri- 
city is  capable,  under  certain  other  conditions,  of  being  metamorphosed 
into  Heat,  so  may  either  of  these  forces,  acting  under  conditions  which 
an  Organized  fabric  alone  can  supply,  be  converted  into  Vital  force, 
whilst,  in  their  turn,  they  may  be  generated  by  Vital  Force. 


GENERAL   SUMMARY.  57 

71.  Starting,  then,  with  the  abstract  notion  of  one  general  Force,  we 
might  say  that  this  Power,  operating  through  Inorganic  matter,  mani- 
fests itself  in  those  phenomena  which  we  call  electrical,  magnetical, 
chemical,  thermical,  optical,  or  mechanical ;  the  agents  immediately  con- 
cerned in  these  being  so  connected  by  the  relation  of  reciprocal  agency, 
or  "  correlation,"  that  we  must  regard  them  as  fundamentally  the  same. 
But  the  very  same  Force  or  Power,  when  directed  through  Organized 
structures,  effects  the  operations  of  growth,  development,  metamorphosis, 
and  the  like ;  and  is  further  transformed,  through  the  instrumentality 
of  the  structures  thus  generated,  into  nervous  agency  and  muscular 
power.  If  we  only  knew  of  Heat,  for  example,  as  it  acts  upon  the  or- 
ganized creation,  the  peculiarities  of  its  operation  upon  inorganic  matter 
would  seem  no  less  strange  to  the  physiologist,  than  the  effects  here 
attributed  to  it  may  appear  to  those  who  are  only  accustomed  to  con- 
template the  physical  phenomena  to  which  it  gives  rise.  Of  the  exis- 
tence of  Force  or  Power,  we  can  give  no  other  account  than  by  referring 
it,  as  we  are  led  by  our  own  consciousness  to  do,  to  the  exertion  of  a 
Will;  and  this  unity  among  the  Forces  of  Nature  is  the  strongest 
possible  indication  of  the  Unity  of  the  Will  of  which  they  are  the  ex- 
pressions. And  further,  the  constancy  of  the  actions  which  result  from 
them,  when  the  conditions  are  the  same, — that  is,  their  conformity  to  a 
fixed  plan,  or  (in  the  language  commonly  employed)  their  subordination 
to  laws, — indicates  the  constancy  and  unchangeableness  of  the  Divine 
Will,  as  well  as  the  Infinity  of  that  Wisdom,'  by  which  the  plan  was  at 
first  arranged  with  such  perfection,  as  to  require  no  departure  from  it, 
in  order  to  produce  the  most  complete  harmony  in  its  results. 

72.  So  also,  if  we  endeavour  to  assign  a  cause  for  the  existence  of  a 
cell-germ,  we  are  led  at  first  to  fix  upon  the  vital  operations  of  the  pa- 
rental organism  by  which  it  was  produced ;  and  for  these  we  can  assign 
no  other  cause  than  the  peculiar  endowments  of  its  original  germ, 
brought  into  activity  by  the  forces  which  have  operated  upon  it.  Thus 
we  are  obliged  to  go  backwards  in  idea  from  one  generation  to  another ; 
and  when  at  last  brought  to  a  stand  by  the  origin  of  the  race,  we  are 
obliged  to  rest  in  the  Divine  Will  as  the  source  of  those  wonderful  pro- 
perties, by  which  the  first  germ  developed  the  first  organism  of  that 
race  from  Materials  previously  unorganized,  this  organism  producing  a 
second  germ,  the  second  germ  a  second  organism,  and  so  on  without 
limit,  by  the  uniform  repetition  of  the  same  processes.  Yet  we  are  not 
to  suppose  that  the  continuation  of  the  race  is  really  in  any  way  less 
dependent  upon  the  Will  of  the  Creator,  than  the  origin  of  it.  For 
whilst  Science  leads  us  to  discard  the  idea  that  the  Deity  is  continually 
interfering,  to  change  the  working  of  the  system  He  has  made,— since 
it  everywhere  presents  us  with  the  idea  of  uniformity  in  the  plan,  and 
of  constancy  in  the  execution  of  it, — it  equally  discourages  the  notion 
entertained  by  some,  that  the  creation  of  matter,  endowed  with  certain 
properties,  and  therefore  subject  to  certain  actions,  was  the  final  act  of 
the  Deity,  as  far  as  the  present  system  of  things  is  concerned,  instead 
of  being  the  mere  commencement  of  his  operations.  If  it  be  admitted 
that  matter  owes  its  origin  and  properties  to  the  Deity,  or,  in  other 
words,  that  its  first  existence  was  but  an  expression  of  the  Divine  Will, 


58  EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

what  is  its  continued  existence,  but  a  continued  operation  of  the  same 
Will  ?  To  suppose  that  it  could  continue  to  exist,  and  to  perform  its 
various  actions,  by  itself,  is  at  once  to  assume  the  property  of  self-exist- 
ence as  belonging  to  matter,  and  thus  to  do  away  with  the  necessity  of 
a  Creator  altogether ; — a  conclusion  to  which  it  may  be  safely  affirmed 
that  no  ordinarily  constituted  Man  can  arrive,  who  reasons  upon  the 
indications  of  Mind  in  the  phenomena  of  Nature,  in  the  same  way  as  he 
does  in  regard  to  the  creations  of  Human  Art. 


CHAPTER  11. 

OP  THE  EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

73.  It  has  been  shown  in  the  preceding  Chapter,  that  the  most  general 
conditions  of  Vital  phenomena  are  twofold ; — one  set  being  supplied  by 
the  organized  structure,  which  is  endowed  (in  virtue  of  its  organization) 
with  certain  peculiar  properties,  but  which  is  inert  so  long  as  it  is  alto- 
gether secluded  from  the  influence  of  external  agents ; — whilst  the  other 
is  derived  from  external  sources,  and  consists  in  a  supply  of  those  ma- 
terials of  which  the  organized  structure  is  built  up,  and  in  the  operation 
of  iho^Q  forces  by  which  the  organism  is  made  to  appropriate  those  ma- 
terials, which  are  the  sources  of  its  peculiar  powers.  We  might  thus, 
in  a  rough  and  rude  way  it  is  true,  compare  the  living  body  to  a  set  of 
machinery  adapted  to  convert  cotton  from  the  raw  material  into  a  woven 
fabric.  Each  portion  of  the  machinery  does  its  own  special  work,  in 
virtue  of  its  peculiar  construction ;  e.  g.  one  part  cards,  another  spins, 
and  a  third  weaves  ;  but  their  actions  are  closely  related  and  even  mu- 
tually dependent.  Further,  their  operations  all  result  from  one  and  the 
same  force  or  power ;  and  their  products  may  consequently  be  regarded 
as  the  expressions  or  manifestations  of  that  Force,  which  acts  through 
the  diff'erent  portions  of  the  mechanism,  each  in  its  own  peculiar  mode. 
Now.  such  a  machine  can  produce  no  result,  without  the  concurrence  of 
these  conditions ;  namely,  the  perfectly  constructed  organism  (for  so  in 
the  wide  sense  of  the  term  it  may  be  designated),  a  supply  of  the  raw 
material  on  which  it  is  to  operate,  and  an  adequate  moving  power.  And 
it  is  to  be  observed,  that  the  amount  of  its  product  will  depend  rather 
upon  the  power,  than  upon  the  material  supplied ;  for  whilst  its  activity 
cannot  be  increased  by  any  augmentation  in  the  quantity  of  the  material, 
beyond  that  amount  which  it  has  power  to  employ,  it  can  be  promoted 
by  a  more  energetic  application  of  the  force,  as  well  as  retarded  by  its 
diminution ;  the  amount  of  material  appropriated  being  increased  or 
diminished  accordingly. 

74.  In  like  manner,  it  is  requisite  to  distinguish,  among  the  external 
conditions  whose  concurrence  is  necessary  to  produce  a  Living  Organism, 
between  those  which  furnish  the  materials  requisite  for  its  construction 
and  maintenance,  and  the  forces  or  powers  on  which  its  operations  are 
dependent ;  in  other  words,  between  the  Material  and  Dynamical  con- 


EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY.  59 

ditions  of  Vital  Activity.  Under  the  former  group  must  be  comprised, 
not  merely  the  Alimentary  substances  which  are  capable  of  being  con- 
verted into  portions  of  the  solid  fabric,  but  also  those  which  are  used 
(among  the  warm-blooded  animals)  for  the  maintenance  of  the  bodily 
heat  by  the  combustive  process.  In  addition,  we  have  to  include  the 
Water  which  is  requisite  to  maintain  the  due  proportion  of  liquid  in  the 
organized  fabric ;  and  the  Oxygen,  whose  presence  in  the  surrounding 
medium  is  essential  in  various  modes  to  the  maintenance  of  its  vital 
activity.  The  dependence  of  Vital  Activity  upon  Food  and  Oxygen 
will  be  fully  considered  hereafter  (chaps,  iv.  and  viii.);  and  in  the 
present  Chapter  it  will  be  only  necessary  to  take  account  of  the  demand 
for  Moisture  (Sect.  4). 

75.  The  Forces  to  whose  operation  we  can  most  clearly  trace  the 
phenomena  of  Life,  are  Light  and  Heat^  of  which  the  latter  is  the  one 
whose  agency  is  the  most  universal,  and  most  immediately  connected 
with  the  acts  of  growth  and  development.  The  agency  of  Light  is 
indispensable  for  the  first  production  of  organic  compounds  by  the  in- 
strumentality of  the  Vegetable  fabric ;  but  it  would  possess  no  efiicacy 
whatever,  without  the  simultaneous  operation  of  Heat ,  and  when  these 
compounds  have  been  generated,  we  find  that  they  can  be  applied  to 
the  purposes  of  Vegetable  nutrition,  no  less  than  to  the  nutrition  of 
Animals,  without  the  aid  of  Light ;  as  is  seen  in  the  fact,  that  the  ger- 
mination of  seeds  takes  place  in  darkness,  and  that  the  formation  of 
new  wood  in  a  stem  takes  place  beneath  a  thick  covering  of  bark.  A 
very  large  proportion  of  the  vital  operations  of  Animals  have  no  direct 
dependence  upon  Light ;  yet  it  is  entirely  through  its  operation  upon 
Plants,  that  they  derive  the  materials  of  their  nutriment ;  so  that  La- 
voisier was  fully  justified  in  the  assertion  that  "  without  Light,  nature 
were  without  life  and  without  soul ;  and  a  beneficent  God,  in  shedding 
light  over  creation,  strewed  the  surface  of  the  earth  with  organization, 
with  sensation,  and  with  thought."  As  an  example  of  the  very  direct 
relation  which  subsists  between  the  amount  of  Light  and  Heat  acting 
on  an  organism,  and  the  amount  of  vital  change  produced,  it  may  be 
well  to  advert  to  the  statement  of  Boussingault,  that  the  same  annual 
plant,  in  arriving  at  its  full  development,  and  going  through  the  process 
of  flowering  and  of  the  maturation  of  its  seed,  everywhere  requires  the 
same  amount  of  Light  and  Heat,  whether  it  be  grown  at  the  equator  or 
in  the  temperate  zone;  the  whole  time  occupied  being  inversely  to  the 
intensity  of  these  forces,  and  the  rate  of  growth  having  a  relation  of 
direct  equivalence  to  it. — We  have  little  certain  knowledge  of  the  degree 
of  the  ordinary  dependence  of  Vital  Activity  upon  Electricity  ;  although 
there  can  be  no  doubt  that  it  is  capable  of  exerting  a  most  important 
influence  upon  the  living  organism. 

76.  In  regard  to  all  these  Forces  it  may  be  observed,  that  the  de- 
pendence of  Vital  Action  upon  their  constant  influence  is  greater  in 
proportion  to  the  high  organization  of  their  structure,  and  vice  versd ; 
so  that  beings  of  simple  organization  are  capable  of  enduring  a  depri- 
vation of  them,  which  would  be  fatal  to  those  higher  in  the  scale.  This 
will  be  partly  understood,  when  it  is  borne  in  mind  that  the  higher  the 
development  of  the  living  being,  the  more  complete  is  the  distribution 


60  EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

of  its  diiFerent  actions  amongst  separate  organs, — the  more  close,  there- 
fore, is  their  mutual  dependence, — and  the  more  readily,  in  consequence, 
are  they  all  brought  to  a  close  by  the  interruption  of  any  one.  But 
there  is  no  doubt,  that  the  actions  of  even  the  individual  parts  of  the 
higher  organisms  require  for  their  excitement  a  greater  supply  of  these 
powers,  than  the  similar  actions  of  the  corresponding  parts  in  the  lower : 
whilst  if  these  forces  be  exerted  upon  the  lower  with  the  intensity  that 
is  required  for  the  higher,  they  destroy  the  vital  properties  of  the  tissues 
altogether,  by  the  excess  of  their  action.  This  distinction  is  most  ob- 
vious in  regard  to  the  relative  influence  of  Heat,  upon  warm-blooded 
and  cold-blooded  animals ;  of  which  examples  will  be  given  hereafter. 

77.  It  may  also  be  observed  of  the  influence  of  these,  as  of  that  of 
other  forces  whose  agency  is  less  general,  that  it  is  rather  relative  than 
absolute ;  being  frequently  dependent  upon  the  degree  of  change,  rather 
than  upon  the  measure  of  the  actual  amount.  This  constitutes  a  marked 
difierence  between  the  influence  of  these  forces  on  mere  chemical  com- 
pounds, and  their  operation  on  bodies  endowed  with  vitality.  In  the 
former  case  their  action  is  always  uniform ;  thus  the  same  amount  of 
heat,  the  same  exposure  to  light,  the  same  charge  of  electricity,  would 
be  required  to  produce  a  given  Chemical  efi'ect,  how  often  soever  the 
action  might  be  repeated.  But  this  is  not  the  case  with  living  bodies ; 
since  an  increase  or  diminution  in  the  intensity  of  Heat,  which,  if  made 
suddenly,  would  be  scarcely  compatible  with  the  continuance  of  Life, 
may  be  so  brought  about,  as  to  produce  no  marked  change  in  its  phe- 
nomena,— the  organism  possessing  a  certain  power  of  adapting  itself  to 
conditions  which  are  habitual  to  it,  and  thus  allowing  great  changes  in 
these  conditions  to  be  gradually  efi*ected,  without  any  serious  disturb- 
ance.— Thus  of  two  individuals  of  the  same  species,  one  may  become 
torpid  at  a  temperature  of  60°,  because  it  has  been  accustomed  to  a 
temperature  of  70°  ;  whilst  another,  habituated  to  a  temperature  of  60°, 
would  require  to  be  cooled  down  to  50°,  in  order  to  induce  torpidity; 
the  influence  of  temperature  upon  the  vital  condition  being  proportioned, 
more  to  the  variation  from  the  usual  standard,  than  to  the  actual  degree 
of  heat  or  cold  in  operation.  Yet  the  first  of  these  individuals  might 
be  gradually  habituated  to  live  in  the  same  temperature  with  the  second ; 
and  to  require  the  same  amount  of  further  depression  for  the  induction 
of  torpidity.     (See  §  132.) 

78.  It  is  a  very  curious  fact,  that,  whilst  the  lower  classes  of  living 
beings  are  more  capable  than  the  higher  of  bearing  the  deprivation  of 
these  Vital  stimuli,  they  are  at  the  same  time  more  liable  to  alterations 
in  their  own  structure  and  development,  in  consequence  of  variations 
in  the  degree  of  their  agency,  or  from  other  causes  external  to  them- 
selves. Thus  the  forms  of  the  lower  tribes  of  Plants  and  Animals  are 
liable  to  be  greatly  afi'ected  by  the  conditions  under  which  they  grow ; 
and  these  especially  modify  their  degree  of  development.  It  seems  as 
if  the  formative  power  were  less  vigorous  in  the  lower,  than  in  the 
higher  classes;  so  that  the  mode  in  which  it  manifests  itself  in  the 
former  is  more  dependent  upon  external  influences ;  whilst  in  the  latter 
it  either  predominates  over  them,  causing  the  regular  actions  to  be  per- 
formed, or  gives  way  altogether. — The  same  principle  applies  to  the 


LIGHT,   AS  A   CONDITION   OP  VITAL  ACTIVITY.  61 


% 


early  condition  of  the  higher  organisms ;  their  embryos,  like  those 
beings  of  permanently-low  type  which  they  resemble  in  degree  of  deve- 
lopment, being  liable  to  be  affected  by  modifying  causes,  which  the 
perfect  beings  of  the  same  kind  are  able  to  resist.  It  ig  in  this  way 
that  we  are  to  explain  the  influence  which  the  female  parent  exerts 
upon  the  embryo,  during  the  period  through  which  it  is  dependent  upon 
her  for  the  materials  for  its  development. 

1.    Of  Light  J  as  a  Condition  of  Vital  Activity. 

79.  The  importance  of  this  agent,  not  only  to  the  Vegetable  but  to 
the  Animal  World,  is  not  in  general  sufficiently  estimated.  Under  its 
influence  alone  can  that  fiirst  process  be  accomplished,  by  which  Inor- 
ganic matter  is  transformed  into  an  Organic  compound,  adapted  by  its 
nature  and  properties  to  form  part  of  the  organized  fabric.  The  fol- 
lowing is  an  example  of  the  simplest  phenomenon  of  this  kind  ;  and  it 
demonstrates  the  influence  of  Light  the  more  clearly  on  account  of  that 
simplicity.  "If  we  expose  some  spring-water  to  the  sunshine,  though 
it  may  have  been  clear  and  transparent  at  first,  it  presently  begins  to 
assume  a  greenish  tint ;  and,  after  a  while,  flocks  of  green  matter  col- 
lect on  the  sides  of  the  vessel  in  which  it  is  contained.  On  these  flocks, 
whenever  the  sun  is  shining,  bubbles  of  gas  may  be  seen,  which,  if  col- 
lected, prove  to  be  a  mixture  of  oxygen  and  nitrogen,  the  proportion 
of  the  two  being  variable.  Meanwhile  the  green  matter  rapidly  grows ; 
its  new  parts,  as  they  are  developed,  being  all  day  long  covered  with 
air-bells,  which  disappear  as  soon  as  the  sun  has  set.  If  these  observa- 
tions be  made  upon  a  stream  of  water,  the  current  of  which  runs  slowly, 
it  will  be  discovered  that  the  green  matter  serves  as  food  for  thousands 
of  aquatic  Insects,  which  make  their  habitations  in  it.  These  insects 
are  endowed  with  powers  of  rapid  locomotion,  and  possess  a  highly- 
organized  structure ;  in  their  turn  they  fall  a  prey  to  the  Fishes  which 
frequent  such  streams."*  Such  is  the  general  succession  of  nutritive 
actions  in  the  Organized  Creation.  The  highest  Animal  is  either 
directly  dependent  upon  the  Vegetable  Kingdom  for  the  materials  of 
its  fabric,  or  it  is  furnished  with  these  by  some  other  Animal,  this  again 
(it  may  be)  by  another,  and  so  on ;  the  last  in  the  series  being  always 
necessitated  to  find  its  support  in  the  Vegetable  kingdom,  since  the 
Animal  does  not  possess  the  power  of  causing  the  Inorganic  elements 
to  unite  into  even  the  simplest  Organic  compound.  This  power  is  pos- 
sessed in  a  high  degree  by  Plants ;  but  it  can  only  be  exercised  under 
the  influence  of  Light,  We  shall  now  examine,  more  in  detail,  the 
conditions  of  this  influence,  both  in  the  instance  just  quoted,  and  in 
others  drawn  from  the  actions  of  the  higher  Vegetable  organisms. 

80.  The  "green  matter  of  Priestley,"  (as  it  is  commonly  called), 
which  makes  its  appearance  when  water  of  average  purity  is  submitted 
to  the  action  of  the  Sun's  light,  and  which  also  presents  itself  on  the 
surface  of  walls  and  rocks  that  are  constantly  kept  damp,  is  now  known 
by  Botanists  to  consist  of  cells  in  various  stages  of  development, — the 

*  Prof.  Draper,  on  the  Forces  which  produce  the  Organization  of  Plants ;  p.  15. 


62  EXTERNAL  CONDITIONS   OF  VITAL  ACTIVITY. 


early  forms,  it  may  be,  of  several  different  species  of  Confervae.  That 
these  cells  all  originate  from  germs,  and  not  merely  from  a  combina- 
tion of  inorganic  elements,  appears  not  only  from  general  considera- 
tions, but  also  from  the  fact  that,  if  measures  be  taken  to  free  the  water 
entirely  from  any  possible  infusion  of  organic  matter,  and  to  admit  into 
contact  with  it  such  air  alone  as  has  undergone  a  similar  purification, 
no  green  flocks  make  their  appearance,  under  the  prolonged  influence 
of  the  strongest  sunlight.  We  find,  then,  that  the  presence  of  a  germ 
is  one  of  the  conditions  indispensable  to  the  chemical  transformation  in 
question.  It  may  be  asked  how  it  can  be  certainly  ascertained  that 
lights  and  not  heat,  is  the  essential  condition  of  this  process ;  seeing 
that  the  two  agents  are  combined  in  the  solar  beam.  To  this  it  may 
be  replied,  that  a  certain  moderate  amount  of  heat  is  undoubtedly  ne- 
cessary ;  but  that  no  degree  of  heat  without  light  will  be  effectual  in 
producing  the  change,  as  is  easily  proved  by  exposing  the  water  to 
warmth  in  a  dark  place.  Moreover,  when  a  certain  measure  of  light  is 
afforded,  variations  in  the  amount  of  heat  make  very  little  difference ; 
but  we  shall  presently  see  that  under  the  same  degree  of  heat,  the 
amount  of  the  change  is  directly  proportional  to  the  intensity  of  the 
light.  Although,  therefore,  heat  furnishes  an  essential  condition,  it 
cannot  be  questioned  that  light  is  the  chief  agent  in  the  process,  by 
which  the  germ  brings  into  union  the  elements  to  be  employed  in  the 
development  of  its  own  fabric. 

81.  The  next  question  is, — What  are  these  elements,  and  whence  are 
they  obtained  ?  All  water  that  is  long  exposed  to  the  atmosphere  ab- 
sorbs from  it  a  certain  amount  of  its  constituent  gases ;  but  these  do 
not  enter  it  in  the  proportions  in  which  they  are  contained  in  the 
atmosphere  itself;  their  relative  quantities,  in  a  given  measure  of  water, 
being  proportional  to  the  facility  with  which  they  are  respectively  ab- 
sorbed by  the  liquid.  Thus,  carbonic  acid  is  most  readily  absorbable  ; 
oxygen  next,  and  nitrogen  least  so.  From  the  experiments  of  Prof. 
Draper,  it  would  appear  that,  notwithstanding  the  very  small  propor- 
tion of  carbonic  acid  contained  in  the  atmosphere  (usually  not  more 
than  l-2000th  part),  it  forms  as  much  as  29  per  cent,  of  the  whole 
amount  of  air  expelled  from  water  by  boiling.  Of  the  residue,  one-third 
consists  of  oxygen,  and  the  remaining  two-thirds  of  nitrogen ;  so  that 
the  proportion  of  the  oxygen  to  the  nitrogen  is  as  one  to  two,  instead 
of  being  one  to  four,  as  in  atmospheric  air.  The  absolute  quantity  of 
this  water-gas,  contained  in  any  measure  of  water,  is  subject  to  varia- 
tion with  the  temperature ;  the  quantity  being  diminished  as  the  tem- 
perature rises.  Now  when  water  thus  impregnated  with  carbonic  acid, 
oxygen,  and  nitrogen,  and  containing  the  germs  of  aquatic  plants,  is 
exposed  to  the  sun's  light,  a  development  of  vegetable  structure  takes 
place,  indicated  by  the  green  flocculent  appearance,  as  already  men- 
tioned. If  the  changes,  which  are  now  occurring  in  the  water,  be  ex- 
amined, we  find  that  the  carbonic  acid  is  diminishing  in  amount ;  and 
that  oxygen  is  being  evolved.  The  growing  mass  increases  in  volume 
and  weight ;  and  after  a  time  exhausts  the  whole  carbonic  acid  origi- 
nally contained  in  the  water.  If  it  be  then  prevented  from  receiving 
an  additional  supply,  the  process  stops ;  but  as  conducted  naturally, 


INFLUENCE   OP  LIGHT  ON   PLANTS.  63 

there  is  a  free  exposure  to  the  atmosphere,  through  which  carbonic  acid 
is  diffused ;  and  hence,  as  fast  as  it  is  removed  by  decomposition,  it  is 
restored  by  absorption. 

82.  Here  then  are  the  conditions  and  materials ;  what  i^  the  result  ? 
As  a  consequence  of  the  conjoint  action  of  light  and  of  a  vegetable  cell- 
germ,  with  a  moderate  degree  of  heat,  upon  carbonic  acid  and  water, 
we  find  a  vegetable  structure  produced,  whose  fabric  chiefly  consists  of 
carbon,  united  with  the  elements  of  water.  Whether  this  union  is  really 
as  simple  and  direct  as  is  implied  by  this  expression,  or  whether  the 
same  proportions  of  ogygen,  hydrogen,  and  carbon  are  united  in  a  dif- 
ferent form,  is  not  a  matter  of  consequence  to  the  present  inquiry ;  the 
general  fact  being,  that  by  the  decomposition  of  the  carbonic  acid,  oxy- 
gen is  set  free,  and  carbon  is  made  to  unite  with  the  elements  of  water ; 
so  as  to  form  an  organic  compound,  which  is  appropriated  by  the  Vege- 
table organism  as  the  material  for  its  growth. — How  far  Light  is  also 
concerned  in  the  production  of  the  proteine-compounds  which  are  gene- 
rated by  Plants,  not  merely  for  the  use  of  Animals,  but  also  as  part 
of  the  material  of  their  own  growth,  has  not  been  yet  ascertained ;  but 
it  is  probable  that  these  are  not  the  less  dependent  upon  its  agency  for 
their  formation,  since  they  are  formed  under  the  same  circumstances 
with  the  preceding. 

83.  The  process  whose  conditions  we  have  thus  examined,  is  carried 
on  in  the  individual  cells,  that  compose  the  highest  and  most  complex 
Plants,  precisely  as  in  those  which  constitute  the  entire  organisms  of  the 
lowest.  Thus  if  a  few  garden-seeds  of  any  kind  be  sown  in  a  flower-pot, 
and  be  caused  to  germinate  in  a  dark  room,  it  will  soon  be  perceived 
that  although  they  can  grow  for  a  time  without  the  influence  of  light,  that 
time  is  limited  ;  the  weight  of  their  solid  contents  diminishes,  although 
their  hulk  may  increase  by  the  absorption  of  water ;  their  young  leaves, 
if  any  should  be  put  forth,  are  of  a  yellow  or  gray-white  colour,  and 
they  soon  fade  away  and  die.  But  if  these  plants  are  brought  out  suffi- 
ciently soon  into  the  bright  sunlight,  they  speedily  begin  to  turn  green, 
they  unfold  their  leaves,  and  evolve  their  different  parts  in  a  natural 
way ;  and  the  proportion  of  their  solid  contents  goes  on  increasing  from 
day  to  day.  If  the  fabric  be  then  subjected  to  chemical  analysis,  it  is 
found  to  contain  oxygen,  hydrogen,  carbon,  and  nitrogen ;  united  in 
various  proportions,  so  as  to  form  compounds  that  differ  in  the  various 
species,  though  some, — such  as  gum,  starch,  cellulose,  and  albuminous 
matter, — are  the  same  in  all.  If  the  plants  be  made  to  grow  in  closed 
glass  vessels,  under  such  circumstances  that  an  examination  can  be 
accurately  made  as  to  the  changes  they  are  impressing  on  the  atmo-^ 
sphere,  it  is  discovered  that  they  are  constantly  decomposing  its  carbonic 
acid, — appropriating  its  carbon,  and  setting  free  its  oxygen, — so  long 
as  they  are  exposed  to  the  influence  of  sunshine  or  bright  daylight. 
They  also  appropriate  a  part  of  the  minute  quantity  of  ammonia  which 
is  diffused  through  the  atmosphere ;  extracting  its  nitrogen  to  employ 
it  in  the  production  of  their  azotized  compounds.  It  is  capable  of  being 
demonstrated  by  experiment,  that  these  changes  are  confined  to  the  green 
surfaces  of  plants,  and  therefore  to  the  leaves  or  leaf-like  organs,  to  the 
young  shoots,  and  to  the  stems  of  herbaceous  plants,  or  of  those  in  which 


64  EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

(as  in  the  Cactus  tribe)  the  leaves  are  wanting  and  the  enlarged  succu- 
lent stem  supplies  their  place.  When  these  surfaces  cease  to  become 
green,  the  decomposing  action  also  ceases ;  carbon  is  no  longer  fixed 
and  oxygen  set  free ;  but,  on  the  contrary,  carbonic  acid  is  exhaled : 
this  is  the  case  when  the  leaves  change  colour,  previously  to  their  fall, 
in  the  autumn.  The  compounds  which  are  thus  generated  in  the  green 
surfaces,  are  conveyed  to  the  remote  parts  of  the  fabric,  by  the  circu- 
lation of  the  sap,  and  become  the  materials  of  their  nutrition ;  and  thus 
the  green  cells  of  the  leaves  have  exactly  the  same  function,  in  minis- 
tering to  the  growth  of  the  fabric  of  the  largest  tree,  which  the  green 
cells  of  the  humble  Conferva  perform  in  regard  to  themselves  alone. 

84.  It  has  been  already  mentioned,  that  the  decay  which  is  always 
taking  place  in  the  softer  vegetable  structures,  gives  rise  to  a  continual 
production  of  carbonic  acid,  even  in  the  living  plant ;  this  process,  which 
must  be  regarded  as  a  true  Respiration,  is  effected,  as  in  Animals,  by 
the  union  of  the  carbon  of  the  Plant  with  oxygen  derived  from  the  atmo- 
sphere ;  and  it  is  carried  on,  not  by  the  green  parts  only,  but  also,  per- 
haps chiefly,  by  the  darker  surfaces.  Being  antagonized  during  the 
day  by  the  converse  change  just  described,  it  can  only  be  made  sensible, 
by  placing  the  plants  for  a  time  in  an  atmosphere  in  which  no  carbonic 
acid  previously  existed;  and  it  will  then  be  found  that,  even  in  full 
daylight,  a  certain  amount  of  that  gas  is  exhaled.  The  fact,  however, 
becomes  much  more  obvious  at  night,  or  in  darkness ;  since  the  decom- 
position of  the  surrounding  carbonic  acid  by  the  green  surfaces  is  then 
completely  at  a  stand,  and  the  full  effect  of  the  respiratory  process  is 
seen.  Moreover,  when  a  plant  becomes  unhealthy,  from  too  long  con- 
finement in  a  limited  atmosphere,  it  begins  to  exhale  more  carbonic  acid 
than  it  decomposes ;  and  the  same  is  the  case,  as  just  now  stated,  in 
regard  to  leaves  that  have  nearly  reached  the  term  of  their  lives.  It 
does  not  admit  of  question,  however,  that,  under  ordinary  circumstances, 
nearly  the  whole  carbon  of  a  slow-growing  plant  is  derived  from  the  car- 
bonic acid  of  the  atmosphere ;  either  directly  through  the  leaves,  or 
indirectly  by  absorption  through  the  roots ;  and  that  there  must  be  a 
vast  surplus,  therefore,  of  the  carbonic  acid  decomposed,  over  that  which 
is  exhaled,  during  the  whole  life  of  the  tree, — that  surplus  being  in  fact 
represented  by  the  total  amount  of  carbon  contained  in  its  tissues. 

85.  It  is  probable  that  the  minute  amount  of  Carbonic  Acid  at  present 
contained  in  the  atmosphere,  is  as  much  as  could  be  beneficially  supplied 
to  Plants,  under  the  average  amount  of  light  to  which  they  are  sub- 
jected, over  the  whole  globe,  and  throughout  the  year.  It  has  been 
clearly  shown,  that,  under  the  influence  of  strong  sunlight,  an  atmo- 
sphere containing  as  much  as  7  or  8  per  cent,  of  carbonic  acid  may  be 
not  merely  tolerated  by  Plants,  but  may  be  positively  beneficial  to  them, 
producing  a  great  acceleration  in  their  growth ;  but  as  soon  as  the  light 
is  withdrawn,  it  acts  upon  them  most  injuriously,  causing  them  speedily 
to  become  unhealthy,  and  , altogether  destroying  their  vitality,  if  they 
are  long  subjected  to  it.  Under  more  cloudless  skies  than  ours,  how- 
ever, the  continual  supply  of  a  larger  quantity  of  carbonic  acid,  than 
our  atmosphere  contains,  is  found  to  be  quite  compatible  with  healthy 
vegetation ;  especially  in  the  case  of  Cryptogamic  plants,  which  (as  will 


INFLUENCE   OF   LIGHT   ON    PLANTS.  65 

be  presently  shown)  require  a  less  amount  of  this  agent  than  those  of  a 
higher  kind.  Thus  in  the  lake  Solfatara  in  Italy,  an  unusual  supply 
of  carbonic  acid  is  afforded  by  the  constant  escape  of  that  gas  from 
fissures  in  the  bed  of  the  lake,  with  a  violence  that  gives  to  the  water 
an  appearance  of  ebullition ;  and  on  its  surface  there  are  numerous 
floating  islands,  which  consist  almost  entirely  of  Confervae  and  other 
simple  cellular  plants,  growing  most  luxuriantly  on  this  rich  pabulum. 
And  it  has  been  remarked,  that  the  vegetation  around  the  springs  in 
the  valley  of  Gottingen,  which  abound  in  carbonic  acid,  is  very  rich  and 
luxuriant ;  appearing  several  weeks  earlier  in  the  spring,  and  continuing 
much  later  in  the  autumn,  than  at  other  spots  in  the  same  district. 
Many  circumstances  lead  to  the  belief,  that  at  former  epochs  in  the 
Earth's  history,  the  atmosphere  was  much  more  highly  charged  with 
carbonic  acid  than  at  present ;  and  that  to  this  circumstance,  in  con- 
junction with  a  more  intense  and  constant  influence  of  light  and  heat,  we 
are  to  attribute  that  extraordinary  luxuriance  of  the  vegetation  of  those 
periods,  of  which  we  have  most  abundant  evidence,  in  the  vast  beds  of 
disintegrated  vegetable  matter — Coal — that  are  of  such  value  to  Man, 
and  in  the  remains  which  have  been  more  perfectly  preserved  to  us,  and 
which  indicate  that  not  only  the  general  forest  mass,  but  many  of  the 
individual  forms,  attained  a  degree  of  development,  which  cannot  now 
be  paralleled  even  between  the  Tropics. 

86.  Various  experiments  have  been  recently  made,  with  the  view  of 
determining  more  precisely  the  conditions  under  which  Light  acts,  in 
producing  the  chemical  changes  that  have  been  now  discussed.  These 
experiments  for  the  most  part  agree  in  the  very  interesting  result,  that 
the  amount  of  carbonic  acid  decomposed  by  plants  subjected  to  the  dif- 
ferently-coloured rays  of  the  solar  spectrum,  but  otherwise  placed  in 
similar  circumstances,  varies  with  the  illuminating  power  of  the  rays, 
and  not  with  their  heating  or  their  chemical  power.  The  method  adopted 
by  Prof.  Draper,  which  seems  altogether  the  most  satisfactory,  consisted 
in  exposing  leaves  of  grass,  in  tubes  filled  with  water  which  had  been 
saturated  with  carbonic  acid  (after  the  expulsion  of  the  previously  dis- 
solved air  by  boiling),  to  the  influence  of  the  different  rays  of  the  solar 
spectrum,  dispersed  by  a  prism ;  these  were  kept  motionless  upon  the 
tubes  for  a  sufl&cient  length  of  time  to  produce  an  active  decomposition 
of  the  gas  in  the  tubes  which  were  most  favourably  influenced  by  the 
solar  beams ;  and  the  relative  quantities  of  the  oxygen  set  free  were 
then  measured.  It  was  then  evident  that  the  action  had  been  almost 
entirely  confined  to  two  of  the  tubes,  one  of  them  being  placed  in  the 
red  and  orange  part  of  the  spectrum,  and  the  other  in  the  yellow  and 
green.  The  quantity  of  carbonic  acid  decomposed  by  the  plant  in  the 
latter  of  these,  was  to  that  decomposed  in  the  former,  in  the  ratio  of 
nine  to  five  ;  the  quantity  found  in  the  tube  that  had  been  placed  in  the 
green  and  blue  portion  of  the  spectrum,  would  not  amount,  in  the  same 
proportion,  to  one;  and  in  the  other  tubes,  it  was  either  absolutely 
nothing,  or  extremely  minute.  Hence  it  is  obvious  that  the  yellow  ray, 
verging  into  orange  on  one  side,  and  into  green  on  the  other,  is  the 
situation  of  the  greatest  exciting  power  possessed  by  light  on  this  most 
important  function  of  plants ;  and  as  this  coincides  with  the  seat  of  the 

6 


66  EXTERNAL   CONDITIONS   OF  VITAL   ACTIVITY. 

greatest  illuminating  power  of  the  spectrum,  it  can  scarcely  be  doubted 
that  light  is  the  agent  here  concerned ;  more  especially  as  the  place  of 
greatest  heat  is  in  the  red  ray,  and  that  of  greatest  chemical  power  is 
in  the  hlue^  both  of  which  rays  were  found  to  be  quite  inert  in  the  ex- 
periment just  quoted.  It  must  not  be  supposed  from  this  experiment, 
however,  that  the  yellow  ray,  and  those  immediately  adjoining  it,  are 
the  only  sources  of  this  power  in  the  Solar  spectrum ;  since  it  proves 
no  more  than  that,  when  the  leaves  were  exposed  to  a  highly  carbonated 
atmosphere,  they  could  only  decompose  it  under  the  influence  of  these 
rays.  It  is  certain,  from  other  experiments,  that  plants  will  grow,  in 
an  ordinary  atmosphere,  under  rays  of  different  colours ;  and  it  appears 
that  the  amount  of  carbon  they  severally  fix,  bears  a  constant  proportion 
to  the  illuminating  powers  of  the  respective  rays. 

87.  Although  this  fixation  of  carbon  by  the  decomposition  of  carbonic 
acid,  is  the  most  universally  dependent,  of  all  the  processes  of  the  Vege- 
table economy,  upon  the  influence  of  Light,  yet  it  is  not  the  only  one, 
especially  among  the  higher  Plants,  in  which  that  agent  becomes  an 
important  condition.  Of  the  whole  quantity  of  moisture  imbibed  by  the 
roots,  and  contained  in  the  ascending  sap,  a  large  proportion  is  exhaled 
again  by  the  leaves ;  a  small  part  only  being  retained  (together  with 
the  substances  previously  dissolved  in  the  whole)  to  form  part  of  the 
fabric.  Now  upon  the  rapidity  of  this  Exhalation  depends  the  rapidity 
of  the  absorption ;  for  the  roots  will  not  continue  to  take  up  more  than 
a  very  limited  amount  of  fluid,  when  it  is  not  discharged  again  from  the 
opposite  extremity  (so  to  speak)  of  the  stem.  The  loss  of  fluid  by  the 
leaves  appears  to  be  a  simple  process  of  evaporation,  depending  in  great 
part  upon  the  temperature  and  dryness  of  the  surrounding  air ;  this 
evaporation,  however,  does  not  take  place  solely,  or  even  chiefly,  from 
the  external  surface  of  the  leaves,  but  from  the  walls  of  the  passages 
which  are  channeled-out  in  their  interior.  Into  this  complex  labyrinth, 
the  outer  air  finds  its  way  through  orifices  in  the  cuticle,  which  are 
termed  stomata;  and  through  these  it  comes  forth  again,  charged  with 
a  large  amount  of  vapour  communicated  to  it  by  the  extensive  moist 
surface,  with  which  it  comes  into  contact  in  the  interior  of  the  leaf.  Now 
the  stomata  are  bounded  by  two  or  more  cells,  in  such  a  manner  that  they 
can  be  opened  or  closed  by  changes  in  the  form  of  these ;  and  this  alte- 
ration is  regulated  by  the  amount  of  Light,  to  which  the  leaves  are  sub- 
jected. When  the  stomata  are  opened  under  the  influence  of  light,  the 
external  air  is  freely  admitted  to  the  extended  surface  of  moist  tissue 
within  the  leaf,  and  a  rapid  loss  of  fluid  is  the  result ;  more  especially 
if  the  temperature  be  high,  and  the  atmosphere  in  a  dry  state.  On  the 
other  hand,  if  the  stomata  be  closed,  the  only  loss  of  fluid  that  can  take 
place  from  the  internal  tissue  of  the  leaves,  is  through  the  cuticle ;  the 
organization  of  which  seems  destined  to  enable  it  to  resist  evaporation, 
so  that  the  exhalation  is  almost  entirely  checked.  The  influence  of 
light  upon  this  important  function  is  easily  shown  by  experiment.  If 
a  plant,  which  is  actively  transpiring  and  absorbing  under  a  strong  sun- 
shine, be  carried  into  a  dark  room,  both  these  operations  are  almost 
immediately  checked,  even  though  the  surrounding  temperature  be  higher 
than  that  to  which  the  plant  w^as  previously  exposed. 


INFLUENCE  OF  LIGHT  ON  PLANTS.  67 

88.  The  effect  of  the  complete  and  continued  withdrawal  of  Light 
from  a  growing  plant,  is  to  produce  an  etiolation  or  blanching  of  its 
green  surfaces :  a  loss  of  weight  of  the  solid  parts,  owing  to  the  conti- 
nued disengagement  of  carbon  from  its  tissues,  unbalanced  by  the  fixa- 
tion of  that  element  from  the  atmosphere ;  a  dropsical  distension  of  the 
tissues,  in  consequence  of  the  continued  absorption  of  water,  which  Js 
not  got  rid  of  by  exhalation ;  a  want  of  power  to  form  its  peculiar  secre- 
tions, or  even  to  generate  new  tissues,  after  the  materials  previously 
stored  up  have  been  exhausted ;  in  fine,  a  cessation  of  all  the  operations 
most  necessary  to  the  preservation  of  the  vitality  of  the  structure,  of 
which  cessation  its  death  is  the  inevitable  result.  A  partial  withdrawal 
of  the  influence  of  light,  however,  is  frequently  used  by  the  Cultivator, 
as  a  means  of  giving  an  esculent  character  to  certain  Plants,  which 
would  be  otherwise  altogether  uneatable ;  for  in  this  manner  their  tis- 
sues are  rendered  more  succulent  and  less  "stringy,"  whilst  their  pecu- 
liar secretions  are  formed  in  diminished  amount,  and  communicate  an 
agreeable  flavour  instead  of  an  unwholesome  rankness  of  taste. 

89.  There  is  one  period  in  the  life  of  the  Flowering  Plant,  however, 
in  which  the  influence  of  Light  is  rather  injurious  than  beneficial ;  this 
is  during  the  first  part  of  the  process  of  germination  of  seeds,  which  is 
decidedly  retarded  by  its  agency.  This  forms  no  exception,  however, 
to  the  general  rule ;  since  the  decomposition  of  the  carbonic  acid  of  the 
atmosphere,  and  the  fixation  of  carbon  in  the  tissues,  do  not  constitute 
a  part  of  the  operation.  On  the  contrary,  the  embryo  being  nourished, 
like  an  animal,  by  organic  compounds  previously  elaborated  and  stored 
up  in  the  seed,  the  chemical  changes  which  take  place  in  them  involve 
the  opposite  action, — the  extrication  of  carbon,  which  is  converted  into 
carbonic  acid  by  uniting  with  the  oxygen  of  the  atmosphere.  It  is 
obvious,  then,  why  light  should  not  only  be  useless,  but  even  prejudicial, 
to  this  process ;  since  it  tends  to  fix  the  carbon  in  the  tissues,  which 
ought  to  be  thrown  off.  As  soon,  however,  as  the  cotyledons  or  seed- 
leaves  are  unfolded,  the  influence  of  light  upon  them  becomes  as  impor- 
tant, as  it  is  on  the  ordinary  leaves  at  a  subsequent  time ;  their  surfaces 
become  green,  and  the  fixation  of  carbon  from  the  atmosphere  com- 
mences. Up  to  that  point,  the  young  plant  is  diminishing  day  by  day 
(like  a  plant  that  is  undergoing  etiolation),  in  the  weight  of  its  solid 
contents ;  although  its  bulk  has  increased  by  the  absorption  of  water. 
From  the  time,  however,  that  its  cotyledons  begin  to  act  upon  the  air, 
under  the  influence  of  light,  the  quantity  of  solid  matter  begins  to  in- 
crease ;  and  its  augmentation  subsequently  takes  place,  at  a  rate  pro- 
portional to  the  amount  of  green  surface  exposed,  and  the  degree  of 
light  to  which  it  is  subjected* 

90.  The  influence  of  Light  upon  the  direction  of  the  growing  parts 
of  Plants,  upon  the  opening  and  closing  of  flowers,  &c.,  is  probably 
due  to  its  share  in  the  operations  already  detailed.  Thus  the  green 
parts  of  Plants,  or  those  which  effect  the  decomposition  of  carbonic 
acid  (such  as  the  leaves  and  stems),  have  a  tendency  to  grow  towards 
the  light ;  whilst  the  roots,  through  whose  dark  surfaces  carbonic  acid 
is  thrown  out  by  respiration,  have  an  equal  tendency  to  avoid  it. 
That  the  first  direction  of  the  stems  and  roots  of  plants  is  very  much 


68  EXTEKNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

influenced  in  this  manner,  appears  from  the  fact,  that,  by  reflecting 
light  upon  germinating  seeds,  in  such  a  manner  as  that  it  shall  only 
fall  upon  them  from  below,  the  stems  are  caused  to  direct  themselves 
downwards,  whilst  the  roots  grow  upwards. — There  can  be  no  doubt, 
however,  that  Light  has  also  a  more  direct  influence  on  the  develop- 
ment of  particular  organs  in  certain  Vegetables.  Thus  when  the  gem- 
mules'^  of  the  Marchantia  polymorpJia  (one  of  the  Hepaticce  or  Liver- 
worts), are  in  process  of  development,  it  has  been  shown  by  repeated 
experiments,  that  stomata  are  formed  on  the  side  exposed  to  the  light, 
and  that  roots  grow  from  the  lower  surface ;  and  that  it  is  a  matter  of 
indiff"erence  which  side  of  the  little  disk  is  at  first  turned  upwards, 
since  each  has  the  power  of  developing  stomata,  or  roots,  according  to 
the  influence  it  receives.  After  the  tendency  to  the  formation  of  these 
organs  has  once  been  given,  however,  by  the  sufiiciently  prolonged  in- 
fluence of  light  upon  one  side,  and  of  darkness  and  moisture  upon  the 
other,  any  attempt  to  alter  it  is  found  to  be  vain ;  for  if  the  surfaces 
be  then  inverted,  they  are  soon  restored  to  their  original  aspect  by  the 
twisting  growth  of  the  plant. 

91.  The  same  amount  of  this  agent  is  not  requisite  or  desirable  for 
all  Plants  ;  and  we  find  in  the  difi'erent  habitats  which  are  characteristic 
of  diff'erent  species,  even  amongst  our  native  plants,  that  the  amount 
congenial  to  each  varies  considerably.  Generally  speaking,  the  succu- 
lent thick-leaved  Plants  require  the  largest  amount ;  their  stomata  are 
few  in  number ;  and  the  full  influence  of  light  is  requisite  to  induce 
sufficient  activity  in  the  exhaling  process ;  accordingly  we  find  them 
growing,  for  the  most  part,  in  exposed  situations,  where  there  is  nothing 
to  interfere  with  the  full  influence  of  the  solar  rays.  On  the  other 
hand,  plants  with  thinner  and  more  delicate  leaves,  in  which  the  ex- 
haling process  is  easily  excited  to  an  excessive  amount,  evidently  find 
a  congenial  home  in  more  sheltered  situations ;  and  there  are  some 
which  can  only  develope  themselves  in  full  luxuriance  in  the  deep  shades 
of  a  plantation  or  a  forest.  By  a  further  adaptation  of  the  same  kind, 
some  species  of  Plants  are  enabled  to  live  and  acquire  their  green  colour 
under  an  amount  of  deprivation  which  would  be  fatal  to  most  others ; 
thus  in  the  mines  of  Freyburg,  in  which  the  quantity  of  light  admitted 
must  be  almost  infinitesimally  small,  Humboldt  met  with  Flowering 
Plants  of  various  species ;  and  Mustard  and  Cress  have  been  raised  in 
the  dark  abysses  of  the  collieries  of  this  country. 

92.  Generally  speaking,  however,  the  Cryptogamia  would  seem  to 
be  better  adapted  than  Flowering  Plants  to  carry  on  their  vegetating 
processes  under  a  low  or  very  moderate  amount  of  this  agency.  Thus 
Humboldt  found  a  species  of  sea-weed  near  the  Canaries,  which  pos- 
sessed a  bright  grass-green  hue,  although  it  had  grown  at  a  depth  of 
190  feet  in  the  sea,  where,  according  to  computation,  it  could  have 
received  only  1-1 500th  part  of  the  solar  rays  that  would  have  fallen 
upon  it  at  the  surface  of  the  ocean.     Many  Ferns,  Mosses,  and  Lichens 

*  These  gemmules  are  analogous  to  the  buds  of  higher  plants ;  and  they  consist  of 
little  collections  of  cells,  arranged  in  the  form  of  flat  disks  ;  which  are  at  first  attached 
by  footstalks  to  the  parent  plant,  but  afterwards  fall  off,  and  are  developed  into  new 
individuals. 


INFLUENCE  OF  LIGHT  ON  PLANTS.  69 

seem  as  if  they  avoided  the  light,  choosing  the  northern  rather  than  the 
southern  sides  of  hedges,  buildings,  &c.,  for  their  residence;  so  that 
the  former  often  present  a  luxuriant  growth  of  Cryptogamic  vegetation, 
whilst  the  latter  are  comparatively  bare.  It  must  not  he  supposed, 
however,  that  they  avoid  light  altogether,  but  only  what  is  to  them  an 
excessive  degree  of  it.  The  avoidance  of  light  seems  to  be  much 
stronger  in  the  Fungi,  which  grow  most  luxuriantly  in  very  dark 
situations ;  and  the  reason  of  this  is  probably  to  be  found  in  the  fact 
that,  like  the  germinating  seed  (§  89),  they  form  rather  than  decom- 
pose carbonic  acid ;  their  food  being  supplied  to  them  from  the  decay- 
ing substances  on  which  they  grow ;  and  the  rapid  changes  in  their 
tissues  giving  rise  to  a  high  amount  of  Respiration, — a  change  exactly 
the  converse  of  that,  on  which,  as  we  have  seen,  Light  exerts  such  a 
remarkable  power. 

93.  In  regard  to  the  agency  of  Light  upon  the  functions  of  Animals, 
comparatively  little  is  certainly  known.  It  is  evident  that  the  influence 
it  exerts  on  those  chemical  processes  which  constitute  the  first  stage  of 
Vegetable  nutrition,  can  have  scarcely  any  place  in  Animals ;  because  they 
do  not  perform  any  such  acts  of  combination,  but  make  use  of  the  pro- 
ducts already  prepared  for  them  by  Plants.  Hence,  we  do  not  find 
that  the  surface  of  Animals  undergoes  that  extension,  for  the  purpose 
of  being  exposed  to  the  solar  rays,  which  is  so  characteristic  a  feature 
in  the  Vegetable  fabric,  and  so  important  in  its  economy.  Still  there 
can  be  no  doubt,  that  the  degree  of  exposure  to  light  has  a  great 
influence  upon  the  colours  of  the  Animal  surface ;  and  here  we  seem  to 
have  a  manifestation  of  Chemical  agency,  analogous  to  that  which  gives 
colour  to  the  Vegetable  surface.  Thus  it  is  a  matter  of  familiar  expe- 
rience, that  the  influence  of  light  upon  the  skin  of  many  persons,  causes 
it  to  become  spotted  with  brown  freckles  ;  these  freckles  being  aggre- 
gations of  brown  pigment  cells,  which  either  owed  their  development  to 
the  agency  of  light,  or  were  enabled  by  that  agency  to  perform  a  che- 
mical transformation  which  they  could  not  otherwise  efi"ect.  In  like 
manner,  the  swarthy  hue,  which  many  persons  acquire  in  warm  cli- 
mates, is  due  to  a  development  of  dark  pigment-cells  diffused  through 
the  epidermis  (§  229) ;  and  an  increased  development  of  the  same  kind 
gives  rise  to  the  blackness  of  the  Negro-skin.  There  can  be  no  doubt 
that  the  prolonged  influence  of  light  upon  one  generation  after  another, 
tends  to  give  a  permanent  character  to  this  variety  of  hue ;  which  will 
probably  be  more  easily  acquired,  in  proportion  to  the  previously-exist- 
ing tendency  to  that  change.  Thus  it  is  well  known  that  a  colony  of 
Portuguese  Jews,  which  settled  at  Tranquebar  about  three  centuries 
ago,  and  which  has  kept  itself  distinct  from  the  surrounding  tribes,  can- 
not now  be  distinguished  as  to  colour  from  the  native  Hindoos.  But  it 
is  probable  that  a  similar  colony  of  fair-skinned  Saxons  would  not,  in 
the  same  time,  have  acquired  anything  like  the  same  depth  of  colour  in 
their  skins. 

94.  It  can  scarcely  be  questioned,  that  the  brilliancy  of  colour  which 
is  characteristic  of  many  tribes  of  animals  in  tropical  climates,  especially 
Birds  and  Insects,  is  in  great  part  dependent,  like  the  brightness  of  the 
foliage  and  fruit  of  the  same  countries,  upon  the  brightness  of  the  light 


70  EXTERNAL  CONDITIONS   OF  VITAL  ACTIVITY. 

to  ivhich  their  surfaces  are  exposed.  When  birds  of  warm  climates, 
distinguished  by  the  splendour  of  their  plumage,  are  reared  under  an 
artificial  temperature  in  our  own  country,  it  is  uniformly  observed  that 
they  are  much  longer  in  acquiring  the  hues  characteristic  of  the  adult ; 
and  that  these  are  never  so  bright  as  when  they  have  been  produced 
by  the  influence  of  the  tropical  sun.  And  it  has  been  also  remarked, 
that  if  certain  Insects  (the  Cockroach  for  example),  which  naturally 
inhabit  dark  places,  be  reared  in  an  entire  seclusion  from  light,  they 
grow  up  almost  as  colourless  as  Plants  that  are  made  to  vegetate  under 
similar  circumstances. 

95.  There  is  reason  to  believe  that  Light  exercises  an  important  in- 
fluence on  certain  processes  of  development  in  Animals,  as  well  as  in 
Plants.  Thus,  the  appearance  of  Animalcules  in  infusions  of  decaying 
organic  matter  is  much  retarded,  if  the  vessel  be  altogether  secluded 
from  it.  The  rapidity  with  which  the  small  Entomostracous  Crustacea 
(Water-Fleas,  &c.)  of  our  pools,  undergo  their  transformations,  has  been 
found  to  be  much  influenced  by  the  amount  of  light  to  which  they  are 
exposed.  And  it  has  been  ascertained  that,  if  equal  numbers  of  Silk- 
worm's eggs  be  preserved  in  a  dark  room,  and  exposed  to  common  day- 
light, a  much  larger  proportion  of  larvae  are  hatched  from  the  latter 
than  from  the  former.  The  most  striking  proof  of  the  influence  of  Light 
on  Animal  development,  however,  is  afi'orded  by  the  experiments  of  Dr. 
Edwards.  He  has  shown  that  if  Tadpoles  be  nourished  with  proper 
food,  and  be  exposed  to  the  constantly  renewed  contact  of  water  (so 
that  their  respiration  may  be  freely  carried  on,  whilst  they  remain  in 
their  fish-like  condition),  but  be  entirely  deprived  of  light,  their  growth 
continues,  but  their  metamorphosis  into  the  condition  of  air-breathing 
animals  is  arrested,  and  they  remain  in  the  condition  of  gigantic  tad- 
poles. It  is  interesting  to  remark,  that  the  Proteus  anguineus,  an  ani- 
mal which  closely  corresponds  in  its  fully-developed  form  with  the 
transition  stage  between  the  Tadpole  and  the  Frog,  finds  a  congenial 
abode  in  the  dark  lakes  of  the  caverns  of  Styria  and  Carniola,  and  in 
the  underground  caverns  that  connect  them ;  thus  showing  its  adapta- 
tion to  a  condition,  which  keeps  down  to  the  same  standard  the  develop- 
ment of  an  animal,  that  is  empowered  under  other  circumstances  to  ad- 
vance beyond  it.  Numerous  facts,  collected  from  diff'erent  sources,  lead 
to  the  belief  that  the  healthy  development  of  the  Human  body,  and  the 
rapidity  of  its  recovery  from  disease,  are  greatly  influenced  by  the 
amount  of  light  to  which  it  has  been  exposed.  It  has  been  observed, 
on  the  one  hand,  that  a  remarkable  freedom  from  deformity  exists 
amongst  nations  who  wear  very  little  clothing ;  whilst,  on  the  other,  it 
appears  certain  that  an  unusual  tendency  to  deformity  is  to  be  found 
among  persons  brought  up  in  cellars  or  mines,  or  in  dark  and  narrow 
streets.  Part  of  this  difierence  is  doubtless  owing  to  the  relative  purity 
of  the  atmosphere  in  the  former  case,  and  the  want  of  ventilation  in  the 
latter ;  but  other  instances  might  be  quoted,  in  which  a  marked  variation 
presented  itself,  under  circumstances  otherwise  the  same.  Thus,  it  has 
been  stated  by  Sir  A.  Wylie  (who  was  long  at  the  head  of  the  medical 
stafi"  in  the  Russian  army),  that  the  cases  of  disease  on  the  dark  side  of 
an  extensive  barrack  at  St.  Petersburgh,  have  been  uniformly,  for  many 


INFLUENCE  OF  HEAT  ON  PLANTS.  71 

years,  in  the  proportion  of  three  to  one,  to  those  on  the  side  exposed  to 
strong  light.  And  in  one  of  the  London  Hospitals,  with  a  long  range 
of  frontage  looking  nearly  due  north  and  south,  it  has  been  observed 
that  residence  in  the  south  wards  is  much  more  conducive  to  the  welfare 
of  the  patients  than  in  those  on  the  north  side  of  the  building. 

96.  These  facts  being  kept  in  view,  it  is  easy  to  perceive  that  there 
must  be  differences  among  the  various  species  of  Animals,  as  among 
those  of  Plants,  in  regard  to  the  degree  of  light  which  is  congenial  to 
them.  Among  the  lowest  tribes,  in  which  no  special  organs  of  vision 
exist,  there  is  evidently  a  susceptibility  to  the  influence  of  light,  which 
appears  scarcely  to  deserve  the  name  of  sensibility,  but  which  seems 
rather  analogous  to  that  which  is  manifested  by  Plants  ;  thus  among 
those  Polypes  which  are  not  fixed  to  particular  spots,  and  amongst  Ani- 
malcules, there  are  some  species  which  seek  the  light,  and  others  which 
shun  it.  And  it  appears  from  various  observations  upon  the  depths  at 
which  marine  animals  are  found,  especially  from  the  extensive  series  of 
facts  collected  by  Prof.  E.  Forbes,*  that  there  are  a  series  of  zones,  so 
to  speak,  to  be  met  with  in  descending  from  the  surface  towards  the 
bottom  of  the  ocean,  each  of  which  is  characterized  by  certain  species 
of  animals  peculiar  to  itself,  whilst  other  species  have  a  range  through 
two  or  more  of  the  zones ; — the  extent  of  the  range  of  depth,  in  each 
species,  bearing  a  close  correspondence  with  the  extent  of  its  geographical 
distribution.  Now  there  can  be  no  doubt,  that  the  restriction  of  par- 
ticular species  to  particular  zones  is  due  in  great  part  to  the  degree  of 
pressure  of  the  surrounding  medium ;  but  there  can  be  as  little  doubt, 
that  the  variation  in  the  degree  of  Light  also  exerts  a  most  important 
influence,  the  solar  rays  in  their  passage  through  sea  water  being  subject 
to  a  loss  of  one  half  for  every  seventeen  feet.  From  the  results  of  Prof. 
Forbes's  researches,  it  appears  that  no  species  of  Invertebrated  animals 
habitually  live  at  a  greater  depth  than  300  fathoms  ;  and  although  Fishes 
have  been  captured  at  a  depth  of  from  500  to  600  fathoms,  it  is  probable 
that  they  had  strayed  from  their  usual  abodes. 

2.   Of  Heat,  as  a  Condition  of  Vital  Activity. 

97.  The  most  perfectly-organized  body,  supplied  with  all  the  other 
conditions  requisite  for  its  activity,  must  remain  completely  inert,  if  it 
do  not  receive  a  sufficient  amount  of  Heat.  The  influence  which  this 
agent  exerts  upon  living  beings,  is  far  more  remarkable  than  its  effects 
upon  inorganic  matter ;  although  the  latter  are  usually  more  obvious. 
We  are  all  familiar  with  its  power  of  producing  expansion, — with  the 
liquefaction  which  is  the  consequence  of  its  application  to  solids, — with 
the  evaporation  which  it  occasions  in  liquids, — and  with  the  enormous 
repulsive  force  which  it  generates  among  the  particles  of  vapours ;  but 
it  is  not  until  we  look  deeper  than  the  surface,  that  we  perceive  how 
immediate  is  the  dependence  of  every  action  of  Life  upon  this  myste- 
rious agent.  The  temporary  or  permanent  loss  of  vitality,  in  parts  of 
the  body  subjected  to  extreme  cold,  is  a  "  glaring  instance"  of  the  effect 

*  Report  on  the  Invertebrata  of  the  ^gean  Sea,  in  Transactions  of  British  Associa- 
tion, 1843. 


72  EXTERNAL  CONDITIONS   OF  VITAL  ACTIVITY. 

of  its  withdrawal.  This  change,  however,  is  not  immediate.  Its  first 
step  is  a  mere  depression  of  the  vitality  of  the  part,  involving  a  partial 
stagnation  of  the  capillary  circulation,  diminution  of  sensibility,  and 
want  of  muscular  power.  But  the  continued  action  of  cold  on  the  sur- 
face, not  compensated  by  a  sufficient  generation  of  heat  within,  causes 
the  circulation  of  the  part  to  be  completely  suspended,  its  small  vessels 
contract  so  that  they  become  almost  emptied  of  blood,  its  sensibility  and 
power  of  movement  are  destroyed, — in  a  word,  its  vital  activity  is  com- 
pletely suspended.  In  such  a  state,  a  timely  but  cautious  application 
of  warmth  may  produce  the  gradual  renewal  of  the  circulation,  and  the 
restoration  of  the  other  properties  of  the  part,  which  are  dependent  upon 
that  function ;  but  any  abrupt  change  would  complete  the  mischief  which 
the  cold  has  begun ;  and  would  altogether  destroy,  by  the  violence  of 
the  reaction,  the  vitality  which  was  only  suspended,  causing  the  actual 
death  of  the  part.  Hence,  when  the  extremities  are  frost-bitten,  nothing 
can  be  more  injurious  than  to  bring  them  near  a  fire ;  whilst  no  treat- 
ment has  been  found  so  safe  and  efiectual  as  the  rubbing  them  with  snow. 

98.  The  influence  of  Heat  upon  Vital  activity,  is  attested  on  a  larger 
scale,  by  the  striking  contrast  between  the  dreary  barrenness  of  Polar 
regions,  and  the  luxuriant  richness  of  Tropical  countries,  where  almost 
every  spot  to  which  moisture  is  supplied  teems  with  Animal  and  Vege- 
table life.  And  the  alternation  of  Winter  and  Summer  in  temperate 
climates,  may  be  almost  said  to  bring  under  our  own  view  the  opposite 
conditions  of  those  two  extreme  cases.  The  efi"ect  of  the  withdrawal  of 
Heat  is  most  obvious  in  the  Vegetable  kingdom  ;  since  all  its  operations 
are  dependent  upon  a  certain  supply  of  that  agent ;  and  in  no  case  are 
Plants  possessed  of  the  power  of  generating  that  supply  within  them- 
selves,— excepting  in  certain  organs  which  do  not  impart  it  to  the  rest 
of  the  structure.  When  the  temperature  of  the  air  falls  to  the  freezing- 
point,  therefore,  we  find  all  the  operations  of  the  Vegetable  economy 
undergoing  a  complete  suspension ;  yet  a  very  trifling  rise  will  produce 
a  renewal  of  them.  It  is  not  only  in  Evergreens,  that  the  vital  pro- 
cesses continue  to  be  performed  to  a  certain  extent  during  the  winter ; 
for  there  is  abundant  evidence  that,  even  in  the  trunk  and  branches  of 
trees  unclothed  with  leaves,  a  circulation  of  sap  takes  place,  whenever 
there  is  even  a  slight  return  of  warmth.  In  this  manner,  the  leaf-buds 
are  gradually  prepared  during  the  milder  days  of  winter,  so  as  to  be 
ready  to  start  forth  into  full  development,  with  the  returning  steady 
warmth  of  spring. 

99.  The  influence  of  Heat  upon  Vegetation  is  easily  made  apparent 
by  experiment ;  in  fact  experimental  illustrations  of  it,  on  a  large  scale, 
are  daily  in  progress.  For  the  Gardener,  by  artificial  warmth,  is  not 
only  enabled  to  rear  with  success  the  plants  of  tropical  climates,  whose 
constitution  would  not  bear  the  chilling  influence  of  our  winter ; — but 
he  can  also,  in  some  degree,  invert  the  order  of  the  seasons,  and  produce 
both  blossom  and  fruit  from  the  plants  of  our  own  country,  when  all 
around  seems  dead.  This  process  of  forcing,  however,  is  unfavourable 
to  the  health  and  prolonged  existence  of  the  plants  subjected  to  it; 
since  the  period  of  repose,  which  is  natural  to  them,  is  interrupted ;  and 
they  are  caused,  as  it  were,  to  live  too  fast.     The  same  result  occurs, 


i 


INFLUENCE  OP  HEAT  ON  PLANTS.  78 

when  a  plant  or  tree  of  temperate  climates  is  transported  to  the  tropics. 
Within  a  very  short  period  after  one  crop  of  leaves  has  fallen  off,  a  new 
one  makes  its  appearance.  This  goes  through  all  its  changes  of  develop- 
ment and  decay  more  rapidly  than  it  would  do  in  its  native  clime ;  and 
in  its  turn  falls  oflf,  and  is  speedily  succeeded  by  another.  Hence  the 
fruit-trees  of  this  country,  transported  to  the  East  or  West  Indies,  bear 
abundant  crops  of  leaves, — three,  perhaps,  in  one  year,  or  five  in  two" 
years, — but  little  or  no  fruit ;  and  the  period  of  their  existence  is  much 
shortened. 

100.  As  Plants  are  almost  wholly  dependent  upon  the  temperature  of 
the  surrounding  medium  for  the  supply  of  Heat  necessary  for  their 
gfowth,  many  regions  must  have  been  devoid  of  Vegetable  life  altogether ; 
if  there  were  not  a  remarkable  adaptation,  in  the  wants  of  difierent 
species,  to  the  various  degrees  of  temperature  of  the  habitations  prepared 
for  them.  Thus  we  see  the  Cacti  and  Euphorbiae  attaching  themselves 
to  the  surface  of  the  most  arid  rocks  of  tropical  regions,  luxuriating,  as 
it  would  seem,  in  the  full  glare  of  the  vertical  sun,  and  laying  up  a  store 
of  moisture  from  the  periodical  rains,  of  which  even  a  long-continued 
drought  is  not  sufficient  to  deprive  them.  The  Orchideous  tribe,  on  the 
other  hand,  whose  greatest  development  occurs  in  the  same  zone,  find 
their  congenial  habitation  in  the  depths  of  the  tangled  forests,  where, 
with  scarcely  an  inferior  amount  of  heat,  they  have  the  advantage  of  a 
moister  atmosphere,  caused  by  the  exhalations  of  the  trees  on  which  they 
cling.  The  majestic  Tree-Fern,  again,  reaches  its  full  development  in 
insular  situations ;  where,  with  a  moist  atmosphere,  it  can  secure  a 
greater  equability  of  temperature  than  is  to  be  met  with  in  the  interior 
of  the  vast  tropical  continents.  None  of  these  races  can  develope 
themselves  elsewhere  to  their  full  extent  at  least,  unless  their  natural 
conditions  of  growth  are  imitated  as  far  as  possible ;  and  in  proportion 
as  this  imitation  can  be  made  complete,  in  that  proportion  may  the  plant 
of  the  tropics  be  successfully  reared  in  temperate  regions. 

101.  There  are  some  examples  of  the  adaptation  of  particular  forms 
of  Vegetable  life  to  extremes  of  temperature,  which  are  interesting  as 
showing  the  extent  to  which  this  adaptation  may  be  carried.  In  hot 
springs  near  a  river  of  Louisiana,  of  the  temperature  of  from  122°  to 
145°,  there  have  been  seen  to  grow,  not  merely  Confervas  and  herbaceous 
plants,  but  shrubs  and  trees ;  and  a  hot-spring  in  the  Manilla  Islands, 
which  raises  the  thermometer  to  187°,  has  plants  flourishing  in  it,  and 
on  its  borders.  A  species  of  Qhara  has  been  found  growing  and  repro- 
ducing itself  in  one  of  the  hot-springs  of  Iceland,  which  boiled  an  egg  in 
four  minutes ;  various  Confervse,  &c.,  have  been  observed  in  the  boiling- 
springs  of  Arabia  and  the  Cape  of  Good  Hope  ;  and  at  the  island  of  New 
Amsterdam,  there  is  a  mud-spring,  which,  though  hotter  than  boiling- 
water,  gives  birth  to  a  species  of  Liverwort.  On  the  other  hand,  there 
are  some  forms  of  Vegetation,  which  seem  to  luxuriate  in  degrees  of  cold, 
that  are  fatal  to  most  others.  Thus  the  Lichen,  which  serves  as  the 
winter  food  of  the  Rein-deer,  spreads  itself  over  the  ground  whilst  thickly 
covered  with  snow ;  and  the  beautiful  little  Frotoeoecus  nivalis,  or  Red 
Snow,  reddens  extensive  tracts  in  the  Arctic  regions,  where  the  perpetual 


74  EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

frost  of  the  surface  scarcely  yields  to  the  influence  of  the  solar  rays  at 
Midsummer. 

102.  It  is,  for  the  most  part,  among  the  Cryptogamic  tribes, — the 
Ferns,  Mosses,  Liverworts,  Fungi,  and  Lichens, — that  the  greatest 
power  of  growing  under  a  low  temperature  exists ;  and  we  accordingly 
find  that  the  proportion  of  these  to  the  Phanerogamia,  or  Flowering 
Plants,  increases  as  we  proceed  from  the  Equator  towards  the  Poles. 
It  has  been  estimated  by  Humboldt,  that,  in  Tropical  regions,  the  num- 
ber of  species  of  Cryptogamia  is  only  about  one-tenth  that  of  the  Flow- 
ering Plants ;  in  the  part  of  the  Temperate  zone  which  lies  between 
lat.  45°  and  52°,  the  proportion  rises  to  one-half ;  and  the  relative 
amount  gradually  increases  as  we  proceed  towards  the  Poles,  until,  be- 
tween lat.  67°  and  70°,  the  number  of  species  of  Cryptogamia  equals 
that  of  the  Phanerogamia.  Among  the  Flowering  Plants,  moreover, 
the  greatest  endurance  of  cold  is  to  be  found  in  those,  which  approach 
most  nearly  to  the  Cryptogamia  in  the  low  degree  of  their  development ; 
thus  the  Glumaceous  group  of  Endogens,  including  the  Grasses,  Rushes, 
and  Sedges,  which  forms  about  one-eleventh  of  the  whole  amount  of 
Phanerogamic  vegetation  in  the  Tropics,  constitutes  one-fourth  of  it  in 
the  Temperate  regions,  and  one-third  in  the  Polar ;  and  the  ratio  of  the 
Gymnospermic  group  of  Exogens,  which  chiefly  consists  of  the  Pine 
and  Fir  tribe,  increases  in  like  manner.  Still  the  influence  of  a  high 
temperature  is  evident  even  upon  the  Cryptogamia  and  their  allies  ;  for 
it  is  only  under  the  influence  of  the  light  and  warmth  of  tropical  climes, 
that  the  Ferns, — the  highest  among  the  former, — can  develope  a  woody 
stem,  and  assume  the  character  of  trees ;  and  it  is  only  there  that  the 
tall  Sugar-Canes,  and  the  gigantic  Bamboos,  which  are  but  Grasses  on 
a  large  scale,  can  flourish. 

103.  It  appears,  then,  that  to  every  species  of  Vegetable  there  is  a 
temperature  which  is  most  congenial,  from  its  producing  the  most 
favourable  influence  on  its  general  vital  actions.  There  is  a  considera- 
ble diff*erence  between  the  power  of  growing  and  of  flourishing,  at  a 
given  temperature.  We  may  lower  the  heat  of  a  plant  to  such  a  degree, 
as  to  allow  it  to  continue  to  live ;  yet  its  condition  will  be  unhealthy. 
It  absorbs  food  from  the  earth  and  air,  but  cannot  assimilate  and  con- 

•  vert  it.  Its  tissue  grows,  but  becomes  distended  with  water,  instead  of 
being  rendered  firm  by  solid  deposits.  The  usual  secretions  are  not 
formed ;  flavour,  sweetness,  and  nutritive  matter,  are  each  diminished ; 
and  the  power  of  flowering  and  producing  fruit  is  lost.  We  see  a  diffe- 
rence in  the  amount  of  heat  required  for  the  vegetating  processes,  even 
in  the  various  species  indigenous  to  our  own  climate ;  thus  the  common 
Chickweed  and  Groundsel  evidently  grow  readily  at  a  temperature  but 
little  above  the  freezing  point,  whilst  the  Nettles,  Mallows,  and  other 
weeds  around  them  remain  torpid.  But  the  difi*erence  is  much  more 
strongly  marked  in  the  vegetation  of  diff'erent  climates;  showing  an 
evident  adaptation  of  the  tribes  indigenous  to  each,  to  that  range  of 
temperature  which  they  will  there  experience.  Instead  of  being  scantily 
supplied  with  such  of  the  tropical  plants  as  could  support  a  stunted  and 
precarious  life  in  ungenial  climates,  the  temperate  regions  are  stocked 
with  a  multitude  of  vegetables  which  appear  to  be  constructed  expressly 


INFLUENCE  OF  HEAT  ON  PLANTS.  75 

for  them ;  inasmucli  as  thece  species  can  no  more  flourish  at  the  Equa- 
tor, than  the  equatorial  species  can  in  these  Temperate  regions.  And 
such  new  supplies,  adapted  to  new  conditions,  recur  perpetually  as  we 
advance  towards  the  apparently  frozen  and  untenantable  regions  in  the 
neighbourhood  of  the  Pole.  Every  zone  has  its  peculiar  vegetables ; 
and  while  we  miss  some,  we  find  others  making  their  appearance,  as  if 
to  replace  those  which  are  absent. 

104.  Thus  in  the  countries  lying  near  the  Equator,  the  vegetation 
consists  in  great  part  of  dense  forests  of  leafy  evergreen  trees.  Palms, 
Bamboos,  and  Tree-Ferns,  bound  together  by  clustering  Orchidse  and 
strong  creepers  of  various  kinds.  There  are  no  verdant  meadows,  such 
as  form  the  chief  beauty  of  our  temperate  regions  ;  and  the  lower  orders 
of  Vegetation  are  extremely  rare.  It  is  only  in  this  torrid  zone  that 
Dates,  Coffee,  Cocoa,  Bread-fruit,  Bananas,  Cinnamon,  Cloves,  Nut- 
megs, Pepper,  Myrrh,  Indigo,  Ebony,  Logwood,  Teak,  Sandal-wood, 
and  many  others  of  the  vegetable  products  most  highly  valued  for  their 
flavour,  their  odour,  their  colour,  or  their  density,  come  to  full  perfec- 
tion. As  we  recede  from  the  Equator,  we  find  the  leafy  evergreens 
giving  place  to  trees  with  deciduous  leaves ;  rich  meadows  appear, 
abounding  with  tender  herbs ;  the  Orchidese  no  longer  find  in  the  atmo- 
sphere, and  on  the  surface  of  the  trees  over  which  they  cluster,  a  suffi- 
ciency of  moisture  for  their  support,  and  the  parasitic  species  are  re- 
placed by  others  which  grow  from  fleshy  roots  implanted  in  the  soil ; 
but  aged  trunks  are  now  clothed  with  Mosses :  decayed  vegetables  are 
covered  with  parasitical  Fungi ;  and  the  waters  abound  with  Confervae. 
In  the  warmer  parts  of  the  temperate  regions,  the  Apricot,  Citron, 
Orange,  Lemon,  Peach,  Fig,  Vine,  Olive,  and  Pomegranate,  the  Myrtle, 
Cedar,  Cypress,  and  Dwarf  Palm,  find  their  congenial  abode.  These 
give  place,  as  we  pass  northwards,  to  the  Apple,  the  Plum,  and  the 
Cherry,  the  Chestnut,  the  Oak,  the  Elm,  and  the  Beech.  Going  fur- 
ther still,  we  find  that  the  fruit  trees  are  unable  to  flourish,  but  the  tim- 
ber-trees maintain  their  ground.  Where  these  last  fail,  we  meet  with 
extensive  forests  of  the  various  species  of  Firs  ;  the  Dwarf  Birches  and 
Willows  replace  the  larger  species  of  the  same  kind ;  and  even  near  or 
within  the  Arctic  circle  we  find  large  flowers  of  great  beauty, — the 
Mezereon,  the  yellow  and  white  Water-Lily,  and  the  Globe-flower. 
Where  none  of  these  can  flourish,  where  trees  wholly  disappear,  and 
scarcely  any  flowering-plants  are  to  be  met  with,  an  humbler  Cryptoga- 
mic  vegetation  still  raises  its  head,  in  proof  that  no  part  of  the  Globe  is 
altogeth.er  unfit  for  the  residence  of  living  beings,  and  that  the  empire 
of  Flora  has  no  limit. 

105.  But  distance  from  the  Equator  is  by  no  means  the  only  element 
in  the  determination  of  the  mean  temperature  of  a  particular  spot,  and 
of  the  vegetation  which  is  congenial  to  it.  Its  height  above  the  level 
of  the  sea  is  equally  important ;  for  this  produces  a  variation  in  the 
amount  of  heat  derived  from  the  Sun,  at  least  as  great  as  that  occa- 
sioned by  difference  of  latitude.  Thus  it  is  not  alone  on  the  summits 
of  Hecla,  Mount  Blanc,  and  other  mountains  of  Arctic  or  temperate 
regions,  that  we  find  a  coating  of  perpetual  snow ;  we  find  a  similar 
covering  on  the  lofty  summits  of  the  Himalayan  chain,  which  extends 


76  EXTERNAL  CONDITIONS   OP  VITAL  ACTIVITY. 

to  within  a  few  degrees  of  the  Tropic  of  Cancer ;  and  eVen  on  the  higher 
peaks  of  that  part  of  the  ridge  of  the  Andes,  which  lies  immediately 
beneath  the  Equator.  The  height  of  the  snow-line  beneath  the  Equator 
is  between  15,000  and  16,000  feet  above  the  le(Vel  of  the  sea ;  on  the 
south  side  of  the  Himalayan  ridge  it  is  about  15,500  feet,-  but  on  the 
north  side  it  rises  to  18,500  feet ;  and  in  the  Swiss  Alps  it  is  about 
8000  feet.  Its  position  is  very  much  affected,  however,  by  local  cir- 
cumstances, such  as  the  neighbourhood  of  a  large  expanse  of  land  or  of 
sea;  hence  the  small  quantity  of  land  in  the  Southern  Hemisphere, 
renders  its  climate  generally  so  much  colder  than  that  of  the  Northern, 
that  in  Sandwich  Land  (which  is  lat.  59°  S.,  or  in  the  same  parallel  as 
the  north  of  Scotland)  the  whole  country,  from  the  summits  of  the 
mountains  down  to  the  very  brink  of  the  sea-cliffs,  is  covered  many 
fathoms  thick  with  everlasting  snow ;  and  in  the  Island  of  Georgia 
(which  is  in  lat.  54°  S.,  or  in  the  same  parallel  as  Yorkshire),  the  limit  of 
perpetual  snow  descends  to  the  level  of  the  ocean,  the  partial  melting 
in  summer  only  disclosing  a  few  rocks,  scantily  covered  with  moss  and 
tufts  of  grass.  Yet  the  highest  mountains  of  Scotland,  which  ascend 
to  an  elevation  of  nearly  5000  feet,  and  are  four  degrees  more  distant 
from  the  equator,  do  not  attain  the  limit  of  perpetual  snow ;  this  is 
reached,  however,  by  mountains  in  Norway,  at  no  greater  elevation. 

106.  If,  then,  Temperature  exert  such  an  influence  on  Vegetation  as 
has  been  stated,  we  ought  to  find  on  the  sides  of  lofty  mountains  in 
tropical  regions,  the  same  progressive  alterations  in  the  characters  of 
the  Plants  that  cover  them,  as  we  encounter  in  journeying  from  the 
equatorial  towards  the  polar  regions.  This  is  actually  the  case.  The 
proportion  of  Cryptogamia  to  Flowering  Plants,  for  example,  is  no  more 
than  one-fifteenth  on  the  plains  of  the  Equatorial  region  ;  whilst  it  is  as 
much  as  one-fifth  on  the  mountains.  In  ascending  the  Peak  of  Tene- 
riffe,  Humboldt  remarked  as  many  as  five  distinct  zones,  which  were 
respectively  marked  by  the  products  which  characterize  different 
climates.  Thus  at  the  base,  the  vegetation  is  altogether  tropical; 
the  Date-Palm,  Plantain,  Sugar-Cane,  Banyan,  the  succulent  Euphor- 
bia, the  Dracaena,  and  other  trees  and  plants  of  the  torrid  zone  there 
flourish.  A  little  higher  grow  the  Olive,  the  Vine,  and  other  fruit- 
trees  of  Southern  Europe ;  there  Wheat  flourishes ;  and  there  the 
ground  is  covered  with  grassy  herbage.  Above  this  is  the  woody 
region,  in  which  are  found  the  Oak,  Laurel,  Arbutus,  and  other  beau- 
ful  hardy  evergreens.  Next  above  is  the  region  of  Pines  ;  characterized 
by  a  vast  forest  of  trees  resembling  the  Scottish  Fir,  intermixed  with 
Juniper.  This  gives  place  to  a  tract  remarkable  for  the  abundance  of 
Broom ;  and  at  last  the  scenery  is  terminated  by  Scrofularia,  Viola,  a 
few  Grasses,  and  Cryptogamic  plants,  which  extend  to  the  borders  of 
the  perpetual  snow  that  caps  the  summit  of  the  mountain. 

107.  The  effects  of  Temperature  on  Vegetation  are  not  only  seen  in 
its  influence  upon  the  Geographical  distribution  of  Plants,  that  is,  in 
the  limitation  of  particular  species  to  particular  climates ;  for  they  are 
shown,  perhaps  even  more  remarkably,  in  the  variation  in  the  size  of 
individuals  of  the  same  species  ;  when  that  species  possesses  the  power 
of  adapting  itself  to  widely  different  conditions,  which  is  the  case  with 


INFLUENCE  OF  HEAT  ON  PLANTS.  77 

some.  Thus  the  Oerasus  Virginiana  grows  in  the  Southern  States  of 
North  America  as  a  noble  tree,  attaining  one  hundred  feet  in  height ; 
in  the  sandy  plains  of  the  Saskatchawan,  it  does  not  exceed  twenty  feet; 
and  at  its  northern  limit,  the  Great  Slave  Lake,  in  lat.  62°,  it  is  re- 
duced to  a  shrub  of  five  feet.  Another  curious  effect  of  heat  is  shown 
in  its  influence  on  the  sexes  of  certain  Monoecious  flowers ;  thus  Mr. 
Knight  mentions  that  Cucumber  and  Melon  plants  will  produce  none 
but  male  or  staminiferous  flowers,  if  their  vegetation  be  accelerated  by 
heat ;  and  all  female  or  pistilliferous,  if  its  progress  be  retarded  by  cold. 

108.  The  injurious  influence  of  excessive  Heat  can  be,  to  a  certain 
extent,  resisted  by  Plants,  through  the  cooling  process  kept  up  by  the 
continual  evaporation  of  moisture  from  their  surface.  But  the  power 
of  maintaining  this  cooling  process  entirely  depends  upon  the  supply  of 
fluid,  with  which  the  plant  is  furnished.  If  the  supply  be  adequate  to 
the  demand,  the  efiect  of  heat  will  be  to  stimulate  all  the  vital  opera- 
tions of  the  plant,  and  to  cause  them  to  be  performed  with  increased 
energy ;  though,  as  we  have  already  seen,  this  energy  may  be  such  as 
to  occasion  a  premature  exhaustion  in  its  powers,  by  the  excessive  luxu- 
riance which  it  occasions.  But  if  the  supply  of  water  be  deficient,  the 
plant  is  burnt  up  by  the  continuance  of  heat  in  a  dry  atmosphere ;  and 
it  either  withers  and  dies,  or  its  tissues  become  dense  and  contracted, 
without  losing  their  vitality.  Thus  it  has  been  remarked,  that  shrubs 
LHowing  among  the  sandy  deserts  of  the  East,  have  as  stunted  an  ap- 
{)earance  as  those  attempting  to  vegetate  in  the  Arctic  regions ;  their 
leaves  being  converted  into  prickles,  and  their  leaf-buds  prolonged  into 
:horns  instead  of  branches. — The  influence  of  excessive  heat  in  destroy- 
ing life,  can  sometimes  be  traced  through  the  direct  physical  changes 
which  it  occasions  in  the  vegetable  tissues.  Thus  it  has  been  ascer- 
tained that  grains  of  corn  will  vegetate,  after  exposure  to  water  or 
vapour  possessing  a  considerable  degree  of  heat ;  provided  that  heat  do 
not  amount  to  144°  in  the  case  of  water,  and  167°  in  that  of  vapour. 
At  these  temperatures,  the  structure  of  the  seed  undergoes  a  disorga- 
nizing change,  by  the  rupture  of  the  vesicles  of  starch  which  form  a 
large  part  of  it ;  and  the  loss  of  its  power  of  germinating  is  therefore 
readily  accounted  for.  The  highest  temperature  which  the  soil  usually 
possesses  in  tropical  climates,  is  about  126°,  though  Humboldt  has  once 
observed  the  thermometer  rise  to  140°.  Seeds  imbedded  in  such  a  soil, 
tlierefore,  may  not  lose  their  vitality,  although  they  will  not  germinate 
ill  such  temperatures.  The  temperature  most  favourable  to  germination 
probably  varies  in  diff"erent  species,  and  is  one  of  the  conditions  that 
produces  their  adaptation  to  difi'erent  climates.  Thus  it  appears  that 
Covn  will  not  germinate  in  water  at  a  higher  temperature  than  95°, 
wliilst  Maize  will  germinate  in  water  at  113° ;  and,  as  is  well  known, 
Maize  will  flourish  in  countries  in  which  Corn  cannot  be  grown. 

109.  We  must  not  confound  the  power  which  Plants  possess  of  vege- 
Hating,  or  exhibiting  vital  activity,  under  widely-difierent  degrees  of 
temperature,  with  the  power  of  retaining  their  vitality  in  a  dormant 
.condition,  which  many  of  them  possess  in  a  very  remarkable  degree. 

I  When  the  external  temperature  is  much  below  the  freezing-point,  it  is 
impossible  that  any  vegetating  processes  can  go  on;  since  the  Plant 


78  EXTERNAL   CONDITIONS   OF  VITAL   ACTIVITY. 

does  not  possess  the  power  of  generating  heat  within  itself.  Now  such 
a  complete  cessation  of  activity  is  quite  compatible,  in  many  instances, 
with  the  preservation  of  the  organized  structure  in  a  condition  perfectly 
unchanged,  and,  in  consequence,  with  the  continuance  of  its  peculiar 
properties  ;  so  that  these  properties  may  be  again  called  into  operation, 
when  the  temperature  shall  have  risen.  But  in  other  cases,  the  plant 
may  be  hilled  by  the  intensity  of  the  cold ;  that  is,  the  return  of  warmth 
will  not  excite  it  to  activity.  We  have  occasion  to  notice,  in  every 
severe  winter,  the  difference  in  this  respect  amongst  the  plants  which 
are  cultivated  in  our  own  climate ;  some  of  them  being  killed  by  a  hard 
frost,  the  effects  of  which  are  resisted  by  others,  even  though  their  situa- 
tion be  more  exposed.  In  general  it  will  be  found,  that  the  cold  acts 
most  powerfully  (as  might  be  expected)  upon  plants  which  are  not  indi- 
genous to  our  country,  but  which  have  been  introduced  and  naturalized 
from  some  warmer  regions.  But  it  is  worthy  of  note,  amongst  other  pe- 
culiarities in  the  relation  of  Heat  and  Vegetation,  that  many  plants  are 
readily  killed  by  a  low  temperature,  which  yet  flourish  well  under  a  very 
moderate  amount  of  warmth;  so  that  they  will  grow  in  situations  where 
the  mean  temperature  of  the  year  is  low  and  the  summers  cool,  provided 
the  winters  are  not  severe ;  whilst  they  cannot  be  preserved  without 
special  protection,  in  situations  where  the  winters  are  colder,  even  though 
the  summers  should  be  much  hotter,  and  the  mean  temperature  of  the 
whole  year  should  be  considerably  higher.  Thus  there  are  shrubs  grow- 
ing in  the  Botanic  Garden  of  Edinburgh,  which  cannot  be  safely  left  in 
the  open  air  in  the  neighbourhood  of  London,  and  which  would  be  most 
certainly  killed  by  the  winter-cold  of  Central  France. 

110.  It  does  not  admit  of  doubt,  that  the  destructive  influence  of  a 
very  low  temperature  upon  the  Vitality  of  Plants,  is  immediately  exerted 
through  its  chemical  and  physical  effects  upon  the  tissues  and  their  con- 
tents. Thus  it  will  produce  congelation  of  their  fluids ;  and  the  expan- 
sion which  takes  place  in  freezing  will  injure  the  walls  of  the  containing 
cells, — distending,  lacerating,  or  even  bursting  them.  The  same  cause 
will  probably  occasion  the  expulsion  of  air  from  some  parts  which  ought 
to  contain  it ;  and  the  introduction  of  it  into  other  parts  which  ought  to 
be  filled  with  fluid.  And  a  separation  will  take  place,  in  the  act  of 
freezing,  between  the  constituent  parts  of  the  vegetable  juices ;  which 
will  render  them  unfit  for  discharging  their  functions,  when  returning 
warmth  would  otherwise  call  them  into  activity.  Hence  we  are  enabled 
in  some  degree  to  account  for  the  differences  in  the  power  of  resisting 
cold,  which  the  various  species  of  Plants,  and  even  the  various  parts  of 
the  same  individual,  are  found  to  possess.  For,  other  things  being 
equal,  the  power  of  each  plant,  and  of  each  part  of  a  plant,  to  resist  a 
low  temperature,  will  be  in  the  inverse  ratio  of  the  quantity  of  water 
contained  in  the  tissue ;  thus  a  succulent  herbaceous  plant  suffers  more 
than  one  with  a  hard  woody  stem  and  dense  secretions ;  and  young 
shoots  are  destroyed  by  a  degree  of  cold,  which  does  not  affect  old  shoots 
and  branches  of  the  same  shrub  or  tree.  Again,  the  viscidity  of  the 
fluids  of  some  plants  is  an  obstacle  to  their  congelation,  and  therefore 
enables  them  to  resist  cold ;  thus  it  is,  that  the  resinous  Pines  are,  of 
all  trees,  those  which  can  endure  the  lowest  temperature.     The  dimen- 


4 


INFLUENCE  OF  HEAT  ON  ANIMALS.  79 


sions  of  the  cells,  too,  of  which  the  tissue  is  composed,  appear  to  have 
an  influence ;  the  liability  to  freeze  being  diminished  by  a  very  minute 
subdivision  of  the  fluids.  And  when  the  roots  are  implanted  deep  in 
the  soil,  where  the  temperature  does  not  fall  by  many  degrees  so  low  as 
that  of  the  surface,  the  fluidity  of  the  sap  may  be  maintained,  in  spite 
of  an  extremely  cold  state  of  the  atmosphere. 

111.  It  is  in  Cryptogamic  plants,  that  the  greatest  power  of  sustain- 
ing Cold  exists;  as  might  be  inferred  from  what  has  been  already  stated 
in  regard  to  their  geographical  distribution.  The  little  Fungus  {Torula 
Cerevisice)  which  is  one  of  the  principal  constituents  of  Yeast,  does  not 
lose  its  vitality  by  exposure  to  a  temperature  of  76°  below  zero  ;  though 
it  requires  a  somewhat  elevated  temperature  for  its  active  growth.  It 
Avould  appear  that  Seeds  are  enabled  to  sustain  a  degree  of  cold,  without 
the  loss  of  their  vitality,  which  would  be  fatal  to  growing  plants  of  the 
same  species ;  thus  grains  of  corn,  of  various  kinds,  will  germinate  after 
being  exposed  for  a  quarter  of  an  hour  to  a  temperature  equal  to  that 
of  frozen  mercury.  It  is  not  difiicult  to  account  for  this,  when  the  close- 
ness of  their  texture,  and  the  small  quantity  of  fluid  which  it  includes, 
are  kept  in  view.  The  act  of  Germination,  however,  will  only  take  place 
under  a  rather  elevated  temperature ;  and  we  find  in  the  Chemical 
changes  which  it  involves,  a  provision  for  maintaining  this,  when  the 
process  has  once  commenced. 

112.  The  influence  of  Heat  upon  the  vital  activity  of  Animals,  is  quite 
as  strongly  marked  as  we  have  seen  it  to  be  in  the  case  of  Plants ;  but 
the  mode  in  which  it  is  exerted  is  in  many  instances  very  difi'erent.  In 
those  animals  which  are  endowed  with  great  energy  of  muscular  move- 
ment, and  in  which,  for  the  maintenance  of  that  energy,  the  nutritive 
functions  are  kept  in  constant  activity,  we  find  that  a  provision  exists 
for  the  development  of  heat  from  within,  so  as  to  keep  the  temperature 
of  the  body  at  a  certain  uniform  standard,  whatever  may  be  the  climate 
in  which  they  live.  Their  energy  and  activity  are,  in  fact,  so  dependent 
upon  the  steady  maintenance  of  a  high  temperature  in  their  bodies,  that, 
if  this  be  not  kept  up  nearly  to  its  regular  standard,  a  diminution  or 
even  a  complete  cessation  of  vital  action  takes  place,  and  even  a  total 
loss  of  vitality  may  result.  In  these  warm-blooded  animals,  as  they  are 
termed,  we  do  not  so  evidently  trace  the  eff'ects  of  Heat,  because  they 
are  constantly  being  exerted,  and  because  external  changes  have  but 
little  influence  upon  them,  unless  these  changes  are  of  an  extreme  kind. 
But  if  those  internal  operations,  on  which  the  maintenance  of  the  tem- 
perature is  dependent,  are  from  any  cause  retarded  or  suspended,  the 
efi'ect  is  immediately  visible,  in  the  depressed  activity  of  the  whole 
system.  In  the  class  of  Birds,  whose  muscular  energy,  and  whose  ge- 
neral functional  activity,  are  greater  and  more  constant  than  those  of 
any^other  animals,  the  temperature  is  pretty  steadily  maintained  at  from 
108°  to  112°;  and  we  shall  presently  see,  that  a  depression  of  the  heat 
of  the  body  to  about  80°  is  fatal.  Among  Mammalia,  the  temperature 
is  usually  maintained  at  from  98°  to  102°  ;  and  it  seems  that  in  them 
too  a.  depression  of  about  thirty  degrees  is  ordinarily  fatal. 

113.  In  the  difi'erent  tribes  of  Birds  and  Mammals,  we  find  a  very 
diversified  power  of  generating  heat ;  and  on  this  depends  their  adapta- 


80  EXTERNAL   CONDITIONS    OF   VITAL   ACTIVITY. 

tion  to  various  climates.  Where  the  usual  temperature  of  the  atmo- 
sphere is  but  little  below  the  normal  standard  of  the  body,  a  small 
amount  of  the  internal  calorifying  power  is  required ;  and  accordingly 
we  find  that  animals  which  naturally  inhabit  the  torrid  zone,  cannot  be 
kept  alive  elsewhere,  except,  like  the  Plants  of  the  same  regions,  by  ex- 
ternal heat.  On  the  other  hand,  the  animals  of  the  colder  temperate 
and  frigid  climes  are  endowed  with  a  much  greater  internal  calorifying 
power ;  and  their  covering  is  adapted  to  keep  in  the  heat  which  they 
generate.  Such  animals  (the  Polar  Bear  for  example)  cannot  be  kept 
in  health,  in  the  summer  of  our  own  country,  unless  means  are  taken 
for  their  refrigeration.  The  constitution  of  Man  seems  to  acquire,  by 
habitation  to  a  particular  set  of  conditions  through  successive  genera- 
tions, an  adaptation  to  differences  of  climate,  of  which  that  of  few  other 
animals  is  susceptible  ;  and  thus  we  find  different  races  of  human  beings 
inhabiting  countries,  which  are  subject  to  the  extremes  of  heat  and  cold. 
The  Hindoo  or  the  Negro,  suddenly  transported  to  Labrador  or  Siberia 
during  the  depth  of  winter,  would  probably  sink  in  the  course  of  a  few 
days,  from  want  of  power  to  generate  within  his  body  a  sufficient  amount 
of  heat,  to  resist  the  depressing  influence  of  the  external  cold ;  whilst 
on  the  other  hand,  the  Esquimaux,  suddenly  conveyed  to  the  hottest 
parts  of  India  or  Africa,  would  speedily  become  the  subject  of  disease, 
which  would  probably  terminate  his  life  in  a  short  time.  It  is  in  the 
inhabitant  of  temperate  climates,  who  is  naturally  exposed  during  the 
seasonal  changes  of  his  year,  to  a  wide  range  of  external  temperature, 
that  we  find  the  greatest  power  of  sustaining  the  extremes  of  either  cold 
or  heat ;  and  yet,  even  in  such,  the  continued  exposure  to  either  extreme, 
during  a  long  series  of  years,  will  so  much  influence  the  heat-producing 
power,  that  the  constitution  does  not  adapt  itself  readily  to  a  change  of 
conditions. 

114.  We  see,  then,  that  the  variations  observable  between  diff"erent 
races  in  this  respect,  are  only  exaggerations  (so  to  speak)  of  the  alter- 
nations which  an  individual  may  undergo  in  the  course  of  a  few  years ; 
and  it  is  easy  to  understand  how  such  an  adaptation  may  take  place  to 
an  increased  extent  in  successive  generations ; — this  being  the  regular 
law,  not  merely  in  regard  to  Man,  but  in  regard  to  other  animals  placed 
under  new  conditions,  to  which  they  have  a  certain,  but  limited,  power 
of  adapting  themselves.  Thus  we  find  that  a  European,  who  has  lived 
for  several  years  in  the  East  or  West  Indies,  suffers  considerably  from 
the  cold,  when  he  first  returns  to  winter  in  his  native  country ;  his  con- 
stitution having,  for  a  time,  lost  some  of  its  power  of  generating  heat. 
After  a  few  years'  residence,  however,  this  power  is  commonly  recovered 
to  its  original  extent,  unless  the  age  of  the  individual  be  too  far  ad- 
vanced ;  but  his  ^hildi^en,  if  they  have  been  not  only  born,  but  brought 
up,  in  the  hotter  climate,  experience  much  greater  difficulty  in  adapting 
themselves  to  the  colder  one. 

115.  The  conditions  on  which  the  power  of  maintaining  the  heat  of 
the  body,  in  despite  of  external  cold,  is  dependent,  will  become  the  sub- 
ject of  inquiry  hereafter  (chap.  x).  It  is  sufiicient  here  to  state,  that 
this  power  is  the-  result  of  numerous  Chemical  changes  going  on  within 
the  body ;  and  especially  of  a  process  analogous  to  combustion,  in  which 


I 


INFLUENCE  OF  HEAT  ON  ANIMALS.  81 


carbon  and  hydrogen,  taken  in  as  food,  are  made  to  unite  with  oxygen 
derived  from  the  atmosphere.  It  is  dependent,  therefore,  as  to  its 
amount,  upon  the  due  supply  of  the  combustible  material  on  the  one 
hand,  and  of  atmospheric  air  on  the  other.  If  the  former  be  not  fur- 
nished either  by  the  food,  or  by  the  fatty  matter  of  the  body  (which 
acts  as  a  kind  of  reserved  store  laid  up  against  the  time  of  need),  the_ 
heat  cannot  be  maintained ;  and  it  is  in  part  for  want  of  power  to  digest 
and  assimilate  a  sufficient  amount  of  this  kind  of  aliment,  that  animals 
of  warm  climates  cannot  maintain  their  temperature  in  colder  regions. 
On  the  other  hand,  if  the  supply  of  oxygen  be  deficient,  as  it  is  when 
the  respiration  is  impeded  by  diseased  conditions  of  various  kinds,  there 
is  a  similar  depression  of  temperature. 

116.  Now  if,  from  either  of  these  causes,  the  temperature  of  the  body 
of  a  Bird  or  Mammal  (except  in  the  case  of  the  hyhernating  species  of 
the  latter,  to  be  presently  noticed)  be  lowered  to  about  30°  below  its 
usual  standard,  not  only  is  there  a  cessation  of  vital  activity,  but  a  total 
loss  of  vital  properties  ;  in  other  words,  the  death  of  the  animal  is  a 
necessary  result.  This  occurrence  is  preceded  by  a  gradually-increasing 
torpidity ;  which  shows  the  depressing  influence  of  the  cooling  process 
upon  the  functions  in  general.  The  temperature  of  the  superficial  parts 
of  the  body  is,  of  course,  first  affected  ;  the  circulation  is  at  first  retarded, 
causing  lividity  of  the  skin ;  but,  as  the  temperature  becomes  lower,  the 
blood  is  almost  entirely  expelled  from  the  surface  by  the  contraction  of 
the  vessels,  and  paleness  succeeds.  At  the  same  time,  there  is  a  gradu- 
ally-increasing torpor  of  the  nervous  and  muscular  systems,  which  first 
manifests  itself  in  an  indisposition  to  exertion  of  any  kind,  and  then  in 
an  almost  irresistible  tendency  to  sleep.  At  the  same  time,  the  respi- 
ratory movements  become  slower,  from  the  want  of  the  stimulus  that 
should  be  given  by  the  warm  current  of  blood  to  the  Medulla  Oblongata, 
which  is  the  centre  of  those  movements ;  and  the  loss  of  heat  goes  on, 
therefore,  with  increased  rapidity,  until  the  temperature  of  the  whole 
body  is  so  depressed,  that  its  vitality  is  altogether  destroyed. 

IIT.  But  when  there  is  a  deficiency  of  the  proper  animal  heat,  the 
vital  activity  of  the  system  may  be  maintained  by  caloric  applied  by 
external  sources.  This  fact  is  of  high  scientific  value,  as  giving  the  most 
complete  demonstration  of  the  immediate  dependence  of  the  vital  func- 
tions of  warm-blooded  animals  upon  a  sustained  temperature  ;  and  its 
practical  importance  can  scarcely  be  overrated.  It  rests  chiefly  upon 
the  recent  experiments  of  Chossat,  who  had  in  view  to  determine  the 
circumstances  attending  death  by  Inanition,  or  starvation.  He  found 
that,  when  Pigeons  were  entirely  deprived  of  food  and  water,  their 
average  temperature  underwent  a  tolerably  regular  diminution  from  day 
to  day  ;  so  that,  after  several  days  (the  exact  number  varying  with  their 
previous  condition),  it  was  about  4i°  lower  than  at  first.  Up  to  this 
time,  it  seems  that  the  store  of  fat  laid  up  in  the  body  supplies  the 
requisite  material  for  the  combustive  process ;  so  that  no  very  injurious 
depression  of  temperature  occurs.  But,  as  soon  as  this  is  exhausted, 
the  temperature  falls  rapidly,  from  hour  to  hour ;  and  as  soon  as  the 
I  total  depression  has  reached  29^°  or  30°,  death  supervenes.  Yet  it  was 
found  by  M.  Chossat,  that  when  animals  thus  reduced  by  starvation, 


82  EXTERNAL    CONDITIONS    OF   VITAL   ACTIVITY. 

whose  death  seemed  impending  (death  actually  taking  place  in  many 
instances,  whilst  the  preliminary  processes  of  weighing,  the  application 
of  the  thermometer,  &c.,  were  being  performed),  were  subjected  to  artifi- 
cial heat,  they  were  almost  uniformly  restored,  from  a  state  of  insensi- 
bility and  want  of  muscular  power,  to  a  condition  of  comparative  activity. 
Their  temperature  rose,  their  muscular  power  returned,  they  took  food 
when  it  was  presented  to  them,  and  their  secretions  were  renewed ;  and,  if 
this  artificial  assistance  was  sufficiently  prolonged,  and  they  were  supplied 
with  food,  they  recovered.  If  the  heat  was  withdrawn,  however,  before 
the  time  when  the  digested  food  was  ready,  in  sufficient  amount,  to 
supply  the  combustive  process,  they  still  sank  for  want  of  it. 

118.  Various  important  practical  hints  may  be  derived  from  the  con- 
sideration of  these  facts.  There  can  be  no  doubt  that,  in  many  diseases 
of  exhaustion,  the  want  of  power  to  sustain  the  requisite  temperature, 
is  the  immediate  cause  of  death  ;  the  whole  combustible  material  of  the 
body  having  been  exhausted,  and  the  digestive  apparatus  not  being  able 
to  supply  what  is  required.  Now  where  this  is  the  case,  there  is  no 
doubt  that  life  may  be  prolonged,  and  that  recovery  may  be  favoured, 
by  the  judicious  sustentation  of  the  temperature  of  the  body.  This  may 
be  effected  either  by  internal  or  by  external  means.  Of  the  internal,  the 
most  efficient  is  undoubtedly  the  administration  of  Alcoholic  fluids; 
which,  for  reasons  hereafter  to  be  given  {§  495),  will  be  absorbed  into 
the  circulating  system,  when  no  other  alimentary  substance  can  be  taken 
in ;  and  which,  moreover,  exert  a  favourable  influence  by  their  specific 
stimulating  eff'ect  upon  the  nervous  system.  It  is  a  matter  of  familiar 
experience,  that,  in  such  conditions  of  the  body,  the  quantity  of  alcohol 
which  may  be  administered  with  positive  and  evident  benefit,  is  such  as 
would  in  ordinary  circumstances  be  productive  of  the  most  injurious 
results ;  and  this  is  fully  accounted  for  by  the  reflection,  that  it  is  burnt 
off  as  fast  as  it  is  taken  in.  But  a  most  important  adjunct  in  all  such 
cases, — and  in  many  instances  a  substitute  for  alcohol  when  the  latter 
would  be  inadmissible, — will  be  found  in  the  application  of  external  heat; 
and  especially  in  the  subjection  of  the  whole  surface  to  its  influence,  by 
means  of  the  hot-air  bath.  This  is  a  valuable  portion  of  the  treatment, 
in  the  recovering  of  persons  who  have  been  reduced  to  insensibility  by 
suffocation  of  any  kind ;  and  especially  in  cases  of  drowning,  since  the 
heat  of  the  body  is  rapidly  withdrawn  by  the  conducting  power  of  the 
water.  Indeed  it  may  be  stated  as  a  general  rule,  that,  where  the  tem- 
perature of  the  body  is  lowered  from  any  cause,  external  heat  may  be 
advantageously  applied ;  and  much  evidence  has  lately  been  produced  to 
show,  that  the  reparative  processes  by  which  extensive  wounds  are  healed, 
go  on  more  favourably  under  the  contact  of  warm  dry  air,  than  with 
any  other  application. 

119.  On  the  other  hand,  where  the  object  is  to  keep  down  a  tendency 
to  a  too  violent  action,  the  local  application  of  moderate  cold  is  found 
to  be  of  the  greatest  value  ;  all  surgeons  of  eminence  being  now  agreed 
upon  the  efficacy  of  water-dressing  in  restraining  the  inflammatory  pro- 
cess, especially  in  cases  of  wounds  of  the  joints,  in  which  this  action  is 
most  to  be  apprehended.  The  general  application  of  cold  to  the  surface, 
by  means  of  continued  exposure  to  cool  air,  or  by  a  short  immersion  in 


INFLUENCE    OF    HEAT    ON    ANIMALS.  83 

cold  water,  is  frequently  in  the  highest  degree  beneficial,  by  imparting 
tone  to  the  system,  i.  e.,  by  producing  a  firmer  condition  in  the  solids 
which  were  previously  relaxed^  and  more  especially  by  calling  into  action 
the  tonicity  of  the  walls  of  the  blood-vessels,  which  imparts  to  them  an 
increased  resistance,  and  thus  favours  the  regular  and  vigorous  circu- 
lation of  blood,  upon  principles  which  will  be  hereafter  stated  (§  609). 
But  so  far  from  producing  any  permanent  depression  in  the  temperature 
of  the  body,  this  measure  has  a  tendency  to  elevate  it,  by  the  increased 
vigour  it  produces  in  the  circulation ;  hence  the  glow  which  is  experi- 
enced after  the  use  of  the  cold  bath.  If  this  efi'ect  be  not  produced,  and 
a  chilling  of  the  body,  instead  of  an  invigorating  warmth,  be  the  result 
of  the  use  of  cold,  it  is  evident  that  this  cannot  be  beneficial.  The  inju- 
rious results  of  the  too-prolonged  application  of  even  a  moderate  degree 
of  cold,  are  seen  in  the  depression  of  temperature,  without  a  correspond- 
ing reaction,  which  is  the  consequence  of  an  immersion  in  water  of  50^^ 
or  bt)°  prolonged  for  several  hours  ;  and  still  more  in  that  chilling  of  the 
whole  surface,  frequently  productive  of  the  most  serious  consequences, 
which  arises  from  the  evaporation  of  fluid  from  garments  that  have  been 
moistened,  either  by  perspiration  from  within,  or  by  the  fall  of  rain  or 
dew  upon  their  exterior.  There  is  no  doubt  that  the  obstruction  to  the 
continuance  of  the  perspiration,  presented  by  a  covering  already  satu- 
rated with  moisture,  is  one  cause  of  the  injurious  results  that  so  com- 
monly follow  such  an  occurrence ;  but  there  is  as  little  doubt  that  the 
chilling  influence  of  the  external  evaporation  has  a  large  share  in  pro- 
ducing them.  For  experience  shows  that,  if  the  evaporation  be  pre- 
vented by  an  impenetrable  covering,  the  contact  of  a  garment  thoroughly 
saturated  with  moisture  is  not  productive  of  the  same  injurious  conse- 
quences. 

120.  The  practical  importance  of  the  due  comprehension  of  the  prin- 
ciples, upon  which  Heat  and  Cold  should  be  employed,  in  the  treatment 
of  disease  and  the  preservation  of  health,  has  required  this  digression. 
We  now  proceed  to  consider  the  influence  of  temperature  upon  a  certain 
group  of  warm-blooded  animals ;  which  ofiers  a  remarkable  peculiarity 
in  this  respect, — their  power  of  generating  heat  being  for  a  time  greatly 
diminished  or  almost  completely  suspended ;  the  temperature  of  their 
bodies  following  that  of  the  air  around,  so  that  it  may  be  brought  down 
nearly  to  the  freezing-point ;  their  general  vital  actions  being  carried 
on  with  such  feebleness  as  to  be  scarcely  perceptible  ;  and  yet  the  vital 
properties  of  the  tissues  being  retained,  so  that,  when  the  temperature 
of  the  body  is  again  raised,  the  usual  activity  returns.  This  state,  which 
is  called  hybernation,  appears  to  be  as  natural  to  certain  animals,  as 
sleep  is  to  all,  and  it  corresponds  with  sleep  in  its  tendency  to  periodical 
return. 

121.  No  account  can  be  given  of  the  causes  to  which  it  is  due ;  but 
the  condition  of  the  animals  presenting  it  offers  several  points  of  much 
interest.  There  are  some,  as  the  Lagomys,  in  which  it  appears  to  differ 
but  little  from  deep  ordinary  sleep ;  they  retire  into  situations  which 
favour  the  retention  of  their  warmth ;  and  they  occasionally  wake  up, 
and  apply  themselves  to  some  of  the  store  of  food,  which  they  have  pro- 
vided in  the  autumn.     In  other  cases,  a  great  accumulation  of  fat  takes 


84  EXTERNAL   CONDITIONS   OF   VITAL   ACTIVITY. 

place  within  the  body  in  autumn,  favoured  by  the  oily  nature  of  the 
seeds,  nuts,  &c.,  on  which  the  animals  then  feed ;  and  this  serves  the 
purpose  of  maintaining  the  temperature  for  a  sufficient  length  of  time, 
not  indeed  to  the  usual  standard,  but  to  one  not  far  below  it.  The 
state  of  torpor  in  these  animals  is  more  profound  than  that  of  deep  sleep, 
but  it  is  not  such  as  to  prevent  them  from  being  easily  aroused ;  and 
their  respiratory  movements,  though  diminished  in  frequency,  are  still 
performed  without  interruption.  But  in  the  Marmot^  and  in  animals 
which,  like  it,  hybernate  completely,  the  temperature  of  the  body  (owing 
to  the  want  of  internal  power  to  generate  heat)  and  the  general  vital 
activity,  are  proportionably  depressed  ;  the  respiratory  movements  fall 
from  500  to  14  per  hour,  and  are  performed  without  any  considerable 
enlargement  of  chest ;  the  pulse  sinks  from  150  to  15  beats  per  minute  ; 
the  state  of  torpidity  is  so  profound,  that  the  animal  is  with  difficulty 
aroused  from  it ;  and  the  heat  of  the  body  is  almost  entirely  dependent 
upon  the  temperature  of  the  surrounding  air,  not  being  usually  more 
than  a  degree  or  two  above  it.  When  the  thermometer  in  the  air  is 
somewhat  below  the  freezing-point,  that  placed  within  the  body  falls  to 
about  35°;  and  at  this  point  it  may  remain  for  some  time,  without  any 
apparent  injury  to  the  animal,  which  revives  when  subjected  to  a  higher 
temperature.  When,  however,  the  body  is  exposed  to  a  more  intense 
degree  of  cold,  the  animal  functions  undergo  a  temporary  renewal ;  for 
the  cold  seems  to  act  like  any  other  stimulus  in  arousing  them.  The 
respiratory  movements  and  the  circulation  increase  in  activity,  so  as  to 
generate  an  increased  amount  of  heat ;  but  this  amount  is  insufficient  to 
keep  up  the  temperature  of  the  body,  which  is  at  last  depressed  to  a 
degree  inconsistent  with  the  maintenance  of  life ;  and  not  only  the  sus- 
pension of  activity,  but  the  total  loss  of  vital  properties,  is  the  result. 

122.  Now  the  condition  of  a  hybernating  Mammal  closely  resembles 
that  of  a  cold-blooded  animal,  in  regard  to  the  dependence  of  its  bodily 
temperature  upon  external  conditions.  There  is  this  important  diffe- 
rence, however  ; — that  the  reduction  of  the  temperature  of  the  former 
to  60°  or  50°  is  incontpatible  with  a  state  of  activity,  which  is  only  exhi- 
bited when  the  temperature  rises  to  nearly  the  usual  Mammalian  standard ; 
— whilst  a  permanently  low  or  moderate  temperature  is  natural  to  the 
bodies  of  most  cold-blooded  animals,  whose  functions  could  not  be  well 
carried  on  under  a  higher  temperature.  Thus  all  the  muscles  of  a  Frog 
are  thrown  into  a  state  of  permanent  and  rigid  contraction,  by  the 
immersion  of  its  body  in  water  no  warmer  than  the  blood  which  naturally 
bathes  those  of  the  Bird ;  and  we  find,  accordingly,  that  cold-blooded 
animals  which  cannot  sustain  a  high  temperature,  are  provided  with  a 
frigorifying  rather  than  with  a  calorifying  apparatus.  Although  we 
are  accustomed  to  rank  all  animals,  save  Birds  and  Mammals,  under  the 
general  term  cold-hlooded,  yet  there  exist  among  them  considerable  diver- 
sities as  to  the  power  of  generating  heat  within  themselves,  and  of  thus 
rendering  themselves  independent  of  external  variations.  Thus  among 
Reptiles,  it  appears  that  there  are  some  which  can  sustain  a  temperature 
several  degrees  above  that  of  the  atmosphere,  especially  when  the  latter 
is  sinking  ;  and  among  Fishes,  it  is  certain  that  there  are  species, — the 
Thunny  and  Bonito  for  example, — which  are  almost  entitled  to  the 


INFLUENCE  OF  HEAT  ON  ANIMALS.  85 

name  of  warm-blooded  animals,  their  temperature  being  kept  up  to  nearly 
100°,  when  that  of  the  sea  is  about  80°.  It  is  uncertain,  however,  to 
what  extent  it  would  be  depressed,  by  a  lowering  of  that  of  the  sur- 
rounding medium.  The  greatest  power  of  developing  heat  in  cold- 
blooded animals  appears  to  exist,  when  their  bodies  are  reduced  nearly 
to  the  freezing-point ;  and  when  that  of  the  surrounding  air  or  Avater  is 
much  below  it.  Thus  Frogs  have  been  found  alive  in  the  midst  of  ice 
whose  temperature  was  as  low  as  9°,  the  heat  of  their  own  bodies  being 
33°  ;  and  it  has  been  observed  that  even  Animalcules  contained  in  water 
that  is  being  frozen,  are  not  at  once  destroyed,  but  that  each  lives  for 
a  time  in  a  small  uncongealed  space,  where  the  fluid  seems  to  be  kept 
from  solidifying,  by  the  caloric  liberated  from  the  Animalcule. 

123.  The  peculiar  condition  of  the  class  of  Insects,  in  regard  to  its 
heat-producing  power,  exhibits  in  a  very  striking  manner  the  connexion 
between  an  elevated  temperature  and  vital  activity.  In  the  Larva 
state  of  Insects,  the  temperature  of  the  animal  follows  closely  that  of 
the  surrounding  air,  as  in  the  cold-blooded  classes  generally ;  but  it  is 
usually  from  |  to  4"^  above  it.  In  the  Pupa  condition,  which  is  one  of 
absolute  rest  in  most  insects  that  undergo  a  complete  metamorphosis, 
the  temperature  scarcely  rises  above  that  of  the  surrounding  medium ; 
except  at  nearly  the  close  of  the  period,  when  it  is  about  to  burst  its 
envelopes  and  come  forth  as  the  perfect  Insect.  The  temperature 
which  different  Insects  possess  in  their  Imago  state,  varies  in  part  ac- 
cording to  the  species,  and  in  part  with  the  condition  of  the  individual 
in  regard  to  rest  or  activity ;  but  the  same  principle  is  evidently  ope- 
rating in  both  cases,  since  the  variation  existing  amongst  different 
species,  in  regard  to  their  heat-producing  power,  is  closely  connected 
with  the  amount  of  activity  natural  to  them.  The  highest  amount  is 
to  be  found  in  the  industrious  Hive-Bee  and  its  allies,  and  in  the  elegant 
and  sportive  Butterflies,  which  are  almost  constantly  on  the  wing  in 
search  of  food;  next  to  these  come  the  Beetles. of  active  flight ;  and 
lastly  tHose  which  seldom  or  never  raise  themselves  upon  the  wing, 
but  pursue  their  labours  on  the  ground.  The  temperature  of  individual 
Bees  has  been  found  to  be  about  4°  above  that  of  the  atmosphere,  when 
they  are  in  a  state  of  repose ;  but  it  rises  to  10°  or  15°,  when  they  are 
excited  to  activity.  When  they  are  aggregated  together  in  clusters, 
however,  the  temperature  which  they  possess  is  often  as  milch  as  40° 
above  that  of  the  atmosphere.  When  reduced  to  torpidity  by  cold, 
they  still  generate  heat  enough  to  keep  them  from  being  frozen,  unless 
the  cold  be  very  severe ;  and  they  may  be  aroused  by  moderate  excitement 
to  a  state  of  activity,  in  which  the  temperature  rises  to  a  very  conside- 
rable elevation.  Now  although  the  increased  production  of  heat  is  in 
these  cases,  as  in  hybernating  Mammals  similarly  aroused,  the  conse- 
quence  of  the  increased  activity,  there  can  be  no  question  that  it  is  a 
condition  necessary  to  the  continuance  of  that  activity ;  since  we  find 
that,  if  the  temperature  of  the  body  be  again  reduced  by  external  cold, 
the  activity  cannot  be  long  maintained. 

124.  Whilst  the  foregoing  facts  exhibit  the  connexion  between  an 
elevated  temperature,  and  the  most  active  condition  of  the  muscular 
and  nervous  systems,  in  cold-blooded  animals,  there  is  abundant  evi- 


86  EXTERNAL    CONDITIONS   OF   VITAL   ACTIVITY. 

dence  of  the  same  kind  in  regard  to  the  influence  of  Heat  upon  the  pro- 
cesses of  nutrition  and  development.  Thus  the  time  of  emersion  of 
Insect-larvae  from  their  eggs, — or  in  other  words,  the  rate  at  ■which  the 
previous  formative  processes  go  on,  is  entirely  dependent  upon  the  tem- 
perature. In  the  case  of  the  Bird,  we  find  that,  if  the  temperature  be 
not  sufiicient  to  develope  the  egg,  chemical  changes  soon  take  place, 
which  involve  the  loss  of  its  vitality ;  or  if  the  temperature  be  reduced, 
so  low  as  to  prevent  the  occurrence  of  those  changes,  the  loss  of  heat 
is  in  itself  destructive  of  life.  But  this  is  not  the  case  in  regard  to  the 
eggs  of  cold-blooded  animals  in  general ;  for,  like  the  beings  they  are 
destined  to  produce,  they  may  be  reduced  to  a  state  of  complete  inac- 
tion by  a  depression  of  the  external  temperature ;  whilst  a  slight  eleva- 
tion of  this  renews  their  vital  operations,  at  a  rate  corresponding  to  the 
warmth  supplied.  Hence  the  production  of  larvae  from  the  eggs  of 
Insects  may  be  accelerated  or  retarded  at  pleasure ;  and  this  is,  in  fact, 
practised  in  the  rearing  of  Silk-worms,  in  order  to  adapt  the  time  of 
their  emersion  from  the  egg  to  the  supply  of  food  which  is  ready  for 
them.  The  same  may  be  said  in  regard  to  the  eggs  of  other  cold- 
blooded animals ;  those,  for  example,  of  the  minute  Entomostracous 
Crustacea  (Water-Fleas,  &c.),  which  people  our  ditches  and  ponds.  In 
many  of  these,  the  race  is  continued  solely  by  the  eggs,  which  remain 
dormant  through  the  winter  ;  all  the  parents  being  destroyed  by  the  cold. 
The  common  Daphnia  pulex  produces  two  kinds  of  eggs ;  from  one,  the 
young  are  very  speedily  hatched ;  but  the  others,  which  are  produced  in 
the  autumn,  and  enveloped  in  a  peculiar  covering,  do  not  give  birth  to 
the  contained  young  until  the  succeeding  spring.  They  may  be  at  any 
time  hatched,  however,  by  artificial  warmth. 

125.  We  sometimes  find  special  provisions  for  imparting  to  the  eggs 
a  temperature  beyond  that  which  is  natural  to  the  bodies  of  the  parents  ; 
thus  it  has  been  shown  that  in  Serpents,  the  temperature  of  the  poste- 
rior part  of  the  body  rises  considerably,  when  the  eggs  are  lying  in  the 
oviduct,  preparatory  to  being  discharged, — evidencing  a  special  heat- 
producing  power  in  the  surrounding  parts  at  this  period,  which  is  obvi- 
ously for  the  purpose  of  aiding  the  maturity  of  the  eggs.  The  Viper, 
whose  eggs  are  frequently  hatched  in  the  maternal  oviduct,  so  that  the 
young  are  brought  forth  alive,^  is  occasionally  seen  basking  in  the  sun, 
in  such  a  position  as  to  receive  its  strongest  heat  on  the  parts  that  cover 
the  oviduct.  Certain  Birds  have  recourse  to  substitutes  for  the  usual 
method  of  incubation.  The  Tallegalla  of  New  Holland  is  directed  by 
its  remarkable  instinct,  not  to  sit  upon  its  eggs,  but  to  bring  them  to 
maturity  by  depositing  them  in  a  sort  of  hot-bed,  which  it  constructs  of 
decaying  vegetable  matter.  The  Ostrich  is  believed  to  sit  upon  its  eggs, 
when  the  temperature  falls  below  a  certain  standard,  but  to  leave  them 
to  the  influence  of  the  solar  heat  when  this  is  sufficient  to  bring  them 
to  maturity;  and  this  statement  derives  confirmation  from  a  similar 
fact  observed  in  a  Fly-catcher,  which  built  in  a  hot-house  during  several 
successive  years, — the  bird  quitting  its  eggs  when  the  temperature  was 
high,  and  resuming  its  place  when  it  fell.  In  all  these  cases,  as  in 
many  more  which  might  be  enumerated,  we  observe  the  influence  of  an 
elevated  temperature  upon  the  processes  of  development ;  and  the  pro- 


INFLUENCE  OF  HEAT  ON  ANIMALS.  87 

visions  made  by  Nature,  in  the  physical  or  mental  constitution  of  ani- 
mals, for  affording  that  influence.  The  development  of  heat  around  the 
oviduct  of  the  Serpent  is  a  process  over  which  the  individual  has  no 
control,  being  entirely  dependent  upon  certain  organic  changes ;  whilst 
the  imparting  of  warmth  to  its  eggs  by  the  Bird,  either  from  its  own 
body  or  through  artificial  means,  is  committed  to  the  guidance  of  its 
Instinct, — which  same  instinct  leads  it  to  suspend  the  process  whernt~ 
is  not  necessary. 

126.  Phenomena  of  an  equally  interesting  and  instructive  character 
may  be  observed  in  the  history  of  the  Pupa-state  of  Insects ;  which,  in 
those  that  undergo  a  complete  metamorphosis,  may  be  almost  charac- 
terized as  a  re-entrance  into  the  egg.  In  fact  we  shall  obtain  the  most 
correct  idea  of  the  nature  of  that  metamorphosis,  by  considering  the 
Larva  as  an  embryo,  which  comes  forth  from  the  egg  in  a  very  early  and 
undeveloped  condition,  for  the  sake  of  obtaining  materials  for  its  continued 
development,  which  the  egg  does  not  supply  in  sufficient  amount.  When 
these  have  been  digested  and  stored-up  in  the  body,  the  animal  becomes 
completely  inactive,  so  far  as  regards  its  external  manifestations  of  life ; 
and  it  forms  some  kind  of  envelope  for  its  protection,  which  may  not  be 
unaptly  compared  to  the  shell  or  horny  covering  of  the  egg.  Within 
this  are  gradually  developed  the  wings,  legs,  and  other  parts  which  are 
peculiar  to  the  perfect  Insect ;  whilst  even  those  organs,  which  it  pos- 
sesses in  common  with  the  Larva,  are  for  the  most  part  completely 
altered  in  character.  When  this  process  of  development  is  completed, 
the  Insect  emerges  from  its  Pupa-case,  just  as  the  Bird  comes  forth  from 
the  egg;  then  only  does  its  Insect  life  begin,  its  previous  condition 
having  been  that  of  a  Worm ;  and  the  alteration  of  its  character  is  just 
as  evident  in  its  instinctive  propensities,  as  it  is  in  its  locomotive  and 
sensorial  powers. 

127.  Now  this  process  of  development  is  remarkably  influenced  by 
external  temperature ;  being  accelerated  by  genial  warmth,  and  retarded 
by  cold.  There  are  many  Larvae,  which  naturally  pass  into  the  Pupa 
state  during  the  autumn,  remain  in  it  during  the  entire  winter,  and 
emerge  as  perfect  Insects  with  the  return  of  spring.  It  was  found  by 
Reaumur,  that  Pupae,  which  would  not  naturally  have  been  disclosed 
until  May,  might  be  caused  to  undergo  their  metamorphosis  during  the 
depth  of  winter,  by  the  influence  of  artificial  heat ;  whilst,  on  the  other 
hand,  their  change  might  be  delayed  a  whole  year  beyond  its  usual 
time,  by  the  prolonged  influence  of  a  cold  atmosphere.  In  order  to 
hasten  the  development  of  the  pupae  of  the  Social  Bees,  a  very  curious 
provision  is  made.  There  is  a  certain  set,  to  which  the  name  of  Nurse- 
bees  has  been  given,  whose  duty  it  is  to  cluster  over  the  cells  in  which 
the  Nymphs  or  Pupae  are  lying,  and  to  communicate  the  heat  to  them, 
which  is  developed  by  the  energetic  movements  of  their  own  bodies,  and 
especially  by  respiratory  actions  of  extreme  rapidity.  The  nurse-bees 
begin  to  crowd  upon  the  cells  of  the  nymphs,  about  ten  or  twelve  hours 
before  these  last  come  forth  as  perfect  Bees.  The  incubation  (for  so  it 
may  be  called)  is  very  assiduously  persevered  in  during  this  period  by 
the  Nurse-bees ;  when  one  quits  its  cell,  another  takes  its  place ;  and 
the  rapidity  of  the  respiratory  movements  increases,  until  they  rise  to 


k 


88  EXTERNAL    CONDITIONS    OF   VITAL   ACTIVITY. 

130  or  140  per  minute,  so  as  to  generate  the  greatest  amount  of  heat 
just  before  the  young  bees  are  liberated  from  the  combs.  In  one  in- 
stance, the  thermometer  introduced  among  seven  nursing-bees  stood  at 
92 J°;  the  temperature  of  the  external  air  being  70°.  We  observe  in 
this  curious  propensity  a  manifest  provision  for  accelerating  the  deve- 
lopment of  the  perfect  Insect,  which  requires  (as  already  pointed  out)  a 
higher  temperature  than  the  larva,  in  virtue  of  its  greater  activity.  The 
Nurse-bees  do  not  station  themselves  over  the  cells  which  are  occupied 
by  the  larvae ;  nor  do  they  incubate  the  nymph-cells  with  any  degree  of 
constancy  and  regularity,  until  the  process  of  development  is  approach- 
ing its  highest  point. 

128.  The  influence  of  variations  in  the  Heat  of  the  body  upon  its 
vital  activity,  is  further  manifested  by  the  very  remarkable  experiments 
of  Dr.  Edwards ;  who  has  shown  that  Cold-blooded  animals  live  much 
faster  (so  to  speak)  at  high  temperatures,  than  at  low;  so  that  they  die 
much  sooner,  when  deprived  of  other  vital  stimuli.  Thus  when  Frogs 
were  confined  in  a  limited  quantity  of  water,  and  were  not  permitted  to 
come  to  the  surface  to  breathe,  it  was  found  that  the  duration  of  their 
lives  was  inversely  proportional  to  the  degree  of  heat  of  the  fluid.  Thus 
when  it  was  cooled  down  to  the  freezing-point,  the  frogs  immersed  in  it 
lived  during  from  367  to  498  minutes.  At  the  temperature  of  50°,  the 
duration  of  their  lives  was  from  350  to  375  minutes ;  at  72°,  it  was  from 
90  to  35  minutes ;  at  90°,  from  12  to  32  minutes ;  and  at  108°  death 
was  almost  instantaneous.  The  prolongation  of  life  at  the  lower  tempe- 
ratures was  not  due  to  torpidity,  for  the  animals  perform  the  functions  of 
voluntary  motion,  and  enjoy  the  use  of  their  senses ;  but  it  is  occasioned 
by  their  diminished  activity,  which  occasions  a  less  demand  for  air.  On 
the  other  hand,  the  elevation  of  temperature  increases  the  demand  for 
air,  and  causes  speedier  death  when  it  is  withheld ;  by  increasing  the 
general  agility.  The  natural  habits  of  these  animals  are  in  correspon- 
dence with  these  facts.  During  the  winter,  the  influence  of  a  sufi&cient 
amount  of  aerated  water  upon  their  exterior  serves  to  maintain  the  re- 
quired amount  of  respiration  through  the  skin,  so  that  they  are  not 
obliged  to  come  to  the  surface  to  take  in  air  by  the  mouth.  As  the 
season  advances,  however,  their  activity  increases,  a  larger  amount  of 
respiration  is  required,  and  the  animals  are  obliged  to  come  frequently 
to  the  surface  to  breathe.  During  summer,  the  yet  higher  temperature 
calls  forth  an  increased  energy  and  activity  in  all  the  vital  functions ; 
the  respiration  must  be  proportionably  increased ;  the  action  of  the  air 
upon  the  cutaneous  surface,  as  well  as  upon  the  lungs,  is  required ;  and 
if  the  animals  are  prevented  from  quitting  the  water  to  obtain  this,  they 
die,  as  soon  as  the  warmth  of  the  season  becomes  considerable.  The 
result  of  experiments  on  Fishes,  in  regard  to  the  deprivation  or  limited 
supply  of  the  air  contained  in  the  water  in  which  they  are  immersed,  is 
exactly  similar ;  the  duration  of  life  being  inversely  as  the  temperature. 
And  precisely  the  same  has  been  ascertained  w^ith  respect  to  hyberna- 
ting  Mammals ;  which,  as  already  remarked,  are  for  a  time  reduced,  ii 
all  such  conditions,  to  the  level  of  cold-blooded  animals. 

129.  The  energy  of  the  reparative  actions  of  Animals  is  much  influ- 
enced by  temperature,  as  might  be  inferred  from  what  has  been  just 


INFLUENCE  OF  HEAT  ON  ANIMALS.  89 

said  of  their  nutritive  and  developmental  operations.  Thus  the  rate  at 
which  regeneration  of  lost  parts,  like  that  of  the  ordinary  process  of 
budding,  takes  place  in  the  common  Hydra  (Fresh-water  Polype),  is  in 
close  accordance  with  the  temperature  in  which  it  lives ;  and  in  like 
manner,  the  healing  of  wounds  in  Frogs  takes  place  more  rapidly  in 
summer  than  in  winter.  In  many  of  the  higher  animals,  indeed,  -it 
appears  that  the  complete  regeneration  of  parts  requires  a  higher  tem- 
perature than  is  necessary  to  sustain  the  ordinary  vital  activity.  Thus 
it  has  been  found  that  the  common  Triton  (water-newt)  can  reproduce  a 
limb  that  has  been  cut  off,  if  it  be  kept  at  a  temperature  of  from  58°  to 
75°;  but  cannot  do  so  if  a  less  amount  of  heat  be  afforded  to  it.  And 
in  like  manner,  the  snail  can  regenerate  its  head,  if  it  be  kept  in  a  warm 
atmosphere,  but  not  at  a  low  temperature.  Now  it  has  been  justly  re- 
marked by  Mr.  Paget,  that  the  process  of  development  seems  to  require 
a  higher  amount  of  vital  force  than  simple  growth  ;  and  we  see  that  the 
relation  already  pointed  out  between  Heat  and  Vital  force,  here  holds 
good  in  such  a  marked  degree,  as  to  afford  a  strong  confirmation  of  the 
idea  of  their  mutual  relationship. 

130.  It  is  quite  conformable  to  the  same  principle,  that  we  should 
find  Cold-blooded  animals  able  to  sustain  the  deprivation  of  food  during 
a  much  longer  period,  at  cold  temperatures,  than  at  warm.  The  case 
is  precisely  the  reverse,  however,  in  regard  to  most  Warm-blooded  ani- 
mals ;  since  in  them  a  due  supply  of  food  is  a  condition  absolutely  ne- 
cessary (as  we  have  already  seen)  for  the  maintenance  of  that  amount 
of  bodily  heat,  whose  loss  is  fatal  to  them ;  and  exposure  to  a  low  tem- 
perature will  of  course  more  speedily  bring  about  that  crisis.  Hence  it 
is  that  Cold  and  Starvation  combined  are  so  destructive  to  life.  But  in 
this  respect  also,  the  hybernating  Mammals  correspond  with  the  cold- 
blooded classes ;  their  power  of  abstinence  being  inversely  as  the  tem- 
perature of  their  bodies. 

131.  We  have  seen  that  the  animals  termed  cold-blooded  are  greatly 
influenced  as  to  the  temperature  of  their  bodies,  by  the  temperature  of 
the  surrounding  medium  ;  although  many  of  them  are  endowed  with  the 
power  of  keeping  themselves  a  certain  number  of  degrees  above  it.  Now 
the  consequence  of  this  is,  that  all  of  them  which  are  subject  to  any 
considerable  and  prolonged  amount  of  cold,  pass  into  a  state  of  more  or 
less  complete  inactivity  during  its  continuance ;  which  state  bears  a  close 
correspondence  with  the  hybernation  of  certain  Mammalia.  Among  the 
Reptiles  of  cold  and  temperate  countries,  this  torpid  state  uniformly 
occupies  a  considerable  part  of  the  year ;  as  it  does  also  with  Insects, 
terrestrial  Molluscs,  and  other  Invertebrated  animals,  which  are  subject 
to  the  influence  of  the  cold.  On  the  other  hand.  Fishes,  Crustacea,  and 
other  marine  animals,  do  not  usually  appear  to  pass  into  a  state  of  tor- 
pidity ;  the  temperature  of  the  medium  they  inhabit  never  undergoing 
nearly  so  great  a  degree  of  depression,  as  that  of  the  atmosphere.  The 
amount  of  change  necessary  to  produce  this  effect,  or  on  the  other  hand 
to  call  the  animals  from  a  state  of  torpidity  to  one  of  active  energy, 
differs  for  different  species ;  and  there  is  probably  a  considerable  diffe- 
rence even  among  individuals  of  the  same  species,  according  to  the  tem- 
perature under  which  they  habitually  live.     Thus  one  animal  may  remain 


I 


yU  EXTERNAL   CONDITIONS   OF   VITAL   ACTIVITY. 

torpid  under  a  degree  of  warmth  which  will  be  sufficient  to  arouse 
another  of  the  same  kind,  accustomed  to  a  somewhat  colder  climate ; 
because  the  stimulus  is  relatively  greater  to  the  latter. 

132.  It  was  observed  by  Mr.  Darwin,  that  at  Bahia  Blanca  in  South 
America,  the  first  appearance  of  activity  in  animal  and  vegetable  life,  a 
few  days  before  the  vernal  equinox,  presented  itself  under  a  mean  tem- 
perature of  58°,  the  range  of  the  thermometer  in  the  middle  of  the  day 
being  between  60°  and  70°.  The  plains  were  ornamented  by  the  flowers 
of  a  pink  wood-sorrel,  wild  peas,  evening  primroses,  and  geraniums ; 
the  birds  began  to  lay  their  eggs ;  numerous  beetles  were  crawling  about ; 
and  lizards,  the  constant  inhabitants  of  a  sandy  soil,  were  darting  about 
in  every  direction.  Yet  a  few  days  peviously,  it  seemed  as  if  nature 
had  scarcely  granted  a  living  creature  to  this  dry  and  arid  country ; 
and  it  was  only  by  digging  in  the  ground  that  their  existence  had  been 
discovered, — several  insects,  large  spiders,  and  lizards,  having  been  found 
in  a  half-torpid  state.  Now  at  Monte  Video,  four  degrees  nearer  the 
Equator,  the  mean  temperature  had  been  above  58°  for  some  time  pre- 
viously, and  the  thermometer  rose  occasionally  during  the  middle  of  the 
day  to  69°  or  70°;  yet  with  this  elevated  temperature,  almost  equivalent 
to  the  full  summer  heat  of  our  own  country,  almost  every  beetle,  several 
genera  of  spiders,  snails,  and  land-shells,  toads  and  lizards,  were  still 
lying  torpid  beneath  stones.  We  have  seen  that  at  Bahia  Blanca,  whose 
climate  is  but  a  little  colder,  this  same  temperature,  with  a  rather  less 
extreme  heat,  was  sufficient  to  awake  all  orders  of  animated  beings ; — 
showing  how  nicely  the  required  degree  of  stimulus  is  adapted  to  the 
general  climate  of  the  place,  and  how  little  it  depends  on  absolute  tem- 
perature. 

133.  We  may  learn  much  from  the  Geographical  distribution  of  the 
diiferent  species  of  cold-blooded  animals,  in  regard  to  the  influence  of 
temperature  on  Animal  life.  No  general  inferences  of  this  kind  can 
be  found  upon  the  distribution  of  warm-blooded  animals ;  since  their 
own  heat-evolving  powers  make  them  in  great  degree  independent  of 
external  warmth.  And  it  is  probably  from  the  distribution  of  the 
marine  tribes,  whose  extension  is  less  influenced  by  local  peculiarities, 
that  the  most  satisfactory  deductions  are  to  be  drawn.  In  regard  to 
the  class  of  Crustacea,  which  is  the  one  that  has  been  most  fully  inves- 
tigated in  this  respect,  the  following  principles  have  been  pointed  out 
by  M.  Milne  Edwards ;  and  they  are  probably  more  or  less  applicable 
to  most  others. 

I.  The  varieties  of  form  and  organization  manifest  themselves  more, 
in  proportion  as  we  pass  from  the  Polar  Seas  towards  the  Equator. 

II.  The  diff'erences  of  form  and  organization  are  not  only  more  nume- 
rous and  more  characteristic  in  the  warm  than  in  the  cold  regions  ofi 
the  globe ;  they  are  also  more  important. 

III.  Not  only  are  those  Crustacea,  which  are  most  elevated  in  thei 
scale,  deficient  in  the  Polar  regions ;  but  their  relative  number  increases 
rapidly  as  we  pass  from  the  Pole  towards  the  Equator. 

IV.  When  we  compare  together  the  Crustacea  of  diff*erent  parts  of 
the  world,  we  observe  that  the  average  size  of  these  animals  is  con- 


INFLUENCE  OF  HEAT  ON  ANIMALS.  91 

siderably  greater  in  tropical  regions,  than  in  the  temperate  or  frigid 
climes. 

V.  It  is  where  the  species  are  most  numerous  and  varied,  and  where 
they  attain  the  greatest  size, — in  other  words,  where  the  temperature 
is  most  elevated, — that  the  peculiarities  of  structure  which  characterize 
the  several  groups,  are  most  strongly  manifested.  —  — 

VI.  Lastly,  there  is  a  remarkable  coincidence  between  the  tempera- 
ture of  diflferent  regions,  and  the  prevalence  of  certain  forms  of  Crus- 
tacea. 

134.  Now  although,  as  appears  from  the  foregoing  general  state- 
ments, the  number  of  species  of  Crustacea  inhabiting  the  colder  seas 
bears  a  very  small  proportion  to  that  which  is  found  within  the  tropics, 
and  although  the  species  formed  to  inhabit  cold  climates  are  so  far  in- 
ferior both  as  to  size,  and  as  to  perfection  of  development,  yet  it  doefe 
not  follow  that  the  same  proportion  exists  in  regard  to  the  relative 
amount  of  Crustacean  life  in  the  two  regions ;  for  this  depends  upon 
the  multiplication  of  individuals.  In  fact  it  may  be  questioned  whether 
there  is  any  inferiority  in  this  respect ;  so  abundant  are  some  of  the 
smaller  species  in  the  Arctic  and  Antarctic,  as  well  as  in  the  Temperate 
seas.  Thus  we  see  that  a  low  range  of  temperature  is  as  well  adapted 
to  sustain  their  life,  as  a  higher  range  is  to  call  forth  those  larger  and 
more  fully-developed  forms,  which  abound  in  the  tropical  ocean.  There 
is  an  obvious  reason  why  the  seas  of  the  frigid  zones  should  be  much 
more  abundantly  peopled  than  the  layid ;  the  mean  temperature  of  the 
former  being  much  higher.  And  it  would  almost  seem  as  if  Nature 
had  intended  to  compensate  for  the  dreariness  and  desolation  of  the  one, 
by  the  profuseness  of  life  which  she  "has  fitted  the  other  to  support. 

135.  The  influence  of  Temperature  in  producing  a  variation  in  the 
size  of  individual  Animals  of  any  one  species,  is  not  so  strongly  marked 
as  it  is  in  the  case  of  Plants  ;  for  this  reason,  perhaps,  that  an  amount  of 
continued  depression  or  elevation,  which  might  be  sustained  by  a  Plant, 
but  which  would  exert  a  modifying  influence  upon  its  growth,  would  be 
fatal  to  an  Animal  formed  to  exist  in  the  same  climate.  Instances  are 
not  wanting,  however,  in  which  such  a  modifying  influence  is  evident ; 
and  these,  as  might  be  anticipated,  are  to  be  met  with  chiefly  among 
the  cold-blooded  tribes.  Thus  the  Bulimus  rosaceus,  a  terrestrial  mol- 
lusc, is  found  on  the  mountains  of  Chili  of  so  much  less  a  size  than  that 
which  it  attains  on  the  coast,  as  to  have  been  described  as  a  distinct 
species.  And  the  Littorina  petrcea  found  on  the  south  side  of  Plymouth 
Breakwater,  acquires,  from  its  superior  exposure  to  light  and  heat 
(though  perhaps  also  from  the  greater  supply  of  nutriment  which  it 
obtains),  twice  the  size  common  to  individuals  living  on  the  north  side 
within  the  harbour. — The  following  circumstance  shows  the  favourable 
influence  of  an  elevated  temperature,  in  producing  an  unusual  prolific- 
ness  in  Fish;  which  must  be  connected  with  general  vital  activity. 
Three  pairs  of  Gold-fish  were  placed,  some  years  since,  in  one  of  the 
engine-dams  or  ponds  common  in  the  manufacturing  districts,  into 
which  the  water  from  the  engine  is  conveyed  for  the  purpose  of  being 
cooled ;  the  average  temperature  of  such  dams  is  about  80°.  At  the 
end  of  three  years,  the  progeny  of  these  Fish,  which  Were  accidentally 


92  EXTERNAL   CONDITIONS   OF  VITAL   ACTIVITY. 

poisoned  by  verdigris  mixed  with  the  refuse  tallow  from  the  engine, 
were  taken  out  by  wheelbarrowfuls.  It  is  not  improbable  that  the 
unusual  supply  of  aliment,  furnished  by  the  refuse  grease  that  floats 
upon  these  ponds  (which  would  impede  the  cooling  of  the  water,  if  it 
were  not  consumed  by  the  Fish),  contributed  with  the  high  temperature 
to  this  unusual  fecundity. 

136.  Although  h  very  low  temperature  is  positively  inconsistent  with 
the  continuance  of  vital  activity^  in  Animals  as  in  Plants,  yet  we  find 
that  even  very  severe  cold  is  not  necessarily  destructive  of  the  vital 
propei'ties  of  organized  tissues ;  so  that,  on  a  restoration  of  the  proper 
amount  of  heat,  their  functions  may  continue  as  before.  Of  this  we 
have  already  noticed  an  example,  in  the  case  of  frost-bitten  limbs  ;  but 
the  fact  is  much  more  remarkable,  when  considered  in  reference  to  the 
whole  body  of  an  animal,  and  the  complete  suspension  of  all  its  func- 
tions. Yet  it  is  unquestionably  true,  not  only  of  the  lowest  and  sim- 
plest members  of  the  Animal  kingdom,  but  also  of  Fishes  and  Reptiles. 
In  one  of  Captain  Ross's  Arctic  Voyages,  several  Caterpillars  of  the 
Laria  Rossii  having  been  exposed  to  a  temperature  of  40°  heloiv  zero, 
froze  so  completely,  that,  when  thrown  into  a  tumbler,  they  chinked 
like  lumps  of  ice.  When  thawed,  they  resumed  their  movements,  took 
food,  and  underwent  their  transformation  into  the  Chrysalis  state.  One 
of  them,  which  had  been  frozen  and  thawed  four  times,  subsequently 
became  a  Moth.  The  eggs  of  the  Slug  have  been  exposed  to  a  similar 
degree  of  cold,  Avithout  the  loss  of  their  fertility.  It  is  not  uncommon 
to  meet  in  the  ice  of  rivers,  lakes,  and  seas,  with  Fishes  which  have 
been  completely  frozen,  so  as  to  become  quite  brittle ;  and  which  yet 
revive  when  thawed.  The  same  thing  has  been  observed  in  regard  to 
Frogs,  Newts,  &c. ;  and  the  experiment  of  freezing  and  subsequently 
thawing  them,  has  been  frequently  put  in  practice.  Spallanzani  kept 
Frogs  and  Snakes  in  an  ice-house  for  three  years ;  at  the  end  of  which 
period  they  revived  on  being  subjected  to  warmth. 

137.  It  does  not  appear,  however,  that  the  same  capability  exists,  in 
the  case  of  any  warm-blooded  animals ;  since  if  a  total  suspension*  of 
vital  activity  take  place  in  the  body  of  a  Bird  or  Mammal  for  any  length 
of  time,  in  consequence  of  the  prolonged  application  of  severe  cold,  re- 
covery is  found  to  be  impossible.  The  power  which  exists  in  these  ani- 
mals, however,  of  generating  a  large  amount  of  heat  within  their  bodies, 
acts  as  a  compensation  for  the  want  of  the  faculty  possessed  by  the 
cold-blooded  tribes ;  since  they  can  resist,  for  a  great  length  of  time  (if  I 
in  their  healthy  or  normal  condition),  the  depressing  influence  of  a  tem- 
perature, sufficiently  low  to  produce  a  complete  suspension  in  the  acti- 
vity of  the  latter. 

138.  It  only  remains  to  say  a  few  words  regarding  the  degree  of  heat 
which  certain  Animals  can  sustain  without  prejudice,  and  which  even  i 
appears  to  be  genial  to  them.  Among  the  higher  classes,  this  range  i 
seems  to  be  capable  of  great  extension.  Thus  many  instances  are  on 
record,  of  a  heat  of  from  250°  to  280°  being  endured,  in  dry  air,  for  ai 
considerable  length  of  time,  without  much  inconvenience;  and  persons 

*  In  the  case  of  hybernating  Mammals,  the  suspension  is  not  total ;  and  if  it  be  ren-  j 
dered  such,  the  same  result  follows  as  in  other  instances. 


INFLUENCE   OF   HEAT   ON   ANIMALS.  93 

who  have  become  habituated  to  this  kind  of  exposure,  can  (with  proper 
precautions)  sustain  a  temperature  of  from  350°  to  500°.  In  all  such 
cases,  however,  the  real  heat  of  the  body  undergoes  very  little  eleva- 
tion ;  for,  by  means  of  the  copious  evaporation  from  its  surface,  the  ex- 
ternal heat  is  prevented  from  acting  upon  it.  But  if  this  evaporation 
be  prevented,  either  by  an  insufficiency  in  the  supply  of  fluid  from- 
within,  or  by  the  saturation  of  the  surrounding  air  with  moisture,  the 
temperature  of  the  body  begins  to  rise ;  and  it  is  then  found,  that  it 
cannot  undergo  an  elevation  of  more  than  a  few  degrees,  without  fatal 
consequences.  Thus  in  several  experiments  which  have  been  tried  on 
different  species  of  warm-blooded  animals,  for  the  purpose  of  ascertain- 
ing the  highest  temperature  to  which  the  body  could  be  raised  without 
the  destruction  of  life,  it  was  found  that  as  soon  as  the  heat  of  the  body 
had  been  increased,  by  continued  immersion  in  a  limited  quantity  of  hot 
air  (which  would  soon  become  charged  with  moisture),  to  from  9° — 13° 
above  the  natural  standard,  the  animals  died.  In  general  Mammals 
die,  w^hen  the  temperature  of  their  bodies  is  raised  to  about  111°;  the 
heat  which  is  natural  to  the  bodies  of  Birds.  The  latter  are  killed  by 
an  equal  amount  of  elevation  of  bodily  heat  above  their  natural  standard. 

139.  Hence  we  see  that  the  actual  range  of  temperature,  within 
which  vital  activity  can  be  maintained  in  warm-blooded  aniniuls,  is  ex- 
tremely limited ;  a  temporary  elevation  of  the  bodily  heat  to  13°  above 
the  natural  standard,  or  a  depression  to  30°  below  it,  being  positively 
inconsistent,  not  merely  with  the  continuance  of  vital  operations,  but 
also  with  the  preservation  of  vital  properties  :  and  a  continued  departure 
from  that  standard,  to  the  extent  of  only  a  very  few  degrees  above  or 
below  it,  being  very  injurious.  The  provisions  with  which  these  animals 
are  endowed,  for  generating  heat  in  their  interior,  so  as  to  supply  the 
external  deficiency,  and  for  generating  cold  (so  to  speak),  when  the  ex- 
ternal temperature  is  too  high,  are  therefore  in  no  respect  superfluous  : 
but  are  positively  necessary  for  the  maintenance  of  the  life  of  such  ani- 
mals, in  any  climate,  save  one  whose  mea7i  should  be  conformable  to 
their  standard,  and  w^hose  extremes  should  never  vary  more  than  a  very 
few  degrees  above  or  below  it.  Such  a  climate  does  not  exist  on  the 
surface  of  the  earth. 

140.  The  range  of  external  temperature,  within  which  cold-blooded 
animals  can  sustain  their  activity,  is  much  more  limited,  as  well  in  regard 
to  its  highest  as  to  its  lowest  point ;  notwithstanding  that  the  range  of 
bodily  heat,  which  is  consistent  with  the  maintenance  of  their  life,  is  so 
much  greater.  In  those  which,  like  the  Frog,  have  a  soft  moist  skin, 
which  permits  a  copious  evaporation  from  the  surface,  a  considerable 
amount  of  heat  may  be  resisted,  provided  the  air  be  dry,  and  the  supply 
of  fluid  from  within  be  maintained.*  But  immersion  in  water  of  the 
temperature  of  108°,  is  almost  immediately  fatal.  In  many  other  cold- 
blooded animals,  elevation  of  the  temperature  induces  a  state  of  tor- 

*  The  Frog  has  a  remarkable  provision  for  this  purpose ;  in  a  bladder,  which  is 
structurally  analogous  to  our  Urinary  bladder,  but  which  has  for  its  chief  function  to 
contain  a  store  of  fluids  for  the  exhaling  process.  It  has  been  noticed  that,  when  this 
store  is  exhausted  by  continued  exposure  of  the  animal  to  a  warm  dry  atmosphere,  the 
bladder  becomes  full  again,  when  the  animal  is  placed  in  a  moist  situation,  even  though 
it  take  in  no  liquid  by  its  mouth. 


i 


94  EXTERNAL    CONDITIONS    OF    VITAL   ACTIVITY. 

pidity,  analogous  to  that  which  is  produced  by  its  depression.  Thus 
the  Helix  pomatia  (Edible  Snail)  has  been  found  to  become  torpid  and 
motionless  in  water  at  112°;  but  to  recover  its  energy  when  placed  in 
a  colder  situation.  It  would  seem  to  be  partly  from  this  cause,  but 
partly  also  from  the  deprivation  of  moisture,  that  the  liottest  part  of  the 
tropical  year  brings  about  a  cessation  of  activity  in  many  tribes  of  cold- 
blooded animals,  as  complete  as  that  which  takes  place  during  the  winter 
of  temperate  climates. 

141.  The  highest  limit  of  temperature  compatible  with  the  life  of 
Fishes  has  not  been  certainly  ascertained :  and  it  appears  probable  that 
there  are  considerable  variations  in  this  respect  amongst  different  species. 
Thus  it  is  certain  that  there  are  some  which  are  killed  by  immersion  in 
water  at  104°;  whilst  it  is  also  certain  that  others  cannot  only  exist,  but 
can  find  a  congenial  habitation,  in  water  of  113°,  or  even  of  120°;  and 
examples  of  the  existence  of  Fishes  in  thermal  springs  of  a  much  higher 
temperature  than  this,  have  been  put  on  record.  Various  fresh  water 
Mollusca  have  been  found  in  thermal  springs,  the  heat  of  which  is  from 
100°  to  145°.  Rotifera  and  other  animalcules  have  been  met  with  in 
water  at  112°.  Larvae  of  Tipulse  have  been  found  in  hot  springs  of 
205°  ;  and  small  black  beetles,  which  died  when  placed  in  cold  water,  in 
the  hot  sulphur  baths  of  Albano.  Entozoa  inhabiting  the  bodies  of 
Mammalia  and  of  Birds  must  of  course  be  adapted  to  a  constant  tem- 
perature of  from  98°  to  110° ;  and  they  become  torpid  when  exposed  to 
a  cool  atmosphere.  These  lowly  organized  animals  seem  more  capable 
of  resisting  the  effects  of  extreme-  heat,  than  any  others ; — at  least  if 
we  are  to  credit  the  statement,  that  the  Entozoa  inhabiting  the  intestines 
of  the  Carp  have  been  found  alive,  when  the  Fish  was  brought  to  table 
after  being  boiled.  In  all  such  cases,  it  is  to  be  remembered,  that  the 
heat  of  the  animal  body  must  correspond  with  that  of  the  fluid  in  which 
it  is  immersed ;  and  we  have  here,  therefore,  evident  proof  of  the  com- 
patibility of  vital  activity,  in  certain  cases,  with  a  very  elevated  tempe- 
rature. Additional  and  more  exact  observations,  however,  are  much 
wanting  on  this  subject. 

3.    Of  Electricity,  as  a  Condition  of  Vital  Activity. 

142.  Much  less  is  certainly  known  with  respect  to  the  ordinary  influ- 
ence of  this  agent,  than  in  regard  to  either  of  the  two  preceding ;  and 
yet  there  can  be  little  doubt,  from  the  effects  we  observe  when  it  is  pow- 
erfully applied,  as  well  as  from  our  knowledge  of  its  connexion  with  all 
Chemical  phenomena,  that  it  is  in  constant  though  imperceptible  opera- 
tion. Electricity  differs  from  both  Light  and  Heat  in  this  respect ; — 
that  no  manifestation  of  it  takes  place  so  long  as  it  is  uniformly  diffused, 
or  is  in  a  state  of  equilibrium  ;  but  in  proportion  as  this  equilibrium  is 
disturbed,  by  a  change  in  the  electric  condition  of  one  body,  which  is 
prevented,  by  its  partial  or  complete  insulation,  from  communicating 
itself  to  others,  in  that  proportion  is  a  force  produced,  which  exerts 
itself  in  various  ways  according  to  its  degree.  The  mechanical  effects 
of  a  powerful  charge,  when  passed  through  a  substance  that  is  a  bad 
conductor  of  Electricity,  are  well  known ;  on  the  other  hand,  the  chemical 


OF   ELECTRICITY   AS   A   CONDITION   OF    VITAL  ACTIVITY.  95 

effects  of  even  the  feeblest  current  are  equally  obvious.  The  agency  of 
Electricity  in  producing  Chemical  change  is  the  more  powerful,  in  pro- 
portion as  there  is  already  a  predisposition  to  that  change ;  thus,  the 
largest  collection  of  oxygen  and  hydrogen  gases,  or  of  hydrogen  and 
chlorine,  mingled  together,  may  be  caused  to  unite  by  the  minutest  elec- 
tric spark,  which  brings  into  the  condition  required  for  their  active 
exercise,  the  mutual  aflSnities  that  were  previously  dormant.  Hence  it 
cannot  but  be  inferred,  that  its  agency  in  the  Chemical  phenomena  of 
living  bodies  must  be  of  an  important  character  :  but  this  may  probably 
be  exerted  rather  in  the  way  of  aiding  decomposition,  than  of  producing 
new  combinations,  to  which  (as  we  have  seen)  Light  appears  to  be  the 
most  effectual  stimulus.  Thus  it  has  been  shown  that  pieces  of  meat, 
that  have  been  electrified  for  some  hours,  pass  much  more  rapidly  into 
decomposition,  than  similar  pieces  placed  under  the  same  circumstances, 
but  not  electrified.  And  in  like  manner,  the  bodies  of  animals  that  have 
been  killed  by  electric  shocks,  have  been  observed  to  putrefy  much  more 
readily  than  those  of  similar  animals  killed  by  an  injury  to  the  brain. 
It  is  well  known,  moreover,  that  in  thundery  w^eather,  in  which  the 
electric  state  of  the  atmosphere  is  much  disturbed,  various  fluids  con- 
taining organic  compounds,  such  as  milk,  broth,  &c.,  are  peculiarly  dis- 
posed to  turn  sour ;  and  that  saccharine  fluids,  such  as  the  wort  of  brewers, 
are  extremely  apt  to  pass  into  the  acetous  fermentation. 

143.  The  actual  amount  of  influence,  however,  which  Electricity  exerts 
over  a  growing  Plant  pr  Animal,  can  scarcely  be  estimated.  It  would, 
perhaps,  be  the  most  correct  to  say,  that  the  state  of  Electric  equilibrium 
is  that  which  is  generally  most  favourable  ;  and  we  find  that  there  is  a 
provision  in  the  structure  of  most  living  beings,  for  maintaining  such  an 
equilibrium, — not  only  between  the  different  parts  of  their  own  bodies, 
but  also  between  their  own  fabrics  and  the  surrounding  medium.  Thus 
a  charge  given  to  any  part  of  a  Plant  or  Animal,  is  immediately  diffused 
through  its  whole  mass  ;  and  though  Organized  bodies  are  not  sufficiently 
good  conductors  to  transmit  very  powerful  shocks  without  being  them- 
selves affected,  yet  a  discharge  of  any  moderate  quantity  may  be  effected 
through  them,  without  any  permanent  injury, — and  this  more  especially 
if  it  be  made  to  take  place  slowly.  Noav  the  points  on  the  surfaces  of 
Plants  appear  particularly  adapted  to  effect  this  transmission ;  thus  it 
has  been  found  that  a  Ley  den  jar  might  be  discharged  by  holding  a  blade 
of  grass  near  it,  in  one  third  of  the  time  required  to  produce  the  same 
effect  by  means  of  a  metallic  point ;  and  an  Electroscope  furnished  with 
Vegetable  points  has  been  found  to  give  more  delicate  indications  of  the 
electric  state  of  the  atmosphere,  than  any  other.  Plants  designed  for 
a  rapid  growth  have  generally  a  strong  pubescence  or  downy  covering ; 
and  it  does  not  seem  improbable  that  one  purpose  of  this  may  be,  to 
maintain  that  equilibrium  between  themselves  and  the  atmosphere,  which 
would  otherwise  be  disturbed  by  the  various  operations  of  vegetation, 
and  especially  by  the  process  of  evaporation,  which  takes  place  with 
such  activity  from  the  surface  of  the  leaves. 

144.  There  appears  to  be  sufficient  evidence  that,  during  a  highly 
electrical  state  of  the  atmosphere,  the  growth  of  the  young  shoots  of 
certain  plants  is  increased  in  rapidity ;  but  it  would  be  wrong  thence  to 


L 


96  EXTERNAL   CONDITIONS    OF   VITAL   ACTIVITY. 

infer  that  this  excitement  is  useful  to  the  process  of  Vegetation  in  gene- 
ral, or  that  the  same  kind  of  electric  excitement  universally  operates  to 
the  benefit  or  injury  of  the  Plant.  From  some  experiments  recently 
made  it  would  appear,  that  potatoes,  mustard,  and  cress,  cinerarias, 
fuchsias,  and  other  plants,  have  their  development,  and,  in  some  in- 
stances, their  productiveness,  increased  by  being  made  to  grow  between 
a  copper  and  a  zinc  plate,  connected  by  a  conducting  wire  ;  while,  on 
the  other  hand,  geraniums  and  balsams  are  destroyed  by  the  same  in- 
fluence. The  transmission  of  a  series  of  moderate  sparks  through  plants, 
in  like  manner,  has  been  found  to  accelerate  the  growth  of  some,  and  to 
be  evidently  injurious  to  others.  It  is  not  unreasonable  to  suppose, 
that,  as  a  great  variety  of  chemical  processes  are  constantly  taking  place 
in  the  growing  plant,  an  electric  disturbance,  which  acts  as  a  stimulus 
to  some,  may  positively  retard  others ;  and  that  its  good  or  evil  results 
may  thus  depend  upon  the  balance  between  these  individual  effects. 
This  would  seem  the  more  likely  from  the  circumstance,  that,  in  the 
process  of  Germination,  the  chemical  changes  concerned  in  which  are  of 
a  simpler  character.  Electricity  seems  to  have  a  more  decided  and  uni- 
form influence.  The  conversion  of  the  starch  of  the  seed  into  sugar, 
which  is  an  essential  part  of  this  change,  involves  the  liberation  of  a 
large  quantity  of  carbonic,  and  of  some  acetic  acid.  Now  as  all  acids 
are  negative,  and  as  like  electricities  repel  each  other,  it  maybe  inferred 
that  the  seed  is  at  that  time  in  an  electro-negative  condition ;  and  it  is 
accordingly  found  that  the  process  of  germination  may  be  quickened,  by 
connexion  of  the  seed  with  the  negative  pole  of  a  feeble  galvanic  appa- 
ratus, whilst  it  is  retarded  by  a  similar  connexion  with  the  positive  pole. 
A  similar  acceleration  may  be  produced  by  the  contact  of  feeble  alkaline 
solutions,  which  favour  the  liberation  of  the  acids ;  whilst,  on  the  same 
principle,  a  very  small  admixture  of  acid  in  the  fluid  with  which  the 
seed  is  moistened,  is  found  to  produce  a  decided  retardation. 

145.  It  is  well  known  that  Trees  and  Plants  may  be  easily  killed  by 
powerful  electric  shocks  ;  and  that,  when  the  charge  is  strong  enough 
(as  is  the  case  of  a  stroke  of  lightning),  violent  mechanical  efi"ects, — as 
the  rending  of  trunks,  or  even  the  splitting  and  scattering  of  minute 
fragments, — are  produced  by  it.  But  it  has  also  been  ascertained,  that 
charges  which  produce  no  perceptible  influence  of  this  kind,  may  destroy 
the  life  of  Plants  ;  though  the  efiect  is  not  always  immediate.  In  par- 
ticular it  has  been  noticed,  that  slips  and  grafts  are  prevented  from 
taking  root  and  budding.  There  can  be  little  doubt  that,  in  these  in- 
stances, a  change  is  efi'ected  in  the  chemical  state  of  the  solids  or  fluids ; 
although  no  structural  alteration  is  perceptible. 

146.  In  regard  to  the  influence  of  Electricity  upon  the  Organic  func- 
tions of  Animals,  still  less  is  certainly  known ;  but  there  is  evidence  that 
it  may  act  as  a  powerful  stimulant  in  certain  disordered  states  of  them. 
Thus  in  Amenorrhoea,  a  series  of  slight  but  rapidly-repeated  electric 
shocks  will  often  bring  on  the  catamenial  flow ;  and  it  is  certain  that 
chronic  tumours  have  been,  dispersed,  and  dropsies  relieved  by  the  ex- 
citement of  the  absorbent  process,  through  similar  agency.  In  fact, 
there  is  strong  reason  to  believe,  that  Electricity  may  be  advantageously 


OF   MOISTURE  AS   A   CONDITION   OF   VITAL  ACTIVITY.  97 

employed  remedially  in  many  states  of  disordered  nutrition ;  in  virtue 
of  its  power  of  modifying  the  operations  of  the  Vital  forces. 

147.  The  closest  relations  of  Electricity,  however,  are  with  the  proper 
Animal  functions;  for  these,  as  will  be  shown  hereafter,  are  more 
directly  and  obviously  subject  to  its  influence,  than  are  the  Organic. 
Thus  Electricity,  when  transmitted  along  a  Nerve,  whether  sensory  olil 
motor,  a  nerve -of  "special"  or  one  of  "common"  sensation,  is  capable 
of  calling  forth  all  the  actions  of  which  that  nerve  is  the  instrument ; 
and,  when  brought  to  bear  on  a  Muscle,  it  immediately  excites  a  con- 
tractile movement.  It  is  probably  through  the  influence  of  this  agent 
upon  the  Nervous  system,  that  electric  states  of  the  atmosphere  induce 
in  certain  individuals  a  degree  of  languor  and  depression,  which  cannot 
be  accounted  for  in  any  other  way.  An  instance  is  on  record,  in  which 
the  atmosphere  was  in  such  an  extraordinary  state  of  electric  disturbance, 
that  all  pointed  bodies  within  its  influence  exhibited  a  distinct  luminosity  ; 
and  it  was, noticed,  that  all  the  persons  who  were  exposed  to  the  agency 
of  this  highly  electrified  air,  experienced  spasms  in  the  limbs  and  an  ex- 
treme state  of  lassitude. 

148.  Animals,  like  Plants,  are  liable  to  be  killed  by  shocks  of  Elec- 
tricity ;  even  when  these  are  not  sufiiciently  powerful  to  occasion  any 
obvious  physical  change  ii:!  their  structure.  But,  as  formerly  mentioned 
(§  69),  there  can  be  no  doubt  that  minute  changes  may  be  produced  in 
their  delicate  parts,  which  are  quite  sufficient  to  account  for  the  destruc- 
tion of  their  vitality,  even  though  these  can  only  be  discerned  with  the 
microscope.  The  production  of  changes  in  the  Chemical  arrangement 
of  their  elements,  is,  however,  a  much  more  palpable  cause  of  death  ; 
since  it  may  be  fully  anticipated  beforehand,  and  can  easily  be  rendered 
evident.  To  take  one  instance  only ; — it  is  well  known,  that  albumen 
is  made  to  coagulate,  i.  e.,  is  changed  from  its  soluble  to  its  insoluble 
form,  under  the  influence  of  an  electric  current ;  and  it  cannot  be  doubted 
that  the  production  of  this  change  in  the  fluids  of  the  living  body  (almost 
every  one  of  which  contains  albumen),  even  to  a  very  limited  extent,  is 
quite  a  sufficient  cause  of  death,  even  in  animals  that  are  otherwise 
most  tenacious  of  life.  "  I  once  discharged  a  battery  of  considerable 
size,"  says  Dr.  Hodgkin,  "  through  a  common  Earth-worm,  which  would 
in  all  probability  have  shown  signs  of  life  long  after  minute  division. 
Its  death  was  as  sudden  as  the  shock  ;  and  the  semi-transparent  sub- 
stance of  the  animal  was  changed  like  Albumen  which  has  been  exposed, 
to  heat."  1 

4.    Of  Moisture  J  as  a  Condition  of  Vital  Activity. 

149.  Independently  of  the  utility  of  Water  as  an  article  oi  food^  and 
of  the  part  it  performs  in  the  Chemical  operations  of  the  living  body, 
by  supplying  two  of  their  most  important  materials  (oxygen  and  hydro- 
gen), there  can  be  no  doubt  that  a  certain  supply  of  moisture  is  requi- 
site, as  one  of  the  conditions  without  w^iich  no  vital  action  can  go  on. 
It  has  been  already  remarked,  indeed,  that  one  of  the  distinguishing 
peculiarities  of  Organized  structures,  is  the  presence  in  all  of  them  of 
solid  and  liquid  component  parts ;  and  this  in  the  minutest  portions  of 

7 


98  EXTERNAL   CONDITIONS   OF  VITAL  ACTIVITY. 

the  organism,  as  well  as  in  the  aggregate  mass.  And  in  all  the  vital^ 
as  well  as  in  the  chemical  actions,  to  which  these  structures  are  subser- 
vient, the  presence  of  liquid  is  essential.  All  nutrient  materials  must 
be  reduced  to  the  liquid  form,  before  they  can  be  assimilated  by  the 
solids ;  and,  again,  the  solid  matters  which  are  destined  to  be  carried 
ofif  by  excretion,  must  be  again  reduced  to  the  liquid  state,  before  they 
can  be  thus  withdrawn  from  the  body.  The  tissues  in  which  the  most 
active  changes  of  a  purely  vital  character  are  performed, — namely,  the 
Nervous  and  Muscular, — naturally  contain  a  very  large  proportion  of 
water ;  the  former  as  much  as  80  and  the  latter  77  per  cent.  On  the 
other  hand,  in  tissues  whose  function  is  of  a  purely  mechanical  nature, 
such  as  Bone,  the  amount  of  liquid  is  as  small  as  is  consistent  with  the 
maintenance  of  a  certain  amount  of  nutrient  action  in  its  interior.  By 
the  long-continued  application  of  dry  heat  to  a  dead  body,  its  weight 
was  found  to  be  reduced  from  120  pounds  to  no  more  than  12 ;  so  that, 
taking  the  average  of  the  whole,  the  amount  of  water,  not  chemically 
combined,  but  simply  interstitial,  might  be  reckoned  at  as  much  as  90 
per  cent.  It  is  certain,  however,  that  much  decomposition  and  loss  of 
solid  matter  must  have  taken  place  in  this  procedure  ;  and  we  shall  pro- 
bably estimate  the  proportion,  more  accurately,  if  we  regard  the  weight 
of  the  fluids  of  the  huma,n  body  as  exceeding  that  of  the  solids  by  six 
or  seven  times. 

150.  There  is  a  great  variation  in  this  respect,  however,  among  dif- 
ferent tribes  of  living  beings.  There  are  probably  no  highly  organized 
Animals,  whose  texture  contains  less  liquid  than  that  of  Yertebrata 
(unless,  it  may  be,  certain  Beetles);  but  there  can  be  no  question  that, 
among  some  of  the  Zoophytes,  the  proportion  of  solids  to  liquids  is  just 
the  other  way.  In  those  massive  coral-forming  animals,  which  seem  to 
have  been  expressly  created  for  the  purpose  of  uprearing  islands  and 
even  continents  from  the  depth  of  the  ocean,  we  find  the  soft  tissues 
confined  to  the  surface,  and  all  within  of  a  rocky  hardness.  It  is  not, 
however,  correct  to  say  (as  is  commonly  done),  that  the  coral-polypes 
"  build  up"  these  stony  structures  as  habitations  for  themselves ;  for  the 
stony  matter  is  deposited,  by  an  act  of  nutrition,  in  the  living  tissue  of 
these  animals,  just  as  much  as  it  is  in  the  bones  of  Man.  But  the  parts 
once  consolidated  henceforth  remains  dead,  so  far  as  the  animal  is  con- 
cerned ;  they  are  not  connected  with  the  living  tissues  by  any  vessels, 
nerves,  &c.,  their  density  prevents  them  from  undergoing  any  but  a  very 
slow  disintegrating  change,  so  that  they  require  and  receive  no  nutrient 
materials  ;  and  they  might  be  altogether  removed,  by  accident  or  decay, 
without  any  direct  injury  to  the  still-active,  because  yet  unconsolidated, 
portions  of  the  polype  structure. 

151.  There  is  a  close  correspondence,  in  this  respect,  between  the 
condition  of  the  stony  or  horny  stem  of  a  Coral,  and  the  heart-wood  of 
the  trunk  of  a  Tree ;  for  the  latter,  becoming  consolidated  by  internal 
deposit,  for  the  purpose  of  afi'ording  mechanical  support,  is  thenceforth  I 
totally  unconnected  with  the  vegetative  operations  of  the  tree,  and  might 
be  removed  (as  it  frequently  is  by  natural  decay)  without  afi'ecting  them. 
In  all  the  parts,  in  which  the  nutrient  processes  are  actively  going  on, 
do  we  observe  that  the  tissue  contains  a  large  proportion  of  water  ;  afid 


OF   MOISTURE   AS   A   CONDITION    OF   VITAL   ACTIVITY.  99 

that,  if  the  succulent  portions  be  dried  up,  their  vital  properties  are  de- 
stroyed. Thus  it  is  in  the  soft  tissue  at  the  extremities  of  the  radicles 
or  root-fibres,  that  the  function  of  absorption  takes  place  with  the 
greatest  activity ;  so  that  these  parts  have  received  the  name  of  spon- 
gioles:  it  is  in  the  cells  which  form  the  soft  parenchyma  of  the  leaves, 
that  the  elaboration  of  the  sap  takes  place,  the  fixation  of  carbon  frora- 
the  atmosphere,  and  the  preparation  of  the  peculiar  secretions  of  the 
plant :  and  it  is  in  the  space  between  the  bark  and  the  wood,  which  is 
occupied  (at  the  season  of  most  active  growth)  by  a  saccharine  glutinous 
fluid,  that  the  formation  of  the  new  layers  of  wood  and  bark  takes  place. 
Now,  as  soon  as  these  parts  become  consolidated,  they  cease  to  perform 
any  active  vital  operations.  The  &pongioles,  by  the  lengthening  of  the 
root-fibres,  become  converted  into  a  portion  of  those  fibres,  and  remain 
subservient  merely  to  the  transmission  of  the  fluids  absorbed;  the  leaves 
gradually  become  choked  by  the  saline  and  earthy  particles  contained 
in  the  ascending  sap,  which  they  have  had  no  power  of  excreting,  and 
they  wither,  die,  and  fall  off;  and  the  new  layers  of  wood  and  bark, 
when  once  formed,  undergo  but  little  further  change,  and  are  subser- 
vient to  little  else  than  the  transmission  of  the  ascending  and  descending 
sap  to  the  parts  where  they  are  to  be  respectively  appropriated. 

152.  There  are  some  remarkable  instances  in  both  the  Animal  and 
Vegetable  kingdoms,  of  an  immense  preponderance  in  the  amount  of 
the  fluids  over  that  of  the  solids  of  the  structure.  This  is  characteristic 
of  the  whole  class  of  Acalephce  or  Jelly-Fish^  giving  to  their  tissues  that 
softness  from  which  their  common  name  is  derived ;  these  animals,  in 
consequence,  are  unable  to  live  out  of  water ;  for  when  they  are  removed 
from  it,  a  drain  of  their  fluids  commences,  which  soon  reduces  their 
weight  to  a  degree  that  destroys  their  lives, — a  Medusa  weighing  fifty 
pounds  being  thus  dried  down  to  a  weight  of  as  many  grains.  The  most 
remarkable  instances  of  a  parallel  kind  among  Plants,  are  to  be  found 
in  the  tribe  of  Fungi ;  certain  members  of  which  are  distinguished  by 
an  almost  equally  small  proportion  of  solid  materials  in  their  textures, 
presenting  a  most  delicate  gossamer-like  appearance  to  the  eye,  and 
possessing  such  little  durability,  that  they  come  to  maturity  and  undergo 
decay  in  the  course  of  a  few  hours.  These  are  not  inhabitants  of  the 
water,  but  will  vegetate  only  in  a  very  damp  atmosphere. 

153.  As  we  find  various  Plants  and  Animals  very  differently  con- 
structed, in  regard  to  the  amount  of  fluid  contained  in  their  tissues,  so 
do  we  also  find  them  dependent  in  very  different  degrees  upon  a  con- 
stant supply  of  external  moisture.  There  is  no  relation,  however,  be- 
tween the  succulence  of  a  plant,  and  the  degree  of  its  dependence  upon 
water ;  in.  fact,  we  commonly  find  the  most  succulent  plants  growing  in 
the  driest  situations ;  whilst  the  plants,  which  are  adapted  to  localities 
where  they  can  obtain  a  constant  supply  of  fluid,  are  not  usually  re- 
markable for  the  amount  of  water  in  their  own  structure.  This,  how- 
ever, is  easily  explained.  We  find  the  most  succulent  plants, — such 
as  the  Sedums  or  Stone-crops  of  our  own  country,  and  the  Cacti  and 
Uuphorbice  of  the  tropics, — in  dry  exposed  situations,  where  they  seem 
as  if  they  would  be  utterly  destitute  of  nutriment.  The  fact  is,  how- 
ever, that  they  lose  their  fluid  by  exhalation  very  slowly,  in  consequence 


1"#0  EXTERNAL   CONDITIONS   OF   VITAL   ACTIVITY. 

of  their  small  number  of  stomata  ;  whilst,  on  the  other  hand,  they  absorb 
with  great  readiness  during  rainy  weather,  and  are  enabled,  by  the 
fleshiness  of  their  substance,  to  store  up  a  large  quantity  of  moisture 
until  it  is  required.  In  some  parts  of  Mexico,  the  heat  is  so  intense, 
and  the  soil  and  atmosphere  so  dry,  during  a  large  part  of  the  year, 
that  no  vegetation  is  found  at  certain  seasons,  save  a  species  of  Cactus ; 
this  affords  a  wholesome  and  refreshing  article  of  food,  on  which  travel- 
lers have  been  able  to  subsist  for  many  days  together,  and  without 
which  these  tracts  would  form  impassable  barriers.  On  the  othei*  hand, 
the  plants  of  damp  situations  usually  exhale  moisture  almost  as  fast  as 
they  imbibe  it ;  and  consequently,  if  their  usual  supply  be  cut  off  or 
diminished,  they  soon  wither  and  die.  Plants  that  usually  live  entirely 
submerged,  are  destitute  of  the  cuticle  or  thin  skin,  which  covers  the 
surface  in  other  cases ;  in  consequence  of  this,  they  very  rapidly  lose 
their  fluid,  when  they  are  removed  from  the  water ;  and  they  are  hence 
dependent  upon  constant  immersion  in  it  for  the  continuance  of  their 
lives,  although  their  tissues  may  not  be  remarkable  for  the  amount  of 
fluid  which  they  contain. 

154.  There  are  some  Plants  which  are  capable  of  adapting  themselves 
to  a  great  variety  of  situations,  difi'ering  widely  as  to  the  amount  of 
moisture  which  their  inhabitants  can  derive  from  the  soil  and  atmo- 
sphere ;  and  we  may  generally  notice  a  marked  difi'erence  in  the  mode 
of  growth,  when  we  compare  individuals  that  have  grown  under  oppo- 
site circumstances.  Thus  a  plant  from  a  dry  exposed  situation,  shall 
be  stunted  and  hairy,  whilst  another,  of  the  same  species,  but  developed 
in  a  damp  sheltered  situation,  shall  be  rank  and  glabrous  (smooth). 
But  in  general  there  is  a  certain  quantity  of  moisture  congenial  to  each 
species;  and  the  excess  or  deficiency  of  this  condition  has,  in  conse- 
quence, as  great  an  influence  in  determining  the  geographical  distribu- 
tion of  Plants,  as  the  amount  of  light  and  heat.  Thus,  as  already 
remarked,  the  Orchidege  and  Tree  Ferns  of  the  tropics  grow  best  in  an 
atmosphere  loaded  with  dampness ;  whilst  the  Cactus  tribe,  for  the  most 
part,  flourishes  best  in  dry  situations.  The  former  become  stunted  and 
inactive,  if  limited  in  their  supply  of  aerial  moisture ;  whilst  the  latter, 
if  too  copiously  nourished,  become  dropsical  and  liable  to  rot.  Among 
the  plants  of  our  own  country,  we  find  a  similar  limitation ;  a  moist 
boggy  situation  being  indispensable  to  the  growth  of  some,  whilst  a  dry 
exposed  elevation  is  equally  essential  to  the  healthy  development  of 
others.  There  is  a  beautiful  species  of  exotic  Fern,  the  Trichomanes 
speciosum;  the  rearing  of  which  has  been  frequently  attempted  in  this 
country  and  elsewhere,  without  success ;  but  which  only  requires  an 
atmosphere  saturated  with  dampness,  for  its  healthy  development,  being 
easily  reared  in  one  of  Mr.  Ward's  closed  glass-cases.  In  this,  as  in 
similar  examples,  it  is  only  necessary  to  imitate  as  closely  as  possible 
the  conditions  under  which  the  species  naturally  grows ;  and  sometimes 
this  can  only  be  accomplished,  by  surrounding  the  plant  with  small 
trees  and  shrubs,  so  as  to  give  it  a  moister  atmosphere  than  it  could 
otherwise  attain.  Professor  Royle  mentions  the  growth,  under  stich 
circumstances,  of  a  fine  specimen  of  the  Xanthochymus  dulcisy  one  of 
the  Gruttiferce  or  Gamboge-trees,  in  the  garden  of  the  King  of  Delhi ; 


OF   MOISTURE  AS   A   CONDITION   OF   VITAL  ACTIVITY.  101 

this  tree  is  naturally  found  only  in  the  southern  parts  of  India ;  and  the 
success  of  its  cultivation  in  this  northerly  situation  is  entirely  due  to 
its  being  sheltered  by  the  numerous  buildings  within  the  lofty  palace 
wall,  surrounded  by  almost  a  forest  of  trees,  and  receiving  the  benefit 
of  perpetual  irrigation  from  a  branch  of  the  canal  wjiich  flows  through 
the  garden. 

155.  In  regard  to  the  influence  of  external  moisture  upon  Animal 
life,  there  is  much  less  to  be  said ;  since  the  mode  in  which  fluid  is  re- 
ceived into  the  system  is  so  entirely  diff'erent.  It  may  be  remarked, 
however,  that  Animals  habitually  living  beneath  the  water,  like  sub- 
merged Plants,  are  usually  incapable  of  sustaining  life  for  any  length 
of  time  when  removed  from  it,  in  consequence  of  the  rapid  loss  of  fluid 
which  they  undergo  from  their  surface.  It  is,  however,  by  the  desic- 
cation of  the  re^'piratory  surface,  preventing  the  due  aeration  of  the 
blood,  that  the  final  result  is  for  the  most  part  occasioned ;  since  we 
find  that  when  there  is  a  special  provision  to  prevent  this,  as  in  the 
case  of  certain  Fishes  and  Crustacea,  the  animals  can  quit  the  water 
for  a  great  length  of  time.  There  can  be  no  doubt  that  the  amount  of 
Atmospheric  moisture  is  one  of  those  conditions,  which  are  collectively 
termed  climate,  and  which  influence  the  geographical  distribution  of 
Animals,  no  less  than  that  of  Plants.  But  it  is  difficult  to  say  how  far 
the  variations  in  moisture  act  alone.  There  can  be  no  doubt,  however, 
of  their  operation ;  for  every  one  is  conscious  of  the  efi'ect,  upon  his 
health  and  spirits,  of  such  variations  as  take  place  in  the  climate  he 
may  inhabit.  The  two  principal  modes  in  which  these  will  operate,  will 
be  by  accelerating  or  checking  the  exhalation  of  fluid  from  the  skin  and 
from  the  pulmonary  surface;  for  when  the  air  is  already  loaded  with 
dampness,  the  exhaled  moisture  cannot  be  carried  off  with  the  same 
readiness  as  when  it  is  in  a  condition  of  greater  dryness ;  and  it  will 
consequently  either  remain  within  the  system,  or  it  will  accumulate  and 
form  sensible  perspiration. 

156.  Now  each  of  these  states  may  be  salutary,  being  the  one  best 
adapted  to  particular  constitutions,  or  to  different  states  of  the  same 
individual.  A  cold  drying  wind  shall  be  felt  as  invigorating  to  the 
relaxed  frame  as  it  is  chilling  to  one  that  has  no  warmth  or  moisture  to 
spare;  on  the  other  hand,  a  warm  damp  atmosphere,  which  is  refresh- 
ing to  the  latter,  shall  be  most  depressing  to  the  former.  All  who  have 
tried  the  effect  of  closely-fitting  garments,  impervious  to  njoisture,  are 
well  aware  how  oppressive  they  soon  become ;  this  feeling  being  de- 
pendent upon  the  obstruction  they  occasion  to  the  act  of  perspiration, 
by  causing  the  included  air  to  be  speedily  saturated  with  moisture. 
When  the  fluids  of  the  system  have  been  diminished  in  amount,  either 
by  the  suspension  of  a  due  supply  of  water,  or  by  an  increase  in  the 
excretions,  there  is  a  peculiar  refreshment  in  a  soft  damp  atmosphere, 
or  in  a  warm  bath,  which  allows  the  loss  to  be  replaced  by  absorption 
through  the  general  cutaneous  surface.  The  reality  of  such  absorption 
has  been  placed  beyond  all  doubt,  by  observations  upon  men,  who  had 
been  exposed  to  a  hot  dry  air  for  some  time,  and  afterwards  placed  in 
a  warm  bath ;  for  it  was  found  that  the  system  would  by  this  unusual 


102  EXTERNAL   CONDITIONS    OF   VITAL   ACTIVITY. 

means  supply  the  deficiency,  which  had  been  created  by  the  previous 
increase  in  the  transpiration. 

157.  The  effect  of  a  moist  or  dry  atmosphere,  then,  upon  the  Animal 
body,  cannot  be  by  any  means  unimportant;  although,  as  we  shall 
hereafter  see,  there  exists  in  it  a  series  of  the  most  remarkable  provi- 
sions for  regulating  the  amount  of  its  fluids.  The  influence  of  atmo- 
spheric moisture,  however,  is  most  obvious  in  disordered  states  of  the 
system.  Thus  in  persons  who  are  subject  to  the  form  of  Dyspepsia 
called  atonic,  which  is  usually  connected  with  a  generally-relaxed  con- 
dition of  the  system,  a  very  perceptible  influence  is  experienced  from 
changes-  in  the  quantity  of  atmospheric  moisture ;  the  digestive  power, 
as  well  as  the  general  functions  of  the  body,  being  invigorated  by  dry- 
ness, and  depressed  by  damp.  Again  there  is  no  doubt  that,  where  a 
predisposition  exists  to  the  Tuberculous  Cachexia,  it  is  greatly  favoured 
by  habitual  exposure  to  a  damp  atmosphere,  especially  when  accom- 
panied by  cold :  indeed  it  would  appear,  from  the  influence  of  cold  damp 
situations  upon  animals  brought  from  warmer  climates,  that  these  two 
causes  may  induce  the  disease,  in  individuals  previously  healthy.  On 
the  other  hand,  there  are  some  forms  of  pulmonary  complaints,  in  which 
an  irritable  state  of  the  mucous  membrane  of  the  bronchial  tubes  has  a 
large  share ;  when  this  irritation  presents  itself  in  the  dry  form,  a  warm 
moist  atmosphere  is  found  most  soothing  to  it ;  whilst  a  drier  and  more 
bracing  air  is  much  more  beneficial,  when  the  irritation  is  accompanied 
by  a  too  copious  secretion. 

158.  Although,  as  already  stated,  no  .vital  actions  can  go  on  without 
a  reaction  between  the  solids  and  fluids  of  the  body,  yet  there  may  be 
an  entire  loss  of  the  latter,  in  certain  cases,  without  necessarily  destroy- 
ing life ;  the  structure  being  reduced  to  a  state  of  dormant  vitality,  in 
which  it  may  remain  unchanged  for  an  unlimited  period ;  and  yet  being 
capable  of  renewing  all  its  actions,  when  moisture  is  again  supplied.  Of 
this  we  find  numerous  examples  among  both  the  Vegetable  and  the  Ani- 
ilial  kingdoms.  Thus  the  Mosses  and  Liverworts,  which  inhabit  situa- 
tions where  they  are  liable  to  occasional  drought,  do  not  suffer  from 
being,  to  all  appearance,  completely  dried  up;  but  revive  and  vegetate 
actively,  as  soon  as  they  have  been  thoroughly  moistened.  Instances 
are  recorded,  in  which  Mosses  that  have  been  for  many  years  dried  up 
in  an  Herbarium,  have  been  restored  by  moisture  to  active  life.  There 
is  a  Lycopodium  (Club-Moss)  inhabiting  Peru,  which,  when  dried  up  for 
want  of  moisture,  folds  its  leaves  and  contracts  into  a  ball ;  and  in  this 
state,  apparently  quite  devoid  of  animation,  it  is  blown  hither  and  thither  ' 
along  the  surface  by  the  wind.  As  soon,  however,  as  it  reaches  a  moist 
situation,  it  sends  down  its  roots  into  the  soil,  and  unfolds  to  the  atmo- 
sphere its  leaves,  which,  from  a  dingy  brown,  speedily  change  to  the  i 
bright  green  of  active  vegetation.  The  Anastatica  (Rose  of  Jericho)  is 
the  subject  of  similar  transformations ;  contracting  into  a  ball,  when 
dried  up  by  the  burning  sun  and  parching  air ;  being  detached  by  the 
wind  from  the  spot  where  its  slender  roots  had  fixed  it,  and  rolled  over 
the  plains  to  indefinite  distances ;  and  then,  when  exposed  to  moisture, 
unfolding  its  leaves,  and  opening  its  rose-like  flower,  as  if  roused  from 
sleep.     A  blue  Water-Lily  abounds  in  several  of  the  canals  at  Alexan- 


OF   MOISTURE  AS   A   CONDITION  OF  VITAL   ACTIVITY.  103 

dria,  which  at  certain  seasons  become  so  dry,  that  their  beds  are  burnt 
as  hard  as  bricks  by  the  action  of  the  sun,  so  as  to  be  fit  for  use  as  car- 
riage roads  ;  yet  the  plants  do  not  thereby  lose  their  vitality;  for  when 
the  water  is  again  admitted,  they  resume  their  growth  with  redoubled 
vigour. 

159.  Among  the  lower  Animals,  we  find  several  of  considerable  com- 
plexity of  structure,  which  are  able  to  sustain  the  most  complete  desic- 
cation. This  is  most  remarkably  the  case  in  the  common  Wheel-Ani- 
malcule; which  may  be  reduced  to  a  state  of  most  complete  dryness, 
and  kept  in  this  condition  for  any  length  of  time,  and  which  will  yet 
revive  immediately  on  being  moistened.  The  same  individuals  may  be 
treated  in  this  manner,  over  and  over  again.  Experiments  have  been 
carried  still  further  with  the  allied  tribe  of  Tardigrades ;  individuals  of 
which  have  been  kept  in  a  vacuum  for  thirty  days,  with  sulphuric  acid 
and  Chloride  of  Calcium  (thus  sufi'ering  the  most  complete  desiccation 
the  Chemist  can  effect),  and  yet  have  not  lost  their  vitality.  It  is  sin- 
gular that  in  this  desiccated  condition,  they  may  be  heated  to  a  tem- 
perature of  250°,  without  the  destruction  of  their  vitality ;  although, 
when  in  full  activity,  they  will  not  sustain  a  temperature  of  more  than 
from  112°  to  115°.  Some  of  the  minute  Entomostracous  Crustacea, 
which  are  nearly  allied  to  the  Rotifera,  appear  to  partake  with  them  in 
this  curious  faculty.  Many  instances  are  on  record  in  which  Snails 
and  other  terrestrial  Mollusca  have  revived,  after  what  appeared  to  be 
complete  desiccation ;  and  the  eggs  of  the  Slug,  when  dried  up  by  the 
sun  or  by  artificial  heat,  and  reduced  to  minute  points  only  visible  with 
the  Microscope,  are  found  not  to  have  lost  their  fertility,  when  they  are 
moistened  by  a  shower  of  rain,  or  by  immersion  in  water,  which  restores 
them  to  their  former  plumpness.  Even  after  being  treated  eight  times 
in  this  manner,  the  eggs  were  hatched  when  placed  in  favourable  cir- 
cumstances ;  and  even  eggs  in  which  the  embryo  was  distinctly  formed, 
survived  such  treatment  without  damage. — That  such  capability  should 
exist  in  the  animals  and  eggs  just  mentioned,  shows  a  remarkable  adap- 
tation to  the  circumstances  in  which  they  are  destined  to  exist ;  since 
were  it  not  for  their  power  of  surviving  desiccation,  the  races  of  Wheel- 
Animalcules  and  Entomostraca  must  speedily  become  extinct,  through 
the  periodical  drying  up  of  the  small  collections  of  water  which  they 
inhabit ;  and  a  season  of  prolonged  drought  must  be  equally  fatal  to 
the  terrestrial  Mollusca. 

160.  It  would  seem  that  many  cold-blooded  animals  are  reduced,  by 
a  moderate  deficiency  of  fluid,  to  a  state  of  torpidity  closely  resembling 
that  induced  by  cold ;  and  hence  it  is,  that  during  the  hottest  and  driest 
part  of  the  tropical  year,  there  is  almost  as  complete  an  inactivity  as  in 
the  winter  of  temperate  regions.  The  common  Snail,  if  put  into  a  box 
without  food,  constructs  a  thin  operculum  or  partition  across  the  orifice 
of  the  shell,  and  attaches  itself  to  the  side  of  the  box :  in  this  state  it 
may  remain  dormant  for  years,  without  being  affected  by  any  ordinary 
changes  of  temperature  :  but  it  will  speedily  revive  if  plunged  in  water. 
Even  in  their  natural  haunts,  the  terrestrial  Mollusca  of  our  own  cli- 
mates are  often  found  in  this  state  during  the  summer,  when  there  is  a 
continued  drought;  but  with  the  first  shower  they  revive  and  move 


L 


104  EXTERNAL   CONDITIONS   OF  VITAL   ACTIVITY. 

about.  In  like  manner  it  is  observed  that  the  rainy  season,  between 
the  tropics,  brings  forth  the  hosts  of  insects,  which  the  drought  had 
caused  to  remain  inactive  in  their  hiding-places.  Animals  thus  rendered 
torpid  seem  to  have  a  tendency  to  bury  themselves  in  the  ground,  like 
those  which  are  driven  to  winter  quarters  by  cold.  Mr.  Darwin  men- 
tions that  he  observed  with  some  surprise  at  Rio  de  Janeiro,  that,  a  few 
days  after  some  little  depressions  had  been  changed  into  pools  of  water 
by  the  rain,  they  were  peopled  by  numerous  full-grown  shells  and  beetles. 
161.  This  torpidity  consequent  upon  drought  is  not  confined  to  In- 
vertebrated  animals.  There  are  several  Fish,  inhabiting  fresh  water, 
which  bury  themselves  in  the  mud  when  their  streams  or  pools  are  dried 
up,  and  which  remain  there  in  a  torpid  condition  until  they  are  again 
moistened.  This  is  the  case  with  the  curious  Lepidosiren,  which  forms 
so  remarkable  a  connecting  link  between  Fishes  and  the  Batrachian  Rep- 
tiles :  it  is  an  inhabitant  of  the  upper  parts  of  the  river  Gambia,  which 
are  liable  to  be  dried  up  during  much  more  than  half  the  year;  and  the 
whole  of  this  period  is  spent  by  it  in  a  hollow  which  it  excavates  for 
itself  deep  in  the  mud,  where  it  lies  coiled  up  in  a  completely  torpid 
condition, — whence  it  is  called  by  the  natives  the  sleeping-fish.  When 
the  return  of  the  rainy  season  causes  the  streams  to  be  again  filled,  so 
that  the  water  finds  its  way  down  to  the  hiding-place  of  the  Lepidosiren, 
it  comes  forth  again  for  its  brief  period  of  activity ;  and  with  the-  ap- 
proach of  drought,  it  again  works  its  way  down  into  the  mud,  which 
speedily  hardens  around  it  into  a  solid  mass.  In  the  same  manner,  the 
ProteuSj  an  inhabitant  of  certain  lakes  in  the  Tyrol,  which  are  liable  to 
be  periodically  dried  up,  retires  at  these  periods  to  the  underground  pas- 
sages that  connect  them,  where  it  is  believed  to  remain  in  a  torpid  con- 
dition ;  and  it  thence  emerges  into  the  lakes,  as  soon  as  they  again  be- 
come filled  with  water.  The  Lizards  and  Serpents,  too,  of  tropical 
climates  appear  to  be  subject  to  the  same  kind  of  torpidity,  in  conse- 
quence of  drought,  as  that  which  aff"ects  those  of  temperate  regions 
during  the  cold  of  winter.  Thus  Humboldt  has  related  the  strange  acci- 
dent of  a  hovel  having  been  built  over  a  spot  where  a  young  Crocodile 
lay  buried  alive,  though  torpid,  in  the  hardened  mud;  and  he  mentions 
that  the  Indians  often  find  enormous  Boas  in  the  same  lethargic  state ; 
and  that  these  revive  when  irritated  or  wetted  with  water.  All  these 
examples  show  the  necessity  of  a  fixed  amount  of  fluid,  in  the  animal 
structure,  for  the  maintenance  of  vital  activity :  whilst  they  also  demon- 
strate, that  the  preservation  of  the  vital  properties  of  that  structure  is  , 
not  always  incompatible  with  the  partial,  or  even  the  complete  abstrac- 
tion of  that  fluid ;  the  solid  portions  being  then  much  less  liable  to  de- 
composition than  by  heat,  or  by  other  agencies,  than  they  are  in  their 
ordinary  condition. 


ELEMENTARY   PARTS   OF   ANIMAL   STRUCTURES.  105 

CHAPTER  III. 

OF  THE  ELEMENTARY  PARTS  OF  ANIMAL  STRUCTURES. 

162.  In  the  investigation  of  the  operations  of  a  complex  piece  of  Me- 
chanism, and  in  the  study  of  the  forces  which  combine  to  produce  the 
general  result,  experience  shows  the  advantage  of  first  examining  the 
component  parts  of  the  Machine, — its  springs,  wheels,  levers,  cords, 
pulleys,  &c., — determining  the  properties  of  their  materials,  and  ascer- 
taining their  individual  actions.  When  these  have  been  completely 
mastered,  the  attention  may  be  directed  to  their  combined  actions :  and 
the  bearing  of  these  combinations  upon  each  other,  so  as  to  produce  the 
general  result,  would  be  the  last  object  of  study. 

163.  This  seems  the  plan  which  the  Student  of  Physiology  may  most 
advantageously  pursue,  in  the  diflScult  task  of  making  himself  acquainted 
with  the  operations  of  the  living  Organism,  and  with  the  mode  in  which 
they  concur  in  the  maintenance  of  Life.  He  should  first  examine  the 
properties  of  the  component  materials  of  the  structure,  in  their  simplest 
form :  these  he  will  find  in  its  nutrient  fluids.  He  may  next  proceed  to 
the  simplest  forms  of  organized  tissue,  which  result  from  the  mere  solidi- 
fication of  those  materials,  and  whose  properties  are  chiefly  of  a  mechani- 
cal nature.  From  these  he  will  pass  to  the  consideration  of  the  struc- 
ture and  actions  of  those  tissues  that  consist  chiefly  of  cells;  and  will 
investigate  the  share  they  take  in  the  strictly  vital  operations  of  the 
economy.  Next  his  attention  will  be  engaged  by  the  tissues  produced 
by  the  transformation  of  cells ;  of  which  some  are  destined  chiefly  for 
affording  mechanical  support  to  the  fabric,  and  others  for  peculiar  vital 
operations.  And  he  will  be  tljen  prepared  to  understand  the  part  which 
these  elementary  tissues  severally  perform  in  the  more  complex  organs. 
A  due  knowledge  of  these  elementary  parts,  and  of  their  physical,  chemi- 
cal, and  vital  properties,  is  essential  to  every  one  who  aims  at  a  scientific 
knowledge  of  Physiology.  True  it  is,  that  we  may  study  the  results  of 
their  operations,  without  acquaintance  with  them ;  but  we  should  know 
nothing  more  of  the  working  of  the  machine,  than  we  should  know  of 
a  cotton-mill,  into  which  we  saw  cotton-wool  entering,  and  from  which 
we  saw  woven  fabrics  issuing  forth  ;  or  of  a  paper-making-machine,  which 
we  saw  fed  at  one  end  with  rags,  and  discharging  hot-pressed  paper,  cut 
into  sheets,  at  the  other.  The  study  of  these  results  affords,  of  course, 
a  very  important  part  of  the  knowledge  we  have  to  acquire  respecting 
the  operations  of  the  machine ;  but  we  could  learn  from  them  very  little 
of  the  nature  of  the  separate  processes  effected  by  it;  still  less  should 
we  be  prepared,  by  any  disorder  or  irregularity  in  the  general  results,  to 
seek  for,  and  rectify,  the  cause  of  that  disturbance  in  the  working  of  the 
machine,  by  which  the  abnormal  result  was  occasioned. 

164.  Now  just  as  in  a  cotton-mill,  there  are  machines  of  several 
different  kinds,  adapted  to  effect  different  steps  of  the  process  by  which 
the  raw  material  is  converted  into  the  woven  fabric,  so  do  we  find  that 
in  the  complex  Animal  fabric  there  is  a  great  variety  of  organs  for  per- 


L 


106  ELEMENTARY   PARTS   OF  ANIMAL   STRUCTURES. 

forming  the  several  changes,  by  which  the  fabric  itself  is  built  up  and 
maintained  in  a  condition  fit  for  the  performance  of  its  peculiar  opera- 
tions. These  operations  are  the  phenomena  of  sensation,  of  spontaneous 
motion,  and  of  mental  action.  They  are  the  great  objects  of  Animal 
existence ;  just  as  the  combination  of  elements  into  organic  substances, 
that  are  to  furnish  the  materials  of  the  Animal  fabric,  seems  to  be  the 
great  purpose  of  Vegetative  Life.  The  vital  phenomena  which  are 
peculiar  to  Animals,  are  manifestations  of  the  properties  of  certain  forms 
of  organized  matter, — the  Nervous  and  Muscular  tissues, — which  are 
restricted  to  themselves ;  just  as  those  Avhich  are  common  to  Animals 
and  Plants,  are  effected  by  organized  structures  which  are  found  alike 
in  both  kingdoms.  Here,  then,  we  have  one  essential  distinction  between 
these  kingdoms  ; — namely,  the  presence  in  Animals  of  a  peculiar  appa- 
ratus, and  the  consequent  possession  by  them  of  peculiar  endowments, 
which  are  totally  wanting  in  Plants.  There  are,  it  is  true,  many  species, 
indeed  whole  tribes,  in  which  it  is  impossible  to  say  with  certainty,  how 
far  sensibility  and  spontaneity  of  action  may  be  justly  inferred  from  the 
movements  they  exhibit ;  so  that,  their  structure  being  so  simple  as  to 
afford  no  distinctive  characters,  our  assignment  of  them  to  the  Animal 
or  to  the  Vegetable  kingdom  must  be  determined  entirely  by  the  mode 
in  which  they  obtain  the  materials  of  their  nutrition  (§§  62,  63). 

165.  All  the  operations,  then,  which  are  common  to  Animals  and 
Plants,  are  concerned  in  the  building  up  of  the  organized  fabric,  in  the 
maintenance  of  its  integrity,  and  in  the  preparation  of  the  germs  of  new 
structures,  to  compensate  for  the  loss  of  the  parent  by  death.  These 
operations,  as  formerly  explained  (§41),  involve  a  series  of  very  distinct 
processes  ;  which,  though  all  performed  by  the  simple  cell  of  the  humblest 
plant,  are  distributed  in  more  complex  structures  through  a  number  of 
parts  or  organs,  whose  several  actions  are  almost  as  separate  as  those 
of  the  dissimilar  machines  of  the  cotton-mill, — although,  like  them,  sus- 
tained by  the  same  powers,  and  so  far  mutually  dependent,  that  neither 
of  them  can  be  suspended  without  in  a  short  time  putting  a  stop  to  thei 
rest.  Now  just  as  in  each  of  the  machines  of  the  cotton-mill  we  may 
have  similar  elements, — such  as  wheels,  levers,  pulleys,  bands,  &c.,  put 
together  in  different  methods,  and  consequently  adapted  for  different  pur- 
poses, as  carding,  spinning,  weaving,  &c.,  so  shall  we  find  in  the  animal 
body,  that  these  different  organs  are  composed  of  very  similar  elements, 
and  that  the  individual  actions  of  these  elementary  parts  are  the  same; 
but  that  the  difference  of  result  is  the  consequence  of  the  variety  in  their 
arrangement.  Thus  we  shall  find  that  the  growth  of  cells,  their  absorp- 
tion of  certain  matters  from  the  surrounding  fluids,  and  their  subsequent 
liberation  of  these  by  the  bursting  or  liquefying  of  the  cell-wall  when 
their  term  of  life  is  come  to  an  end,  are  means  employed  in  one  part  of 
the  body  to  introduce  nutrient  materials  into  the  current  of  the  circu- 
lation, whilst  in  another  the  same  processes  are  used  as  means  to  with- 
draw, from  that  very  same  current,  certain  substances  of  which  it  is 
necessary  to  get  rid.  Now  certain  combinations  of  elementary  struc- 
ture, adapted  to  the  performance  of  a  set  of  actions  tending  to  one  pur- 
pose, and  thus  resembling  one  of  the  machines  of  a  cotton -mill,  is  termed 
an  organ  ;  and  the  sum-total  of  its  actions  is  termed  its  function.    Thus 


ALBUMINOUS  COMPOUNDS.  107 

we  have  in  the  function  of  Respiration,  which  essentially  consists  of  an 
interchange  of  oxygen  and  carbonic  acid  between  the  air  and  the  blood, 
a  multitude  of  distinct  changes,  some  of  them  of  a  character  apparently 
not  in  the  least  related  to  it,  but  all  necessary,  in  the  higher  and  more 
complex  fabric,  to  bring  the  blood  and  the  air  into  the  necessary  relation. 
The  sum-total  of  these  changes  constitutes  the  function  of  Respiration-^ 
and  the  structures  by  which  they  are  effected  are  organs  of  Respiration. 

166.  The  entire  Organized  structure,  then,  may  be  regarded  as  made 
up  of  distinct  organs,  having  their  several  and  (to  a  certain  extent) 
independent  purposes ;  and  these  organs  may  be  resolved,  in  like  man- 
ner, into  simple  elementary  parts,  whose  structure  and  composition  are 
the  same,  in  whatever  part  of  the  fabric  they  occur.  And  in  like  man- 
ner, the  phenomena  of  Life,  considered  as  a  whole,  may  be  arranged 
under  several  groups  or  functions,  according  to  the  immediate  purpose 
to  which  they  are  directed ;  and  yet  in  every  one  of  these  groups,  we 
shall  find  repeated  the  same  elementary  changes  which  are  concerned 
in  the  rest.  Thus  in  the  act  of  Respiration,  the  same  kind  of  muscular 
movements,  the  same  sort  of  nervous  agency,  are  concerned,  as  con- 
tribute to  the  ingestion  of  the  food ;  together  with  a  circulation  of 
blood,  similar  to  that  which  supplies  the  materials  for  the  nutrition  of 
the  tissues.  Hence  we  see  the  propriety  of  applying  ourselves  first  to 
the  consideration  of  the  elementary  parts  of  the  living  structure,  and  of 
the  properties  by  which  they  effect  the  changes,  that  are  characteristic 
of  its  several  organs. 

1.    Of  the  Primary  Components  of  the  Animal  Fabric. 

167.  As  we  can  best  study  the  primary  components  of  the  Animal 
fabric,  by  investigating  their  properties  before  the  process  of  Organiza- 
tion begins,  or  whilst  it  is  taking  place,  we  must  have  recourse  for  this 
purpose  to  the  nutrient  fluid, — the  Rlood,— in  which  these  are  contained 
in  the  state  most  completely  prepared  for  the  reception  of  the  vitalizing 
influence.  The  same  substances  may  be  found,  in  an  earlier  stage  of 
preparation,  in  the  Chyle  and  Lymph ;  and  also  in  the  Eggs  of  ovipa- 
rous animals.  The  circumstances  attending  the  development  of  the 
latter  afford,  indeed,  the  most  satisfactory  proof  of  the  convertibility  of 
the  simple  chemical  product.  Albumen,  with  certain  inorganic  substances, 
into  every  form  of  organized  structure.  For  the  white  of  the  egg  con- 
sists of  nothing  else  than  albumen,  combined  with  phosphate  of  lime ; 
whilst  the  yolk  is  chiefly  composed  of  the  same  substance,  mingled  with 
oily  matter,  and  a  minute  quantity  of  sulphur,  iron,  and  some  other 
inorganic  bodies.  Yet  this  albumen  and  fatty  matter  are  converted, 
after  the  lapse  of  a  few  days,  under  the  agency  of  an  elevated  tempe- 
rature upon  the  germ,  into  a  complex  fabric,  composed  of  bones,  mus- 
cles, nerves,  tendons,  ligaments,  cartilages,  fibrous  membranes,  fat, 
cellular  tissue,  &c.,  and  endowed  with  the  properties  characteristic  of 
all  these  substances,  which,  when  brought  into  consentaneous  activity, 
manifest  themselves  in  the  life  of  the  chick. — In  tracing  these  wonder- 
ful transformations,  therefore,  we  should  rightly  commence  with  Albu- 
men. 


k 


108  CHEMICAL   COMPOSITION   OF   ANIMAL   TISSUES. 

168.  Albumen  exists,  not  merely  in  the  "white  and  yolk  of  the  egg, 
but  also  in  the  various  liquids  which  supply  the  materials  for  the  nutri- 
tion of  the  Animal  tissues.  Thus  it  is  found  in  the  Chyme,  or  product 
of  the  digestive  operation,  whenever  Animal  flesh,  or  any  Vegetable 
substance  corresponding  with  it  in  composition,  has  been  taken  in  as 
food.  And  it  is  absorbed  from  the  alimentary  canal  into  the  Chyle 
and  Blood,  of  whose  solid  constituents  it  forms  a  very  large  proportion. 
In  its  soluble  state.  Albumen  is  always  combined  with  a  small  quantity 
of  free  soda,  with  which  it  seems  to  be  united  as  an  acid  with  its  base ; 
and  to  this  state  of  combination,  its  solubility  is  regarded  by  most 
Chemists  as  being  due.  When  the  fluid  in  which  it  is  dissolved  is  eva- 
porated at  a  low  temperature  (not  exceeding  126°),  the  Albumen,  or 
rather  Albuminate  of  Soda,  may  be  dried,  without  losing  its  solubility ; 
when  dried,  it  may  be  exposed  to  a  temperature  of  212°,  without  under- 
going change ;  and  it  forms,  when  again  dissolved  in  water,  the  same 
glairy,  colourless,  and  nearly  tasteless  fluid  as  before. .  When  a  higher 
temperature  is  employed,  however,  the  Albumen  passes  into  the  insolu- 
ble form  ;  and  presents  itself  either  as  a  cloudy  or  flocculent  precipitate, 
or  as  a  firm  consistent  coagulum,  according  to  the  strength  of  the  origi- 
nal solution.  The  same  condition  regulates  the  amount  of  heat  requisite 
for  the  purpose ;  thus  if  the  quantity  of  albumen  be  so  great  that  the 
liquid  has  a  slimy  aspect,  a  temperature  of  145°  or  150°  is  sufficient  for 
the  purpose,  and  the  whole  becomes  solid,  white,  and  opaque;  but  in  a 
very  dilute  condition,  boiling  is  required,  and  the  albumen  then  sepa- 
rates in  the  form  of  white  finely-divided  flocks.  In  either  case  the  soda 
and  other  soluble  salts  are  separated  from  the  albumen,  and  remain 
dissolved  in  the  water.  When  the  coagulation  of  Albumen  takes  place 
rapidly,  the  coherent  mass  seems  quite  homogeneous,  and  shows  no  trace 
of  anything  like  definite  arrangement ;  but  when  the  process  is  more 
gradual,  minute  granules  present  themselves,  which  do  not,  however, 
exhibit  a  tendency  towards  any  higher  form  of  structure.  The  insolu- 
ble coagulum,  or  pure  Albumen,  dries  up  to  a  yellow,  transparent, 
horny  substance ;  which,  when  macerated  in  water,  resumes  its  former 
whiteness  and  opacity. — Pure  Albumen  may  also  be  obtained  from  the 
solid  mass  which  remains  when  an  albuminous  fluid  is  dried  at  a  low 
temperature,  by  reducing  it  to  a  fine  powder,  and  then  washing  it  with 
cold  water  on  a  filter ;  common  salt,  with  sulphate,  phosphate,  and  car- 
bonate of  soda,  are  dissolved  out ;  and  a  soft  swollen  mass  remains  upon 
the  filter,  which  has  all  the  characters  of  Albumen  obtained  by  precipi- 
tation, except  that  it  is  readily  soluble  in  a  solution  of  nitrate  of  potash, 
■^hich  will  not  dissolve  the  latter  substance. 

169.  Albumen  may  be  thrown  down  from  its  solution,  in  a  coagulated 
state,  not  merely  by  heat,  but  by  Alcohol  and  Creasote,  and  by  most 
Acids  when  added  in  excess,  so  as  to  do  more  than  neutralize  the  alkali. 
Nitric  acid  is  particularly  efficacious  in  occasioning  its  coagulation ;  on 
the  other  hand.  Hydrochloric  and  Acetic  acids,  and  common  or  tribasic 
Phosphoric  acid,  do  not  precipitate  it,  these  acids  having  the  property 
of  dissolving  pure  Albumen.  When  albumen  is  dissolved  in  hydrochlo- 
ric acid,  a  pinkish  hue  is  at  first  seen ;  the  liquid  then  becomes  of  an 
intense  purple  colour,  and,  on  applying  heat  a  little  longer,  an  intense 


ALBUMINOUS   COMPOUNDS.  109 

blue ;  after  standing  for  some  time,  it  again  assumes  its  former  pink  or 
claret  colour. — In  the  precipitation  of  Albumen  bj  an  acid,  definite 
compounds  are  formed  between  the  two  ;  in  which  the  Albumen  acts  the 
part  of  a  base.  On  the  other  hand,  it  serves  as  an  acid  in  its  combina- 
tions with  the  caustic  alkalies,  and  is  held  in  solution  by  them.  Most 
of  the  metallic  salts,  as  those  of  Copper,  Lead,  Mercury,  &c.,  form- 
insoluble  compounds  with  albumen,  and  thus  give  precipitates  with  its 
solution ;  hence  the  value  of  white  of  egg  as  an  antidote,  in  cases  of 
poisoning  with  Corrosive  Sublimate.  The  simplest  method  of  detecting 
the  presence  of  soluble  Albumen  in  very  small  quantity,  is  to  boil  the 
liquid,  and  add  nitric  acid ;  if  turbidity  is  then  produced,  the  existence 
of  albumen  may  be  inferred.  A  more  delicate  test  of  the  presence  of 
Albumen,  however,  is  the  precipitate  which  is  given  by  the  addition  of 
the  ferro-prussiate  of  potash  to  the  liquid,  when  this  has  been  first 
acidulated  with  acetic  acid. 

170.  Albumen  is  readily  decomposed  by  the  action  of  the  fixed  alka- 
lies ;  a  disengagement  of  ammonia  being  occasioned  by  the  addition  of 
caustic  potass  to  even  a  very  weak  solution  of  albumen.  This  may  be 
made  evident  by  adding  a  solution  of  sulphate  of  copper,  a  deep  purple 
colour  being  produced  by  the  action  of  the  liberated  ammonia  upon  the 
metal ;  and  thus  the  addition  of  liquor  potassse  and  a  solution  of  sul- 
phate of  copper,  forms  a  very  delicate  test  for  the  presence  of  albumen. 
If  Albumen,  or  any  albuminous  compound,  be  heated  with  caustic 
potash,  it  is  completely  decomposed;  not,  however,  being  resolved  at 
once  into  its  ultimate  constituents,  or  altogether  into  simple  combina- 
tions of  them,  but  in  great  part  into  other  organic  compounds.  One  of 
these,  termed  Leucin,  is  a  crystalline  substance,  which  forms  colourless 
scales,  destitute  of  taste  and  odour ;  it  is  soluble  in  water  and  alcohol, 
and  sublimes  unchanged.  It  consists  of  12  Carbon,  12  Hydrogen,  1 
Nitrogen,  and  4  Oxygen.  There  is  not  at  present  any  evidence  that  it 
is  produced  in  the  living  body ;  and  the  chief  interest  which  attaches  to 
it  arises  from  the  fact,  that  it  may  be  procured  from  Gelatine  as  well 
as  from  Proteine ;  which  indicates  a  certain  relationship  between  these 
two  substances.  Another  compound  abtained  by  the  same  reaction,  is 
called  Tyrosin;  it  crystallizes  in  brilliant  needles;  and  its  composition 
is  16  C,  9  H,  1  N,  5  0. — Besides  these  substances.  Ammonia,  with 
Formic  and  Carbonic  Acids,  are  produced;  the  acids  unite  with  the 
potash  emj^loyed  to  effect  the  decomposition ;  and  the  ammonia  is  set 
free. — The  action  of  caustic  potash  upon  Albumen  has  also  the  effect 
of  liberating  sulphur,  which  unites  with  the  potash,  and  remains  in  the 
solution,  where  its  presence  may  be  recognised  by  the  black  precipitate 
formed  on  the  addition  of  a  solution  of  acetate  of  lead.  The  existence 
of  unoxidized  Sulphur  in  albumen  is  shown  by  the  familiar  fact  of  the 
blackening  of  a  silver  spoon  by  a  boiled  egg,  which  is  due  to  the  forma- 
tion of  an  alkaline  sulphuret  during  coagulation.  Albumen  may  also 
be  shown  to  contain  Phosphorus  in  an  unoxidized  state.  In  its  soluble 
state.  Albumen  is  very  commonly  united  with  Phosphate  of  Lime,  about 
two  per  cent,  of  which  may  be  taken  up  by  it ;  and  it  is  chiefly  in  this 
mode,  that  this  very  important  substance  is  introduced  into  the  Animal 
body. 


k 


I 

110  CHEMICAL   COMPOSITION   OF   ANIMAL   TISSUES. 

171.  The  ultimate  composition  of  the  Albumen  of  the  blood  may  be 
stated  as  follows  : — 

Carbon,    -            -            -            .            -  548 

Hydrogen,      -            -            -            -            -  71 

^          Oxygen,    -----  212 

Nitrogen,        -----  159 

Sulphur,  -----  7 

Phosphorus,  -----  3 

1000 

.  It  has  been  maintained  by  Mulder,  that  the  sulphur  and  phosphorus 
may  be  completely  separated  from  the  substance  formed  by  the  union 
of  the  first  four  elements ;  and  to  this  substance,  he  gave  the  name  of 
P.roteine,  believing  it  to  be  the  base  of  the  whole  series  of  albuminous 
compounds,  which  are  supposed  to  consist  of  proteine,  united  with  sul- 
phur and  phosphorus  in  varying  proportions.  It  does  not  appear,  how- 
ever, that  proteine  has  ever  been  really  obtained  in  an  isolated  form ; 
and  its  existence  must  at  present  be  considered  as  hypothetical.  It 
may  be  convenient,  however,  to  use  the  phrase  ^' proteine-compounds," 
to  designate  the  whole  series  of  Animal  and  Vegetable  substances, 
which  are  capable  of  being  converted  into  Albumen  in  the  digestive 
process :  and  in  this  sense  alone  will  it  be  here  employed. — The  atomic 
constitution  of  Proteine  is  considered  by  Liebig  to  be  represented  by 
the  formula — 

49  Carbon,  36  Hydrogen,  14  Oxygen,  6  Nitrogen. 

whilst  by  Mulder  the  following  formula  is  adopted — 

40  Carbon,  31  Hydrogen,  12  Oxygen,  5  Nitrogen.  jM 

Both  these  formulae  are  sufficiently  conformable  to  the  relative  propor- 
tions of  the  components ;  but  it  has  not  been  yet  determined  which  best 
represents  the  combining  equivalent  of  the  substance. 

172.  Nearly  allied  to  Albumen  is  the,  substance  termed  Oaseine,  i 
which  replaces  it  in  milk ;  and  this  is  specially  worthy  of  notice  here, 
because  it  is  the  sole  form  in  which  the  young  Mammal  receives  Pro- 
teine into  its  body,  during  the  period  of  lactation.  Like  Albumen,  this 
substance  may  exist  in  two  forms,  the  soluble,  and  the  insoluble  or  coa- 
gulated ;  and  it  further  agrees  with  it,  in  requiring,  as  a  condition  of 
its  solubility,  the  presence  of  a  free  alkali,  of  which,  however,  a  very 
small  quantity  suffices  for  the  purpose.  It  differs  from  Albumen,  how- 
ever, in  this :  that  it  does  not  coagulate  by  heat,  and  that  it  is  precipi- 
tated from  its  solution  by  Acetic  acid.  Caseine  is  further  remarkable 
for  the  facility  with  which  its  coagulation  is  effected  by  the  contact  of 
certain  animal  membranes,  as  in  the  ordinary  process  of  cheese-making. 
This  change  is  considered  by  some  Chemists  to  be  due,  however,  not  to 
any  direct  action  of  the  membrane  upon  the  caseine,  but  to  its  influence 
in  converting  some  of  the  milk-sugar  into  lactic  acid,  which,  separating 
the  alkali  of  the  caseine,  will  occasion  the  precipitation  of  the  latter. 
The  only  difference  which  can  be  detected  between  Albumen  and  Case- 
ine, in  regard  to  the  proportions  of  their  elements,  consists  in  the  ab-  j 
sence  of  Phosphorus,  and  the  smaller  proportion  of  Sulphur,  in  the! 
latter ;  but  this  can  scarcely  be  the  cause  of  the  foregoing  differences  in  J 


ALBUMINOUS   COMPOUNDS.  Ill 

their  properties.  Caseine  appears  even  to  surpass  Aljbumen  in  its  power 
of  combining  with  the  phosphates  of  lime  and  magnesia,  and  of  render- 
ing them  soluble. 

173.  Albumen  and  Caseine,  then,  may  be  regarded  as  constituting 
the  raw  materials,  at  the  expense  of  which  the  organized  tissues  of  the 
Animal  fabric  are  built  up ;  and  we  have  sufficient  evidence,  in  the  de-^- 
velopment  of  the  Chick  from  the  egg,  and  of  the  young  Mammal  from 
milk,  that  they  may  be  transformed  into  any  of  the  proteine-compounds 
which  are  to-be  found  in  the  Animal  body.  There  is  good  ground  to 
believe,  however,  that,  for  the  formation  of  all  the  Animal  tissues,  the 
presence  of  fatty  matter,  as  well  as  of  an  albuminous  compound  is  es- 
sential ;  and  it  is  a  circumstance  worthy  of  note,  that  in  both  the  fore- 
going cases,  fatty  matter  is  mingled  with  the  albumen,  in  the  aliment 
destined  for  the  development  of  the  young  animal.  This  subject,  how- 
ever, will  be  more  fully  discussed  hereafter. 

174.  The  Animal  derives  the  materials  of  its  nutrition,  however,  not 
only  from  the  Albuminous  compounds  furnished  by  flesh,  eggs,  and  milk, 
but  also  from  those  which  are  supplied  by  the  Vegetable  kingdom.  Every 
growing  Plant,  as  already  mentioned  (§12),  forms  albuminous  compounds 
by  the  combination  of  inorganic  elements,  as  the  pabulum  of  its  own 
tissues  ;  but  many  Plants  generate  them  in  much  larger  proportion,  and 
store  them  up  in  their  cells;  and  it  is  from  such,  that  Animals  derive 
their  largest  supply  of  nutritive  material.  Thus  the  gluten  of  wheat,  or 
the  tenacious  mass  which  is  left  after  the  removal  of  the  starch  by  wash- 
ing, is  principally  composed  of  a  substance  which  is  closely  allied  in 
composition  and  properties  to  the  Albumen  of  animals ;  being  moderately 
soluble  by  water,  coagulated  by  heat,  and  precipitated  by  acids  (except 
the  phosphoric  and  acetic)  and  by  metallic  salts ;  and  this  is  designated 
Vegetable  Albumen.  From  the  seeds  of  Leguminous  plants  a  substance 
termed  Legumin  may  be  separated,  which  corresponds  with  Caseine  in 
not  being  precipitated  by  heat,  and  also  in  the  absence  of  phosphorus ; 
hence  it  is  sometimes  designated  as  Vegetable  Caseine,  Various  other 
modifications  of  the  albuminous  principle  are  found  in  Plants ;  but  the 
foregoing  are  the  most  important  in  their  relations  to  the  nutrition  of 
Animals.  Like  flesh,  cheese,  &c.,  they  are  reduced  by  the  digestive 
process  to  the  state  of  soluble  Albumen;  and  in  this  form  they  are  taken 
up,  and  carried  into  the  circulation. 

175.  Next  in  importance  to  the  Albuminous  compounds  as  a  consti- 
tuent of  the  Animal  fabric,  is  Gelatine;  which  is  obtained  by  the  action 
of  boiling  water  on  White  Fibrous  tissue^  and  on  the  various  membranes, 
&c.,  of  which  this  is  the  chief  component.  The  composition  of  Gelatine 
is  much  simpler  than  that  of  the  Proteine-compounds,  so  far,  at  least, 
as  regards  the  number  of  atoms  of  its  several  elements ;  for  it  consists 
of  13  Carbon,  10  Hydrogen,  5  Oxygen,  2  Nitrogen.  This  composition 
is  the  same,  whether  the  Gelatine  be  obtained  from  isinglass,  from  fibrous 
membranes,  or  from  bones.  The  distinctive  characters  of  Gelatine  are 
its  solubility  in  warm  water,  its  coagulation  on  cooling  into  a  uniform 
jelly,  and  its  formation  of  a  peculiar  insoluble  compound  with  Tannic 
acid.     Gelatine  is  very  sparingly  soluble  in  cold  water ;  though  pro- 

:  longed  contact  with  it  will  cause  the  Gelatine  to  swell  up  and  soften. 


Ik 


112  CHEMICAL   COMPOSITION   OP  ANIMAL  TISSUES. 

Its  power  of  forming  a  jelly  on  cooling  is  such,  that  a  solution  of  one 
part  in  100  of  water  will  become  a  consistent  solid.     And  its  reaction 
with  Tannic  acid  is  so  distinct,  that  the  presence  of  one  part  of  Gelatine 
in  5000  of  water  is  at  once  detected  by  infusion  of  Galls.     There  can 
be  no  doubt  that  Gelatine  does  not  exist  exactly  as  such  in  the  Fibrous 
tissues ;  since  none  can  be  dissolved  out  of  them  by  the  continued  action 
of  cold  water,  and  it  usually  requires  the  prolonged  action  of  hot  water, 
to  occasion  their  complete  conversion.     There  afre  some  substances,  how- 
ever, in  which  this  is  not  requisite ;  and  from  which  the  -gelatine  may 
be  extracted  within  a  shorter  time.     This  is  the  case,  for  example,  w^ith 
the  air-bladder  of  the  Cod  and  other  fish;  which  when  cut  into  shreds 
and  dried,  is  known  as  Isinglass.     It  is  the  case  also  with  the  substance 
of  bones,  from  which  the  calcareous  matter  has  been  removed.     In  both 
instances  it  would  seem  that  the  state  of  organization  is  very  imperfect ; 
the  fibrous  structure  being  by  no  means  well-marked.     When  the  fibrous 
arrangement  is  more  complete,  the  solubility  of  the  tissue  is  much  di- 
minished.    Hence  it  would  seem  that  the  particles  have  a  difi*erent  ar- 
rangement in  the  tissues,  from  that  which  they  have  in  the  product 
obtained  by  boiling.     Their  ultimate  composition,  however,  is  the  same; 
for  when  any  serous  membrane,  or  other  tissue  principally  composed  of 
the  white  fibrous  element,  is  analysed  by  combustion,  the  elements  are 
found  to  have  the  same  proportion  to  each  other  as  in  Gelatine,  allow- 
ance being  made  for  the  small  admixture  of  other  substances.     The 
action  of  Tannic  acid,  too,  is  the  same  on  the  organized  tissue,  as  it  is 
on  the  gelatine  extracted  from  it ;  and  hence  results  its  utility  in  pro- 
ducing an  insoluble  compound,  not  liable  to  undergo  decomposition,  in 
the  substance  of  the  Skin,  converting  it  into  leather. 
.    176.  It  is  not  yet  known  how  Gelatine  is  produced  in  the  Animal  body. 
There  can  be  no  doubt  that  it  may  be  elaborated  from  Albumen  ;  since 
we  find  a  very  large  amount  of  Gelatine  in  the  tissues  of  young  animals, 
which  are  entirely  formed  from  albuminous  matter  ;  and  also  in  the 
tissues  of  herbivorous  animals,  which  cannot  receive  it  in  their  food,  as 
Plants  yield  no  substance  resembling  gelatine.     Carnivorous  animals, 
however,  will  receive  it  ready  formed,  as  part  of  their  aliment.     There 
is  no  reason  to  believe  that  it  is  capable  of  being  converted  into  Albu- 
men ;  and  consequently  it  can  never  be  applied  to  the  nutrition  of  the 
albuminous  tissues.    If  Gelatine  be  boiled  for  some  time  in  caustic  potash, 
it  is  decomposed,  with  an  escape  of  ammonia  ;  and  two  new  compounds, 
leucine,  and  glycoeoll  or  gelatine-sugar,  are  generated.     The  production 
of  leucine  from  Gelatine,  by  the  action  of  the  same  reagent  as  that 
which  caused  its  generation  from  Albumen,  is  a  fact  of  much  importance ; 
as  showing  that,  notwithstanding  their  difference  of  composition  and 
characters,  a  certain  similarity  in  the  arrangement  of  their  ultimfvte 
elements  still  subsists  between  these  two  bodies.     Glycoeoll  is  an  organic 
base  of  great  interest  from  its  relations  to  other  substances  ;  as  will  be 
shown  hereafter.     It  has  a  strong  sweet  taste,  and  is  very  soluble  in 
water,  from  which  it  may  be  crystallized  like  ordinary  sugar.     Its  compo- 
sition is  comparatively  simple ;  being  4  Carbon,  4  Hydrogen,  1  Nitrogen, 
3  Oxygen. 

177.  A  peculiar  modification  of  Gelatine,  which  presents  itself  in 


ALBUMINOUS  COMPOUNDS.  113 

Cartilage,  is  distinguished  as  Cfhondrine.  This  requires  longer  boiling 
than  gelatine  for  its  solution  in  water ;  but  the  solution  fixes  into  a  jelly 
in  cooling,  and  dries  by  evaporation  into  a  glue  that  cannot  be  distinguished 
from  that  of  gelatine.  Like  gelatine,  it  is  thrown  down  from  its  solution  by 
alcohol,  creasote,  tannic  acid,  and  bichloride  of  mercury ;  but  it  is  also 
precipitated  by  acetic  acid,  alum,  acetate  of  lead,  and  protosulphate  of 
iron,  which  do  not  disturb  a  solution  of  gelatine. — It  is  curious  that,  in 
proportion  as  Cartilages  become  fibrous,  their  Chondrine  gives  place  to 
Gelatine ;  and  during  the  progress  of  ossification,  the  Chondrine  seem& 
to  be  entirely  replaced  by  Gelatine,  of  which  the  fibrous  basis  of  the* 
bony  tissue  is  composed. 

178.  The  foregoing  may  be  considered  as  the  chief  among  the  "  raw 
materials"  of  the  Animal  fabric;  and  it  is  now  to  be  shown,  that  while 
the  Gelatinous  components  merely  become  subservient  to  the  formation 
of  tissues,  whose  structure  is  the  simplest  possible,  and  whose  function 
is  purely  mechanical^  the  destination  of  the  Albuminous  compounds  is 
much  higher ;  it  being  at  the  expense  of  the  latter  that  those  tissues  are 
generated,  which  are  the  instruments  of  the  purely  vital  operations  of 
the  Animal  economy.  In  their  progress  towards  the  state  of  complete 
organization,  however,  we  find  that  they  pass  through  an  intermediate 
condition,  which  is  one  that  requires  special  consideration.  The  fluids  that 
are  formed  at  the  expense  of  the  Albuminous  matters  which  have  been 
digested, and  absorbed,  contain  a  substance,  which  is  so  closely  related 
to  Albumen  in  its  ultimate  Chemical  composition,  as  not  to  be  distin- 
guishable from  it  with  any  degree  of  certainty,*  but  which,  though  still 
fluid  whilst  circulating  in  the  living  vessels,  exhibits  a  decided  tendency 
to  assume  the  organized  form,  and  manifests  properties  which  are  so 
diff"erent  from  those  of  inorganic  matter,  that  they  must  be  regarded  as 
vital.  This  substance  is  Fihrine.  It  is  found  in  the  Chyle,  or  crude 
blood,  soon  after  this  is  taken  up  from  the  food ;  it  presents  itself  in 
gradually  increasing  proportion,  as  the  Chyle  slowly  passes  along  the 
Lacteal  vessels,  and  through  the  Mesenteric  glands,  towards  the  termi- 
nation of  the  Absorbent  system  in  the  Venous ;  and  it  is  also  found  in 
the  fluid  contents  of  that  other  division  of  the  Absorbent  system,  the 
Lymphatics,  which  is  distributed  through  the  body  at  large,  and  which 
seems  to  have  for  its  chief  office  to  take  up,  and  to  reintroduce  into  the 
circulating  current,  such  particles  contained  in  the  fluids  of  the  tissues, 
as  do  not  require  to  be  at  once  cast  out  of  the  body,  but  may  be  again 
employed  in  the  process  of  Nutrition.  But  it  is  found,  above  all,  in  the 
Blood ;  the  fluid  whose  ceaseless  and  rapid  course  through  the  body  sup- 
plies to  every  element  of  the  structure  the  materials  of  its  growth  and 

*  According  to  some  analyses,  Fibrine  differs  slightly  from  Albumen  in  ultimate  com- 
position, the  proportions  x)f  its  several  constituents  in  1000  parts  being  as  follows  ; — 
Carbon  54G,  Hydrogen  70,  Oxygen  220,  Nitrogen  157,  Sulphur  4,  and  Phosphorus  3. 
The  difference  in  their  vital  relations,  hovrever,  is  far  greater  than  any  such  difference 
in  their  chemical  composition  can  account  for,  and  can  only  be  justly  attributed  to  the 
forces  brought  to  act  upon  the  fibrine  during  its  circulation  in  the  vessels  of  the  living 
body.  It  has  been  recently  maintained,  that  Fibrine  is  not  to  be  regarded  (as  here 
represented)  as  Albumen  in  the  transition-stage  of  incipient  organization,  but  that  it  is 
a  product  of  the  disintegration  of  the  tissues,  only  received  back  into  the  blood  in  order 
that  it  may  be  carried  out  of  the  system  through  the  excretory  channels.  For  a  discus- 
sion of  this  hypothesis,  see  the  Brit,  and  For.  Med.  Chir.  Review,  vol.  vii.  pp.  153,  473. 

8 


114  CHEMICAL   COMPOSITION   OF  ANIMAL   TISSUES. 

development :  and  the  varying  proportions  in  which  it  presents  itself 
there,  are  evidently  closely  connected  with  the  formative  powers  of  that 
fluid.  It  is  also  a  principal  element  of  certain  colourless  exudations^ 
which  are  put  forth  from  wounded  or  inflamed  surfaces,  or  which  are 
deposited  in  the  interstices  of  inflamed  tissues  ;  these  exudations,  when 
possessed  of  a  high  formative  property  (that  is,  a  readiness  to  produce 
an  organized  tissue),  are  said  to  be  composed  of  coagulahle  or  organi- 
zahle  lymph,  which  is  nothing  more  than  the  fibrinous  element  of  the 
blood,  in  an  unusually  concentrated  state.  We  shall  first  notice  the 
Chemical  properties  of  Fibrine  ;  and  shall  then  inquire  into  those,  which 
present  the  first  dawnings  or  indications  of  Vitality. 

179.  Like  the  other  Proteine-compounds,  Fibrine  may  exist  in 
solution,  or  in  an  insoluble  form ;  but  there  is  this  important  dif- 
ference,— that  its  soluble  form  is  not  a  permanent  one,  and  can- 
not be  maintained  in  any  fibrinous  fluid  that  has  been  drawn  from  the 
living  vessels,  without  the  influence  of  reagents,  which  totally  destroy 
its  peculiar  properties.  All  investigations  of  a  Chemical  nature,  there- 
fore, must  be  made  upon  insoluble  Fibrine ;  and  this  may  be  obtained  in 
its  purest  state,  by  whipping  fresh  blood  with  a  bundle  of  twigs,  by 
which  operation  it  will  be  caused,  in  coagulating,  to  adhere  to  the  twigs 
in  the  form  of  long,  white,  elastic  filaments,  with  scarcely  an  admixture 
of  foreign  matter.  Wh-en  dried  in  vacuo,  or  at  a  gentle  heat,  it  becomes 
translucent  and  horny ;  and  in  this  condition,  it  closely  resembles  coagu- 
lated albumen.  It  further  resembles  that  substance,  in  being  soluble  in 
very  dilute  caustic  alkali^  and  in  phosphoric  acid ;  and  the  solutions 
exhibit  many  of  the  properties  of  the  similar  solutions  of  albumen. 
"When  the  Fibrine  of  venous  blood  is  triturated  in  a  mortar  with  a  solu- 
tion of  nitrate  of,  potash,  and  the  mixture  is  left  for  twenty-four  hours 
or  more,  at  a  temperature  of  from  100°  to  120°,  it  becomes  gelatinous, 
slimy,  and  eventually  entirely  liquid.  In  this  condition,  it  exhibits  all 
the  properties  of  a  solution  of  Albumen  which  has  been  neutralized  by 
acetic  acid.  It  coagulates  by  heat ;  it  is  precipitated  by  alcohol,  corro- 
sive sublimate,  &c.;  and,  when  largely  diluted,  it  deposits  a  flocculent 
substance,  not  to  be  distinguished  from  insoluble  albumen.  The  close 
Chemical  relation  of  Fibrine  and  Albumen  is  further  proved  by  the  ready 
conversion  of  the  former  into  the  latter  in  the  act  of  digestion ;  Animal 
flesh,  which  consists  of  Fibrine,  being  reduced  to  the  form  of  Albumen 
with  the  same  facility,  as  the  Vegetable  compounds  which  resemble  the 
latter  much  more  closely  in  the  first  instance.  The  Fibrine  of  arterial 
blood,  however,  cannot  be  reduced  to  the  fluid  form  by  solution  with 
nitre  ;  and  this  appears  to  be  due  to  its  oxidized  condition  ;  for  in  a  solu- 
tion of  Venous  fibrine  in  nitre,  contained  in  a  deep  cylindrical  jar,  and 
having  its  surface  freely  exposed  to  the  air,  a  fine  flocculent  precipitate 
is  gradually  seen  to  form ;  and  this,  when  collected,  is  found  to  have  the 
properties  of  arterial  fibrine.  The  Fibrine  of  Animal  flesh  agrees  with 
that  of  venous,  rather  than  with  that  of  arterial  blood.  Fibrine,  like 
Albumen,  unites  with  acids  as  a  base,  forming  definite  compounds ;  and 
with  bases  as  an  acid.  It  also  possesses  the  property  of  uniting  with 
the  earthy  phosphates ;  of  which  from  0*7  to  2*5  per  cent,  are  found  in 
the  ash  that  is  left  after  its  combustion. 


FIBRINE. 


115 


1  : 


80.  We  see,  tlien,  that  when  considered  in  its  simply-Chemical  rela- 
tions, Fibrine  does  not  differ  in  any  essential  particular  from  i\.lbumen ; 
and  that  the  chief  point  of  obvious  variation,  is  the  spontaneous  coagu- 
lation of  the  former,  when  it  is  removed  from  the  living  body.  There 
is,  however,  in  the  structure  of  the  coagulum  itself,  a  most  important 
difference;  for  instead  of  consisting  of  a  homogeneous  structureless 
mass,  or  of  a  simple  aggregation  of  minute  granules,  it  is  found  by  the 
Microscope  to  possess  a  definite  fibrous  arrangement,  the  fibres  crossing 
one  another  in  every  direction.  In  the  ordinary  coagulum  or  clot  of 
Blood,  these  fibres  do  not  present  any  great  degree  of  firmness :  they 
may  be  hardened,  however,  by  boiling ;  and  their  arrangement  then 
becomes  more  definite.  They  may  be  seen  much  more  clearly,  however, 
in  the  "buffy  coat"  of  Inflammatory  blood ;  in  which  there  is  not  only 
an  increased  proportion  of  Fibrine,  but  the  Fibrine  itself  seems  to  have 
undergone  a  higher  elaboration,  that  is,  to  have  proceeded  still  further 
in  the  change  towards  regular  organization.  In  this  state,  the  process 
of  coagulation  is  unusually  slow ;  the  clot  formed  by  the  fibrous  tissue 
is  much  more  solid ;  and  it  continues  for  some  hours,  or  even  days,  to 
increase  in  solidity,  by  the  mutual  attraction  of  the  particles  composing 
the  fibres,  which  causes  them,  to  contract  and  to  expel  the  fluid  contained 
in  their  interstices. 

181.  The  most  perfect  fibrous  structure  originating  in  the  simple 
coagulation  of  fibrine,  is  to  be  found,  however,  in  those  exudations, 
which  take  place  either  from  inflammation,  or  from  a  peculiar  forma- 
tive action,  destined  to  repair  an  old  tissue  or  to  produce  a  new  one. 

Fig.  3. 


Fig.  2. 

) 

1 

Fibrous  structure  of  inflammatory  exudation 
from  peritoneum. 


Fibrous  membrane,  lining  the  egg-shell, 
and  forming  the  animal  basis  of  the  shell 
itself. 


'  Thus  in  Fig.  2  is  shown  the  fibrous  structure  of  a  false  membrane, 
i  formed  by  the  consolidation  of  a  fibrinous  exudation  from  the  surface  of 
I  an  inflamed  peritoneum.  And  in  Fig.  3  is  displayed  a  similar  fibrous 
i  structure  (in  which,  however,  the  fibres  have  more  of  a  reticulated  ar- 
trangement),  which  incloses  the  fluid  contents  of  the  egg,  and  enters 
'into  the  composition  of  the  shell  itself.  As  the  ovum  (which,  at  the 
;time  of  its  quitting  the  ovarium,  consists  of  the  yolk-bag  only)  passes 

along  the  oviduct  of  the  parent,  it  receives  its  coating  of  albuminous 
'matter,  of  which  layer  after  layer  is  thrown  out  by  the  vessels  of  the 

oviduct.     When  a  sufficient  supply  has  thus  been  furnished,  it  appears 


116  CHEMICAL   COMPOSITION   OF   ANIMAL  TISSUES. 

that  fibrinous  instead  of  albuminous  matter  is  poured  forth ;  and  this, 
in  coagulating,  forms  a  very  thin  layer  of  fibrous  tissue,  which  enve- 
lopes the  albumen.,  Layer  after  layer  is  gradually  added ;  and  at  last, 
by  the  superposition  of  these  layers,  that  firm  tenacious  membrane  is 
formed,  which  is  afterwards  found  lining  the  egg-shell.  The  process  is 
then  continued,  with  this  variation,  that  carbonate  of  lime  is  also  se- 
creted from  the  blood  in  a  chalky  state,  and  its  particles  lie  in  the  in- 
terstices of  the  fibrous  network,  and  give  it  that  solidity  which  is 
characteristic  of  the  shell.  If  they  be  removed  by  the  agency  of  a 
w^eak  acid,  or  if  the  bird  be  not  sufficiently  supplied  with  lime  at  the 
time  of  laying,  the  outer  membrane  has  the  same  consistence  as  the 
inner:  and  either  may  be  separated,  after  prolonged  maceration,  by 
dexterous  manipulation,  into  a  series  of  layers  of  a  fibrous  matting^  like 
that  represented  in  Fig.  3. 

182.  It  is  scarcely  possible  to  deny  to  such  a  tissue  the  designation 
of  an  organized  structure,  even  though  it  contains  no  vessels,  and  may 
not  participate  in  any  further  Vital  phenomena.  We  shall  hereafter 
find,  that  a  tissue  presenting  very  similar  characters  forms  a  large  part 
of  the  Animal  fabric ;  and  that  the  vessels  with  which  it  is  copiously 
supplied,  have  for  their  object  nothing  else  than  the  removal  of  its  dis- 
integrated or  decaying  portions,  and  the  deposition  of  new  matter  in  a 
similar  form  (§194).  In  the  production  of  new  parts,  we  find  this 
simple  fibrous  tissue  performing  the  important  function  of  serving  as  a 
matrix  or  bed  for  the  support  of  the  vessels ;  and  as,  by  the  more  gra- 
dual transformation  of  the  nutritive  materials  they  bring,  new  and  more 
permanent  tissues  are  formed,  the  original  one  gradually  undergoes  dis- 
integration, and  all  traces  of  it  are  in  time  lost.  This  would  appear  to 
be  the  history  of  the  Chorion  of  the  Mammalian  ovum ;  which  is  at 
first  nothing  else  than  a  fibrous  unvascular  bag,  formed  round  the  ovum 
in  its  passage  through  the  Fallopian  tube,  precisely  after  the  manner  of 
the  shell-membrane  of  the  Bird's  egg;  but  which  is  afterwards  pene- 
trated by  vessels  proceeding  from  the  embryo,  and  in  time  acquires  a 
new  structure  (chap,  xi.) 

183.  The  completeness  of  the  production  of  such  a  fibrous  tissue 
depends  in  part,  as  we  have  seen,  upon  the  degree  of  elaboration 
which  the  Fibrine  has  undergone ;  but  in  great  part  also  upon  the  na- 
ture of  the  surface,  on  which  the  coagulation  takes  place.  Thus  we 
never  find  so  perfect  a  membrane  formed  by  the  consolidation  of  the 
Fibrine  out  of  the  living  body, — on  a  slip  of  glass  for  example, — as 
when  it  takes  place  on  the  surface  of  a  living  membrane,  or  in  the  in- 
terstices of  a  living  tissue.  This  may  perhaps  be  accounted  for  by  the 
fact,  that  the  coagulation  takes  place  much  more  slowly  in  the  latter 
case  than  in  the  former,  and  that  the  particles  tnay  thus  have  more 
time  to  arrange  themselves  in  the  definite  fibrillation,  which  seems  to 
be  their  characteristic  mode  of  aggregation:  just  as  crystallization 
takes  place  best  when  the  action  is  slow ;  and  as  a  substance,  whose 
particles  would  remain  in  an  amorphous  or  disunited  form  if  too  rapidly 
precipitated  from  a  solution,  may  present  a  most  regular  arrangement 
when  they  are  separated  from  it  more  slowly.  Of  this  view  it  would 
seem  to  be  a  confirmation,  that  the  most  perfect  fibrillation  out  of  the 


^R( 


COAGULATION   OF  FIBRINE.  117 


dy  is  usually  seen'  in  those  cases,  in  which  coagulation  takes  place 
least  rapidly. 

184.  The  conditions  under  which  the  spontaneous  coagulation  of 
Fibrine  takes  place,  are  best  known  from  the  observation  of  that  pro- 
cess as  it  occurs  in  the  Blood ;  and  although  this  fluid,  as  we  shall  here-;- 
after  see,  is  of  a  very  complex  nature,  yet  as  the  Fibrine  alone  is  con- 
cerned in  its  coagulation,  and  as  that  act  appears  to  take  place  in  the 
same  manner  as  if  no  other  substance  was  present,  there  appears  to  be 
no  objection  to  the  employment  of  the  phenomena  of  Blood-coagulation 
as  the  basis  of  our  account  of  the  properties  of  Fibrine. — There  can  be 
no  doubt,  from  Microscopical  observation  of  the  circulating  Blood,  that 
Fibrine  is  in  a  state  of  perfect  solution  in  the  fluid ;  and  in  this  condi- 
tion it  remains,  so  long  as  it  is  in  motion  in  the  living  body.  That  its 
fluidity,  however,  does  not  depend  only  upon  its  movement,  is  evident 
from  two  facts ; — first,  that  no  kind  of  motion  seems  efi'ectual  in  pre- 
venting the  coagulation  of  the  blood,  after  it  has  been  drawn  from  the 
vessels ; — and  second,  that  a  state  of  rest  within  the  living  body  does 
not  immediately  produce  coagulation ;  a  portion  of  blood,  included  be- 
tween two  ligatures  in  a  living  vessel,  remaining  fluid  for  a  long  time ; 
and  blood  that  has  been  reduced  to  a  state  of  complete  stagnation  by 
inflammatory  action,  being  often  found  in  a  fluid  state  after  some  days. 
On  the  other  hand,  it  seems  certain  that  the  state  of  vitality  of  the 
parts  with  which  the  blood  is  in  contact,  has  a  great  influence  in  pre- 
serving its  fluidity ;  thus  it  has  been  found  that,  if  the  brain  and  spinal 
cord  of  an  animal  be  broken  down,  and  by  this  measure  the  vitality  of 
the  body  at  large  be  lowered,  clots  of  blood  are  formed  in  their  trunks 
within  a  few  minutes.  Nevertheless,  a  mass  of  blood  eff'used  into  a 
cavity  of  the  living  body,  undergoes  coagulation  almost  as .  soon  as  it 
would  in  a  dead  vessel ;  but  this  may  be  accounted  for  by  the  very  small 
surface  which  is  in  contact  with  the  blood,  as  compared  with  the  mass 
of  the  latter.  It  must  be  remembered  that  the  circulating  blood  is  con- 
tinually being  subdivided  into  countless  streams ;  and  that  each  of  these 
passes  through  the  living  tissue,  in  such  a  manner  that  all  its  particles 
are  in  close  relation  with  the  living  surface.  Moreover  it  is  probable 
that  the  form  of  matter  which  we  term  Fibrine,  never  remains  long  in 
that  condition,  in  the  ordinary  state  of  the  system ;  being  continually 
withdrawn  by  the  nutritive  processes,  and  as  continually  re-formed  from 
the  Albumen,  by  an  elaborating  action  hereafter  to  be  considered. 
Hence  we  may  regard  the  state  of  motion  through  living  vessels,  as 
essential  to  the  permanent  continuance  of  fibrine  in  the  fluid  form. 

185.  The  length  of  time,  however,  during  which  Fibrine  may  remain 
uncoagulated,  after  it  has  been  withdrawn  from  the  living  body,  varies 
according  to  various  conditions  ;  some  of  which  are  not  well  understood. 
In  the  first  place,  as  already  remarked,  the  more  elaborated  and  more 
concentrated  the  condition  of  the  Fibrine,  the  more  slowly  does  it 
usually  coagulate.  Thus  when  a  large  quantity  of  blood  is  drawn,  at 
one  bleeding,  into  several  vessels,  that  which  flows  first  takes  the  longest 
time  to  coagulate,  and  forms  the  firmest  clot :  whilst  that  which  is  last 
drawn  coagulates  most  rapidly,  and  with  the  least  tenacity.  The  coagu- 
lation is  accelerated  by  moderate  heat,  and  retarded  by  cold ;  but  it  is 


k 


118  CHEMICAL   COMPOSITION   OF   ANIMAL   TISSUES. 

not  prevented  even  by  extreme  cold ;  for  if  blood  be  frozen  immediately 
that  it  is  drawn,  it  will  coagulate  on  being  thawed, — thus  preserving  its 
vitality,  in  spite  of  the  freezing  process,  like  the  organized  structures  of 
many  of  the  lower  animals.  Again,  the  coagulation  is  accelerated  by 
exposure  to  air ;  but  it  is  not  prevented,  though  it  is  retarded,  by  com- 
plete exclusion  from  it.  Various  Chemical  agents  retard  the  coagula- 
tion, without  preventing  it ;  this  is  the  case  especially  with  solutions  of 
the  neutral  salts.  The  coagulation  is  not  so  firm,  however,  or  the 
fibrillation  so  perfect,  after  the  use  of  these ;  and  there  can  be  no  doubt 
that  they  modify  the  properties  of  the  fibrine,  by  acting  chemically 
upon  it. 

186.  After  remaining  in  this  condition  for  a  certain  length  of  time, 
the  Fibrine  undergoes  a  further  change,  which  is  evidently  the  result  of 
decomposition ;  the  coagulum  becomes  soft,  and  exhibits  appearances  of 
putrefaction.  This  takes  place  the  more  rapidly,  as  the  first  coagula- 
tion was  less  complete.  Thus  in  the  imperfectly-elaborated  Fibrine  of 
the  Chyle,  the  coagulum  is  sometimes  so  incomplete,  that  it  does  not 
separate  itself  from  the  serum,  and  liquefies  again  in  half  an  hour.  In 
certain  states  of  disease,  the  solidifying  properties  of  the  Fibrine  are 
very  much  impaired ;  so  that  it  soon  liquefies  and  decomposes.  In  these 
cases,  there  is  scarcely  any  trace  of  the  characteristic  fibrous  arrange- 
ment of  the  particles.  On  the  other  hand,  the  fibrinous  coagulum  of 
inflamed  blood,  as  it  is  more  solid,  is  also  more  persistent  than  that  of 
ordinary  blood  ;  and  the  greatest  persistency  of  all  is  seen  in  the  fibrous 
network  formed  by  exudation,  as  in  the  cases  just  now  mentioned. 

187.  The  coagulating  power  of  Fibrine, — in  other  words,  its  peculiar 
vital  property, — may  be  destroyed  by  various  causes  operating  within 
the  living. body;  so  that  the  blood  remains  fluid ^after  death.  These 
may  be  classed  under  three  heads.  In  the  first  place,  the  vitality  of 
the  fibrine  may  be  destroyed  by  substances  introduced  into  the  blood 
from  without ;  which  have  the  power  of  acting  in  the  manner  of  ferments, 
and  which  occasion  an  obvious  chemical  change  in  its  condition.  Such 
is  the  case  in  those  severe  forms  of  Fever  which  are  termed  malignant; 
and  especially  those  which  result  from  the  contact  of  putrescent  matter, 
as  Glanders,  Pustule  maligne,  &c.  Secondly,  it  may  be  impaired  or 
altogether  destroyed  by  morbid  actions  originating  in  the  system  itself, 
and  depending  upon  irregular  nutrition  or  imperfect  excretion ;  thus  the 
blood  has  been  found  fluid  after  death  in  severe  cases  of  Scurvy  and 
Purpura,  also  in  cases  of  Asphyxia  (consequent  upon  the  retention  of 
carbonic  acid  in  the  blood),  and  in  the  bodies  of  overdriven  animals. 
The  same  result  may  follow,  Thirdly,  from  violent  shocks  or  impressions, 
which  suddenly  destroy  the  vitality  of  the  whole  system  at  once ;  these 
may  be  such  as  are  obviously  capable  of  producing  a  chemical  or  me- 
chanical change,  as  in  the  case  of  death  by  Lightning  or  by  a  violent 
Electrical  discharge ;  or  they  may  act  through  the  nervous  system,  in 
a  manner  not  yet  clearly  understood,  as  when  death  results  from  con- 
cussion of  the  brain,  from  a  blow  upon  the  epigastrium,  from  violent 
mental  emotion,  or  from  a  coup  de  soleil. — It  is  not  to  be  supposed  that 
the  non-coagulability  of  the  Blood  is  a  phenomenon  by  any  means  inva- 
riable under  the  foregoing  circumstances;  but  it  has  been  occasionally 


SIMPLE   FIBROUS   TISSUES. 


119 


2.    Of  the  Simple  Fibrous  Tissues. 


observed  in  all  of  them.  We  must  not  mistake  for  the  absence  of  coagu- 
lating potver,  the  remarkable  retardation  of  the  act  of  coagulation  which 
;  sometimes  occurs.  Thus,  the  blood  is  occasionally  found  in  a  fluid  con- 
dition in  the  bodies  of  persons  that  have  been  dead  for  some  days ;  and 
yet  when  withdrawn  from  the  vessels,  it  coagulates. 

I 

■^f  188.  A  large  part  of  the  Animal  fabric,  especially  among  the  higher 
r  classes  in  which  the  parts  have  the  greatest  amount  of  motion  upon  one 
another,  is  composed  of  tissues,  which  seem  as  if  they  consisted  of 
nothing  else  than  fibres,  of  the  simple  character  already  described, 
woven  together  in  various  ways,  according  to  the  purposes  they  are 
I  destined  to  serve.  These  fibres  are  altogether  different  from  those 
•  hereafter  to  be  described  as  constituting  the  Muscular  and  Nervous  tis- 
sues, and  must  not  be  confounded  with  them.  The  former  are  solid, 
and  possess  none  but  physical  properties  ;  the  latter  are  tubular,  and 
are  distinguished  by  their  peculiar  vital  endowments,  which  seem  chiefly, 
if  not  entirely,  to  reside  in  the  contents  of  the  tubular  fibre.  The  Sim- 
ple Fibrous  tissues,  of  which  we  have  now  to  treat,  appear  to  have  it  for 
their  sole  office  in  the  animal  body  to  bind  together  the  other  elementary 
parts  into  one  whole,  without  uniting  them  so  closely  as  to  render  them 
immovable ;  and  we  find  the  same  elements  arranged  in  very  different 
modes,  according  to  the  purposes  they  are  destined  to  fulfil.  Thus  in 
the  Tendons,  by  which  the  muscles  are  connected  with  the  bones,  and 
impart  motion  to  them,  the  only  property  required  is  that  of  resisting 
strain  or  tension  in  one  direction ;  and  in  these  we  find  the  fibres  dis- 
posed in  a  parallel  arrangement,  passing  continuously  in  straight  line 
between  the  points  of  attachment.  In  the  Ligaments  which  connect 
the  bones  together,  and  which  also  have  for  their  purpose  to  afford 
resistance  to  strain,  but  which  are  liable  to  tension  in  a  greater  variety 
of  directions,  we  find  bundles  of  fibres  crossing  each  other  according  to 
these  directions ;  and  in  some  instances  we  find  the  ligaments  endowed 
also  with  a  certain  degree  of  elasticity.     The  structure  of  the  strong 

Fig.  4. 


Simple  fibrous  tissue;  a,  fibres  of  areolar  tissue;  6,  tendinous  fibres. 

Fibrous  Membranes,  which  form  the  envelopes  to  different,  organs  and 
bind  together  the  contained  parts,  is  very  similar ;  each  of  these  mem- 
branes being  composed  of  several  layers  of  a  dense  network,  formed  by 


I 


120 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 


the  interweaving  of  bundles  of  fibres  in  different  directions.  In  the 
FihrO'CartilageSj  we  find  a  mixture  of  the  characteristic  structure  of 
Ligament  with  that  of  Cartilage ;  bundles  of  fibres,  similar  to  those 
which  constitute  the  former,  being  disposed  among  the  cells  which  are 
the  chief  organized  constituents  of  the  latter.  In  certain  Eibro-Carti- 
lages,  however,  these  fibres  are  endowed  with  a  high  degree  of  elasticity. 

189.  These  two  qualities, — that  of  resistance  to  tension  without  any 
yielding — and  that  of  resistance  combined  with  elasticity, — are  charac- 
teristic of  two  distinct  forms  of  Fibrous  tissue,  the  ^Vhite  and  the  Yellow. 
The  White  Fibrous  tissue  presents  itself  under  various  forms,  being  some- 
times composed  of  fibres  so  minute  as  to  be  scarcely  distinguishable ; 
and  sometimes  presenting  itself  under  the  aspect  of  bands,  usually  of  a 
flattened  form,  and  attaining  the  breadth  of  l-500th  of  an  inch.  These 
bands  are  marked  by  numerous  longitudinal  streaks,  but  they  cannot  be 
torn  up  into  minute  fibres  of  determinate  size ;  hence  they  must  be  re- 
garded as  made  up  of  an  aggregation  of  the  same  elements  as  those 
which  liiay  become  developed  into  separate  fibres.  The  fibres  and  bands 
are  occasionally  somewhat  wavy  in  their  direction.  The  tissue,  which  is 
perfectly  inelastic,  is  easily  distinguished  from  the  other  by  the  effect  of 
Acetic  acid,  which  swells  it  up,  and  renders  it  transparent,  at  the  same 
time .  bringing  into  view  certain  oval  corpuscles,  which  are  supposed  to 
be  the  nuclei  of  the  cells  that  were  concerned  in  the  formation  of  the 
tissue. 

190.  The  Yellow  Fibrous  tissue  exists  in  the  form  of  long,  single, 
elastic,  branched  filaments,  with  a  dark  decided  border,  which  are  dis- 
posed to  curl  when  not  put  on  the  stretch.  They  are  for  the  most  part 
between  l-5000th  and  l-10,000th  of  an  inch  in  diameter ;  but  they  are 
often  met  with  both  larger  and  smaller.  They  frequently  anastomose, 
so  as  to  form  a  network,  as  shown  in  Fig.  6.     This  tissue  does  not  un- 


Fig.  6. 


Fig.  6. 


Fasciculus  of  fibres  of  white  fibrous  tissue; 
from  lateral  ligament  of  knee  joint. 


Yellow  fibrous  tissue  from  ligamentum 
nuchns;  a,  the  fibres  drawn  apart,  to  show 
their  reticulate  arrangement;  6,  the  fibres 
in  situ. 


dergo  any  change,  when  treated  with  acetic  acid.  It  exists  alone  (that 
is,  without  any  mixture  of  the  white)  in  parts  which  require  a  peculiar 
elasticity,  such  as  the  middle  coat  of  the  Arteries,  the  Chordae  Vocales, 
the  Ligamentum  Nuchas  (of  Quadrupeds)  and  the  Ligamenta  subflava ; 
it  enters  largely  into  the  composition  of  certain  parts,  which  are  com- 


SIMPLE   FIBHOUS   TISSUES. 


121 


monly  regarded  as  Cartilaginous,  such  as  the  external  ear;  and  it  is  also 
a  principal  component  of  other  tissues  to  be  presently  described. 

191.  These  tissues  are  very  different  in  Chemical  composition.  Those 
which  are  composed  of  the  White  fibrous  element, — namely,  Tendons, 
Ligaments,  &c. — are  almost  entirely  resolved  by  long  boiling  into  G-ela- 
tine;  and  this  substance  is  also  largely  obtained  from  the  Skin,  and 
from  Mucous  and  Serous  membranes,  of  which,  as  we  shall  presently 
see,  that  element  is  a  principal  component ;  whilst  it  is  also  yielded  in 
great  quantity  by  Bones,  whose  animal  basis  is  almost  entirely  gelatinous. 

192.  The  composition  of  the  Yellow  fibrous  tissue  appears  to  be  alto- 
gether dissimilar.  It  scarcely  undergoes  any  change  by  prolonged  boil- 
ing ;  it  is  unaffected  also  by  the  weaker  acids ;  and  it  preserves  its 
elasticity,  if  kept  moist,  for  an  almost  unlimited  period.     According  to 

:  Scherer,  it  consists  of  48  Carbon,  38  Hydrogen,  6  Nitrogen,  and  16 
Oxygen ;  and  he  considers  it  to  be  composed  of  an  atom  of  Proteine 
with  two  atoms  of  water.  (See  §  171.) 

193.  The  simple  Fibrous  tissues  appear  to  be 
1  very  little  susceptible  of  change  in  the  living  body ; 

and  we  find  them  very  sparingly  supplied  with 
blood-vessels.     In  the  solid  Tendons,  the  bundles 
of  straight  parallel  fibres  are  a  little  separated 
from  each  other  by  the  intervention  of  the  Areolar 
tissue  to  be  presently  noticed ;.  and  this  permits 
the  sparing  access  of  vessels  to  their  interior.     In 
■  the   Fibrous  Membranes  and  Ligaments,  this  is 
!  found  in  somewhat  larger  amount ;  and  the  vascu- 
larity of  these  tissues  is  rather  greater.     Two  dif- 
:  ferent  views  of  their  mode  of  development  have 
I  been  taken  by  those  who  have  studied  it.    By  some 
it  has  been  maintained  that  the  White  fibres  are 
first  developed  as  cells,  which  progressively  be- 
come elongated  and  solidified ;  their  nuclei  at  the 
j  same  time  disappearing,  until  brought  into  view 
by  acetic  acid  (Fig.  7) ;  and  the  Yellow  fibres  have 
j  been  supposed  to  have  a  similar  origin.     By  others 
I  it  has  been  considered  that  the  White  fibres  are  produced  by  the  direct 
i  fibrillation  of  a  blastema  or  plastic  exudation  (§  181),  and  that  the  Yellow 
I  proceed  from  the  nuclear  particles  which  this  contains;  no  development 
j  of  cells  being  requisite  for  the  production  of  either.     The  recent  inqui- 
ries of  Mr.  Paget  and  others  tends  to  show  that  both  these  methods  are 
I  adopted  in  the  production  of  the  fibrous  tissue  which  is  developed  for 
'  the  repair  of  injuries  in  the  adult  body ;  the  former  being  seen  in  the 
.  reparation  of  external  wounds  to  which  air  has  access ;  the  latter  in  the 
'organization  of  "coagulable  lymph"  effused  into  internal  cavities,  or 
into  the  interstices  of  tissue,  altogether  secluded  from  it. 

194."  The  great  use  of  the  foregoing  tissues  appears  to  be,  to  afford  a 
!  firm  resistance  to  tension ;  by  which  they  may  either  communicate  motion, 
j  a$  in  the  case  of  Tendons ;  or  restrain  it,  as  in  thfe  case  of  Ligaments ; 
i  or  altogether  prevent  it,  as  in  the  case  of  Aponeuroses  and  Fibrous 
i  Membranes.     With  this  firm  resistance,  a  considerable  amount  of  elas- 


Development  of  fibres  from 
cells: — a,  circular  or  oval  nu- 
cleated cells;  6,  the  same  be- 
coming pointed;  c,  the  same 
become  fusiform,  the  nuclei 
being  still  apparent;  d,  the 
same  elongating  into  fibres, 
the  nuclei  having  disappeared. 


122  STRUCTURE   AND    ENDOWMENTS    OF   ANIMAL   TISSUES. 

ticity  may  be  combined.  But  we  have  now  to  notice  a  tissue,  in  which 
a  v«ry  different  arrangement  of  the  same  elements  presents  itself;  and 
the  object  of  this  is,  to  bind  together  the  elements  of  the  different  fabrics 
of  the  body,  and  at  the  same  time  to  endow  them  with  a  greater  or  less 
degree  of  freedom  of  movement  upon  one  another.  The  tissue,  which 
is  called  the  Areolar,  consists  of  a  network  of  minute  fibres  and  bands, 
which  are  interwoven  in  every  direction,  so  as  to  leave  innumerable 
areolce  or  little  spaces,  which  communicate  freely  with  one  another.  Of 
these  fibres,  some  are  of  the  yellow  or  elastic  kind ;  but  the  majority 
are  composed  of  the  white  fibrous  tissue,  and,  as  in  that  form  of  ele- 
mentary structure,  they  frequently  present  the  form  of  broad  flattened 
bands,  or  membranous  shreds,  in  which  no  distinct  fibrous  arrangement 
is  visible.  The  interstices  are  filled  during  life  with  a  fluid,  which 
resembles  very  dilute  serum  of  the  blood ;  consisting  chiefly  of  water, 
but  containing  a  sensible  quantity  of  common  salt  and  albumen.  This 
tissue  (which  has  been  frequently  but  erroneously  termed  Cellular)  is 
very  extensible  in  all  directions,  and  very  elastic,  from  the  structural 
arrangement  of  its  elements.  It  cannot  be  said  to  possess  an}^  dis- 
tinctly vital  endowments ;  for  although  it  has  a  certain  amount  of  sensi- 
bility, this  merely  depends  upon  the  presence  of  nerves  which  it  is  con- 
veying to  other  parts ;  and  the  small  amount  of  contractility  which  it 
shows,  depends  rather  upon  the  muscular  tissue  of  the  vessels  that  tra- 
verse it. 

195.  As  already  mentioned,  we  find  this  tissue  in  almost  every  part 
of  the  body ;  thus  it  binds  together  the  ultimate  fibres  of  the  Muscles 
into  minute  fasciculi,  unites  these  fasciculi  into  larger  ones,  these  again 
into  larger  ones  which  are  obvious  to  the  eye,  and  these  into  the  entire 
muscle.  Again  it  forms  the  membranous  septa  between  distinct  mus- 
cles, or  between  muscles  and  fibrous  aponeuroses.  In  like  manner  it 
unites  the  elements  of  nerves,  glands,  &c. ;  binds  together  the  fat-cells 
into  minute  bags,  these  into  larger  ones,  and  so  on  ;  and  in  this  manner 
•penetrates  and  forms  a  considerable  part  of  all  the  softer  tissues  of  the 
body.  But  it  is  a  great  mistake  to  assert,  as  it  was  formerly  common 
to  do,  that  it  penetrates  the  harder  organs,  such  as  bones,  teeth,  carti- 
lage, &c.  Its  purpose  obviously  is,  to  allow  a  certain  degree  of  move- 
ment of  the  parts  which  it  unites ;  and  hence  we  find  it  entering  much 
more  largely  into  the  composition  of  the  Mammary  gland  (w^hich,  from 
its  attachment  to  the  great  pectoral  muscle,  must  have  its  parts  capable 
of  being  shifted  upon  one  another),  than  into  that  of  the  Liver,  Kid- 
neys, &c.  It  also  serves  as  the  bed,  in  which  blood-vessels,  nerves,  and 
lymphatics  may  be  carried  into  the  substance  of  the  different  organs ; 
and  it  often  undergoes  a  degree  of  condensation,  in  order  to  form  a 
sheath  for  the  larger  trunks,  which  gives  it .  almost  the  characters  of  a 
Fibrous  Membrane. 

196.  The  quantity  of  fluid  in  the  interstices  of  Areolar  tissue  is  sub- 
ject to  considerable  variations;  but  these  depend  rather  upon  the  state 
of  fulness  or  emptiness  of  the  vessels  which  traverse  it,  and  upon  the 
condition  of  the  walls  of  those  vessels,  than  upon  any  change  in  the 
tissue  itself.  It  has  been  shown  that,  when  an  albuminous  fluid  is  in 
contact  with  an  animal  membrane,  the  watery  part  of  the  fluid  will  pass 


AREOLAR   TISSUE. 


123 


through  by  transudation ;  but  that  the  albuminous  matter  will  be  for 
the  most  part  kept  back,  so  that  only  a  very  small  proportion  of  it  is  to 
be  found  in  the  transuded  liquid.     This  appears  to  be  a  sufficient  ex- 
planation of  the  presence  of  a  weak  serous  fluid  in  the  cavities  of  areolar 
tissue  ;  and  there  is  not  any  necessity,  therefore,  to  imagine  the  exist- 
ence of  a  secreting  power,  either  in  the  areolar  tissue  itself,  or  in  the 
walls  of  the  capillaries  which  traverse  it.     When  there  is  a  want  of 
firmness  or  tone  in  the  walls  of  the  vessels,  producing  (as  we  shall  here- 
after see,  §  609)  an  increased  pressure  of  the  contained  fluid  on  their 
walls,  and  diminished  resistance,  the  watery  part  of  the  blood  will  have 
an  unusual  tendency  to  transudation :  and  we  accordingly  find  that  it 
then  distends  the  areolae,  and  produces  dropsy.     The  physical  arrange- 
ment of  the  parts  of  the  tissue  is  so  much  altered,  that  its  elasticity  is 
impaired  ;  and  it  consequently  p)its  on  pressure, — that  is,  when  pressure 
has  made  an  indentation  in  the  surface,  this  is  not  immediately  filled  up 
when  the  pressure  is  withdrawn,  but  a  pit  remains  for  some  seconds  or 
ven  minutes.     The  free  communication  which  exists  among  the  inter- 
tices,  is  shown  by  the  influence  of  gravity  upon  the  seat  of  the  dropsi- 
al  efi'usion ;  this  always  having  the  greatest  tendency  to  manifest  itself 
the  most  depending  parts, — a  result,  however,  which  is  also  due  to 
he  increased  delay  that  takes  place  in  the  circulation  in  such  parts, 
hen  the  vessels  are  deficient  in  tone.     This  freedom  of  communication 
fcis  still  more  shown,  however,  by  the  fact,  that  either  air  or  water  may 
e  made  to  pass  by  a  moderate  continued  pressure,  into  almost  every 
art  of  the  body  containing  Areolar  tissue  ;  although  introduced  at  only 
single  point.     In  this  manner  it  is  the  habit  of  butchers  to  inflate 
veal :  and  impostors  have  thus  blown  up  the  scalps  and  faces  of  their 
children,  in  order  to  excite  commiseration.     The  whole  body  has  been 
thus  distended  with  air  by  emphysema  in   the  lung;   the  air  having 
escaped  from  the  air-cells  into  the  surrounding  areolar  tissue,  and  thence, 
by  continuity  of  this  tissue  with  that  of  the  body  in 
general  at  the  root   or   apex  of  the  lungs,  into  the 
entire  fabric. 

197.  The  structure  of  the  Sey^oiis  and  Synovial 
Membranes  is  essentially  the  same  with  that  of  Areolar 
tissue.  It  is  the  peculiar  character  of  these  mem- 
branes to  form  closed  bags  or  sacs,  having  a  very 
Smooth  and  glistening  inner  surface,  and  containing 
a  fluid  more  or  less  allied  in  composition  to  the 
serum  of  the  blood.  The  disposition  of  the  Syno- 
vial membranes  may  be  understood  by  studying  one 
of  the  simpler  forms  of  the  joints,  such  as  is  repre- 
sented in  the  accompanying  diagram;  but  although 
originally  continuous  over  the  surfaces  of  the  Articu- 
lar Cartilages,  the  Synovial  membrane  does  not  con- 
tinue to  be  distinctly  traceable  after  the  joint  has  come 
into  play,  and  its  vessels  retreat  from  the  portion  over  brams  covering  the  arti 

\  •    -t       •,  o  ^  culated     surfaces,     and 

wiucn  the  two  surfaces  are  exposed  to  friction,  but  passing  from  one  to  the 

form  a  circle  round  its  margin,  from  which  the  Carti-  ''*^^''' 

lage  is  nourished  (§  278).~The  arrangement  of  the  Serous  membranes 


Fig.  8. 


Ideal  seijtion  of  a  Joint ; 
— a,  a,  the  extremities  of 
the  two  articulated  bones; 

b,  b,  the  layers  of  carti- 
lage which  cover  them; 

c,  c,  c,  c,  synovial  mem- 


124  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

is  usually  much  more  complicated.  These  line  the  three  great  cavities 
of  the  body, — the  head,  chest,  and  abdomen, — together  with  their  sub- 
divisions ;  enveloping  the  viscera  which  these  contain,  so  as  to  afford 
them  an  external  coating  over  every  part  save  that  by  which  they  are 
suspended ;  and  being  then  reflected  over  the  interior  of  the  cavity,  so  as 
to  form  a  shut  sac  intervening  between  its  outer  w^alls  and  its  contents. 
The  chief  purpose  of  this  appears  to  be,  to  facilitate  the  movements  of 
the  contained  organs,  by  forming  smooth  surfaces  which  shall  freely 
glide  over  each  other ;  this  is  evidently  of  great  importance,  where  such 
constantly  moving  organs  as  the  heart  and  lungs  are  concerned. 

198.  The  free  or  unattached  surface  of  these  membranes  is  covered 
with  a  layer  of  cells;  but  these  constitute  a  distinct  tissue,  the  Epithe- 
lium^ of  which  an  account  will  be  given  hereafter.  The  epithelium  lies 
upon  a  continuous  sheet  of  membrane,  of  extreme  delicacy,  in  which  no 
definite  structure  can  be  discovered ;  the  nature  of  this,  which  is  called 
the  basement  or  primary  membrane^  will  be  presently  considered  (§  206). 
Beneath  this  is  a  layer  of  condensed  Areolar  tissue,  which  constitutes 
the  chief  thickness  of  the  serous  membrane,  and  confers  upon  it  its 
strength  and  elasticity ;  this  gradually  passes  into  that  laxer  variety, 
by  which  the  membrane  is  attached  to  the  parts  it  lines,  and  which  is 
commonly  known  as  the  sub-serous  tissue.  The  yellow  fibrous  element 
enters  largely  into  the  composition  of  the  membrane  itself;  and  its  fila- 
ments interlace  in  a  beautiful  network,  which  confers  upon  it  equal  elas- 
ticity in  every  direction.  The  membrane  is  traversed  by  blood-vessels, 
nerves,  and  lymphatics,  in  varying  proportions ;  some  of  the  synovial 
membranes,  especially  that  of  the  knee-joint,  are  furnished  with  little 
fringe-like  projections,  which  are  extremely  vascular,  and  which  seem 
especially  concerned  in  the  secretion  of  the  synovial  fluid.  The  fluid  of 
the  serous  cavities  is  so  nearly  the  same  as  the  serum  of  the  blood,  that 
the  simple  act  of  transudation  is  sufficient  to  account  for  its  presence  in 
their  sacs  ;  on  the  other  hand,  that  of  the  Synovial  capsules,  and  of  the 
Bursas  Mucosae  which  resemble  them,  may  be  considered  as  serum  with 
from  6  to  8  per  cent,  of  additional  albumen. 

199.  The  elements  of  Areolar  tissue  enter  largely  also  into  two  other 
textures,  which  perform  a  most  important  share  in  both  the  Organic  and 
the  Animal  functions  ; — ^namely,  the  Mucous  Membranes  and  the  Skin. 
These  textures  are  continuous  with  each  other  ;  and  may,  in  fact,  be  con- 
sidered as  one  and  the  same,  modified  in  its  different  parts  according  to 
the  function  it  is  destined  to  perform.  Thus  it  is  everywhere  extremely 
vascular  ;  but  the  supply  of  blood  in  the  Skin  is  chiefly  destined  for  the 
nervous  system,  and  is  necessary  to  the  act  of  sensation ;  whilst  that  of 
the  internal  skin  or  Mucous  Membrane  is  rather  subservient  to  the  pro- 
cesses of  absorption  and  secretion.  This  tissue  is  continued  inwards 
from  the  external  surface  of  the  body,  by  the  several  orifices  and  outlets 
of  its  cavities ;  and  it  is  further  continued  most  extensively  from  its 
primary  internal  prolongations,  into  the  inmost  recesses  of  the  glandular 
structures. 

200.  Thus  the  G-astro-intestinal  mucous  membrane  commences  at  the 
mouth,  and  lines  the  whole  alimentary  canal  from  the  mouth  to  the  anus, 
where  it  again  becomes  continuous  with  the  skin ;  and  it  sends  off  as 


^^&rar 


SKIN,   AND   MUCOUS   MEMBRANES.  *  125 


ranches,  the  membranous  linings  of  the  ducts  of  the  salivary  glands, 
pancreas,  and  liver ;  these  membranes  proceed  into  all  the  subdivisions 
of  the  ducts,  and  line  the  ultimate  follicles  or  caeca  in  which  they  ter- 
minate. Again,  the  Bronchio-pulmonary  mucous  membrane  commences 
at  the  nose,  and  passes  along  the  air-passages,  down  the  trachea,  through- 
the  bronchi  and  their  subdivisions,  to  line  the  ultimate  air-cells  of  the 
lungs ;  communicating  in  its  course  with  the  gastro-intestinal.  Another 
mucous  membrane  of  small  extent  commences  at  the  puncta  lachrymalia, 
lines  the  lachrymal  sac  and  the  nasal  duct,  and  becomes  continuous  with 
the  preceding.  Another,  which  may  be  considered  a  kind  of  offset  from 
either  of  the  first  two,  passes  up  from  the  pharynx  along  the  Eustachian 
tube,  and  lines  the  cavity  of  the  tympanum. 

201.  Near  the  opposite  termination  of  the  alimentary  canal,  more- 
over, we  have  the  Gienito-urinary  mucous  membranes  ;  these  commence 
in  the  male  by  a  single  external  orifice,  that  of  the  urethra ; — passing 
backwards  along  the  urethra,  the  genital  division  is  given  off,  to  line  the 
seminal  ducts,  the  vesiculae  seminales,  the  vasa  deferentia,  and  the  secre- 
ting tubuli  of  the  testis ;  another  division  proceeds  along  the  ducts  of 
the  prostate  gland,  to  line  its  ultimate  follicles,  and  another  along  the 

I  ducts  of  Cowper's  glands ;  whilst  the  urinary  division  lines  the  bladder, 
passes  up  along  the  ureters  to  the  kidney,  and  then  becomes  continuous 
with  the  membrane  of  the  tubuli  uriniferi.  In  the  female,  the  urinary 
division  commences  at  once  from  the  vulva ;  whilst  the  genital  passes 
along  the  vagina  into  the  uterus,  and  thence  along  the  Fallopian  tubes 
to  their  fimbriated  extremities,  where  it  becomes  continuous  with  the 
serous  lining  of  the  abdominal  cavity,  the  peritoneum. 

202.  Besides  the  glandular  prolongations  here  enumerated,  there  are 
many  others,  both  from  the  internal  and  external  surface.  Thus  we 
have  the  Mammary  mucous  membrane,  commencing  from  the  orifices  of 
the  lactiferous  ducts,  passing  inwards  to  line  their  subdivisions,  and 
forming  the  walls  of  the  ultimate  follicles.  In  the  same  manner  the 
Lachrymal  mucous  membrane  is  prolonged  from  the  conjunctival  mucous 
membrane,  which  covers  the  eye  and  lines  the  eyelids,  and  which  is  con- 
tinuous with  the  skin  at  their  edges.  There  are  several  minute  glands, 
again,  in  the  substance  of  the  skin,  and  in  the  walls  of  the  alimentary 
canal,  which  need  not  be  here  enumerated;  but  which  contribute 
immensely  to  the  extension  of  the  surface  of  the  mucous  membrane,  a 
prolongation  of  this  being  the  essential  constituent  in  every  one.  In 
their  simplest  form,  these  glandulae  are  nothing  more  than  little  pits 
or  depressions  of  the  surface ;  these  are  found  both  in  the  Skin  and 
Mucous  membrane,  and  are  particularly  destined  for  the  prouduction  of 
their  protective  secretions,  hereafter  to  be  described. 

203.  We  have  seen,  then,  that  the  essential  character  of  the  Mucous 
membranes,  as  regards  their  arrangement,  is  altogether  different  from 
that  of  the  serous  and  synovial  membranes.  For  whilst  the  latter  form 
shut  sacs,  the  contents  of  which  are  destined  to  undergo  little  change, 
the  former  constitute  the  walls  of  tubes  or  cavities,  in  which  constant 
change  is  taking  place,  and  which  have  free  outward  communications. 
Thus  in  the  gastro-intestinal  mucous  membrane,  we  have  an  inlet  for  the 
reception  of  the  food,  and  a  cavity  for  its  solution,  the  walls  of  which 


126  STRUCTURE   AND    ENDOWMENTS    OF   ANIMAL   TISSUES. 

are  endowed  in  a  remarkable  degree  with  absorbing  power,  whilst  they 
are  also  furnished  with  numerous  glandulse,  which  pour  the  solvent  fluid 
into  the  cavity.  On  the  other  hand,  it  has  an  outlet,  through  which  the 
indigestible  residuum  is  cast  forth,  together  with  the  excretions  from  the 
various  glands  that  pour  their  products  into  the  alimentary  tube.  In  the 
bronchio-pulmonary  apparatus,  the  same  outlet  serves  for  the  introduc- 
tion and  for  the  expulsion  of  the  air  ;  and  here,  too,  is  continual  change. 
In  other  cases,  there  is  but  a  single  outlet ;  and  the  change  is  of  a  simpler 
character,  consisting  merely  in  the  expulsion  of  the  matters  eliminated 
from  the  blood  by  the  agency  of  the  glands.  Now  it  is,  as  we  shall  see 
hereafter,  im  the  digestion  and  absorption  of  food,  on  the  one  hand,  and 
in  the  rejection  of  effete  matters  on  the  other,  that  the  commencement 
and  termination  of  the  nutrient  processes  consist ;  and  these  operations 
are  performed  by  the  system  of  Mucous  membranes,  including  in  that 
general  term  the  Skin,  which  is  an  important  organ  of  excretion,  besides* 
serving  as  the  medium  through  which  sensory  impressions  of  a  general 
character  are  received  by  the  Nervous  system. 

204.  The  Mucous  Membrane  may  be  said,  like  the  Serous,  to  consist 
of  three  chief  parts  ; — the  epithelium  or  epidermis  covering  its  free  sur- 
face ; — the  subjacent  basement-membrane  ; — and  the  areolar  tissue,  with 
its  vessels,  nerves,  &c.,  which  forms  the  thickness  of  the  membrane,  and 
connects  it  with  the  subjacent  parts.  The  Epidermis  and  Epithelium 
alike  consist  of  cells ;  but  the  function  of  the  former  (which  consists  of 
several  layers,  of  which  the  outer  are  dry  and  horny)  is  simply  protec- 
tion to  the  delicate  organs  beneath ;  whilst  that  of  the  latter  is  essen- 
tially connected  with  the  process  of  Secretion,  as  will  be  shown  hereafter. 
The  basement-membrane  resembles  that  of  the  serous  membranes ;  but 
its  separate  existence  is  unusually  evident  in  some  parts  where  it  exists 
alone,  as  in  the  tubuli  uriniferi  of  the  kidney ;  whilst  it  can  with  diffi- 
culty be  demonstrated  in  others,  as  the  skin.  The  Areolar  tissue  of 
Mucous  membranes  usually  makes  up  the  greatest  part  of  their  thick- 
ness ;  and  it  is  so  distinct  from  that  of  the  layers  beneath,  constituting 
the  sub-mucous  tissue,  as  to  be  readily  separable  from  them.  It  differs 
not  in  any  important  particular,  however,  from  the  same  tissue  else- 
w^here ;  and  the  white  and  fibrous  elements  may  be  detected  in  it  in 
varying  proportions,  in  different  parts, — the  latter  being  especially 
abundant  in  the  skin  and  lungs,  which  owe  to  it  their  peculiar  elas- 
ticity. Hence  the  Mucous  membranes  yield  Gelatine  in  abundance,  on 
being  boiled.  The  skin  also  appears  to  contain  some  of  the  non-striated 
Muscular  fibre  {§  337),  in  varying  proportions  in  its  different  parts. 

205.  The  relative  amount  of  Blood-vessels,  Nerves,  and  Lymphatics, 
as  already  mentioned,  is  subject  to  great  variation,  according  to  the 
part  of  the  system  examined.  The  first,  however,  are  most  constantly 
abundant,  being  required  in  the  Skin  for  sensation  (Fig.  9),  and  in  the 
Mucous  membranes  for  absorption  and  secretion  (Figs.  10,  11,  12).  In 
fact  we  might  say  of  many  of  the  mucous  membranes,  especially  those 
of  the  glands,  that  their  whole  purpose  is  to  give  support  to  the  secreting 
cells,  and  to  convey  blood-vessels  into  their  immediate  neighbourhood, 
whence  these  cells  may  obtain  materials  for  their  development.  The 
Skin  is  the  only  part  of  the  whole  system  which  is  largely  supplied  with 


BASEMENT    OR    PRIMARY   MEMBRANE. 


127 


Nerves  (Fig.  13),  except  the  Conjunctival  membrane  and  the  Mucous 
membrane  of  the  mouth  and  nose ;  hence  the  sensibility  of  the  internal 


Fig.  9. 


Fig.  10. 


Distribution  of  Capillaries  at  the  surface 
of  the  skin  of  the  finger. 


Distribution  of  Capillaries  in  the  Villi  of 
the  Intestine. 


mucous  membrane  is  usually  low,  although  its  importance  in  the  organic 
functions  is  so  great.    The  Skin  is  copiously  supplied  with  Lymphatics ; 


Fig.     11; 


Fig.  12. 


Distribution  of  Capillaries  around  follicles 
of  Mucous  Membrane. 


Distribution  of  Capillaries  around  the  follicles 
of  Parotid  Gland. 


and  the  first  part  of  the  alimentary  canal  with  Lacteals ;  some  of  the 
glandular  organs   are   also   largely  supplied  with   Lymphatics. — The 

Fig.  13. 


Distribution  of  the  tactile  nerves  at  the  extremity  of  the  human  thumb,  as 
seen  in  a  thin  perpendicular  section  of  the  skin. 

Areolar  tissue,  whether  existing  separately,  or  forming  a  part  of  the 
Serous  and  Mucous  Membranes,  is  capable  of  being  vgry  quickly  and 
completely  regenerated ;  indeed,  we  often  find  that  losses  of  substance 
in  other  tissues  are  replaced  by  means  of  it. 

■^K  3.    Of  the  Basement  or  Primary  'Membrane. 

f  ^206.  In  many  parts  of  the  Animal  body,  we  meet  with  membranous 
:    expansions  of  extreme  delicacy  and  transparency,  in  which  no  definite 


128  STRUCTURE   AND    ENDOWMENTS    OF   ANIMAL   TISSUES. 

Structure  can  be  discovered ;  and  these  seem,  like  the  simple  fibres 
already  described,  to  have  been  formed,  rather  directly  from  the  nutri- 
tive fluid,  than  indirectly  by  any  previous  process  of  transformation. 
Hence  we  may  regard  such  membranes  and  fibres,  as  constituting  the 
most  simple  or  elementary  forms  of  Animal  tissue.  The  characters  of 
membranes  of  this  kind  were  first  pointed  out  by  Mr.  Bowman  and 
Prof.  Goodsir ;  by  the  former  of  whom  it  was  termed  baseinent-mem- 
brane,  as  being  the  foundation  or  resting-place  for  the  epithelium-cells 
which  cover  its  free  surface  (§  231) ;  whilst  by  the  latter  it  was  termed 
the  primary  membrane,  as  furnishing  the  germs  of  those  cells.  These 
terms  appear  equally  appropriate,  and  may  be  used  indifferently. — In 
its  very  simplest  form,  the  basement-membrane  is  a  pellicle  of  such 
extreme  delicacy,  that  its  thickness  scarcely  admits  of  being  measured ; 
it  is  to  all  appearance  perfectly  homogeneous,  and  presents  not  the 
slightest  trace  of  structure  under  the  highest  powers  of  the  microscope, 
appearing  like  a  thin  film  of  coagulated  gelatine.  Examples  of  this 
kind  may  be  easily  procured,  by  acting  upon  the  inner  layer  of  any 
bivalve  shell  with  dilute  acid ;  this  dissolves  away  the  calcareous  matter, 
and  leaves  the  basement-membrane.  In  other  cases, 
however,  the  membrane  is  not  so  homogeneous ;  a 
number  of  minute  granules  being  scattered,  with 
more  or  less  of  uniformity,  through  the  transparent 
substance.  And  we  not  unfrequently  find,  in  place 
of  these  uniformly  distributed  granules,  a  series  of 
distinct  spots,  arranged  at  equal  or  variable  distances, 
and  in  different  directions,  as  shown  in  Figure  14. 
Moreover,  the  membrane  thus  constituted  is  disposed 
to  break  up  into  portions  of  equal  size,  each  of  which 
contains  one  of  these  spots  ;  whilst  in  the  more  homo- 
membraSeV tleh^^Z.  goncous  forms  prcviously  described,  we  find  no  such 
uZti^^tl  lirj^  tendency,  no  appearance  of  any  definite  arrangement 
spots,  or  nutritive  centres  j^eiuff  perceptible  whou  thcv  are  torn. — Hence  it  would 

diffused  over  it.  -c     ^        n  i      •         ^  n  ^  t 

seem  as  it  the  first  and  simplest  lorm  were  produced 
by  the  simple  consolidation  of  a  thin  layer  of  homogeneous  fluid ;  the 
second,  by  a  layer  of  such  fluid,  including  nuclear  granules ;  and  the 
third,  by  the  coalescence  of  flattened  cells,  whose  further  development 
had  been  checked,  but  whose  nuclei  continue  to  perform  their  peculiar  ' 
functions  (§  212).  We  find  the  primary  membrane,  under  one  or  other 
of  these  forms,  on  all  the  free  surfaces  of  the  body,  beneath  the  epithe- 
lial or  epidermic  cells.  Thus,  as  already  mentioned,  it  constitutes  the 
outer  layer  of  the  true  Skin ;  it  lines  all  the  cavities  formed  by  Mucous 
membranes,  and  is  prolonged  into  all  the  ducts  and  ultimate  follicles 
and  tubuli  of  the  Glands  which  are  connected  with  them  (§  199) :  indeed 
it  may  be  said  in  many  instances  to  be  the  sole  constituent  of  the  walls 
of  these  follicles  and  tubuli,  the  subjacent  tissue  not  being  continued  to 
their  finest  ramifications.  Again,  it  forms  the  innermost  layer  of  the 
Serous  and  Synovial  membranes  ;  and  it  also  lines  the  blood-vessels  and  ^ 
lymphatics,  forming  the  sole  constituent  of  the  walls  of  their  minutest  ■ 
divisions.  P 

207.  In  every  one  of  these  cases,  we  find  the  free  aspect  of  the  Pri- 


BASEMENT   OR   PRIMARY  MEMBRANE.  129 

mary  Membrane  in  contact  with  cells,  which  form  a  more  or  less  conti- 
nuous layer  upon  its  surface.  These  cells  can  only  receive  their  nutri- 
ment by  the  imbibition  of  fluid,  through  the  primary  membrane,  from 
the  blood  brought  to  its  attached  surface,  by  the  capilLary  vessels  of  the 
tissue  with  which  it  is  in  relation.  Thus  in  the  Skin  and  Mucous_ 
membranes,  a  very  copious  supply  of  blood  is  brought  to  the  attached 
surface  of  the  primary  membrane,  by  the  minutely-distributed  capilla- 
ries which  form  a  large  part  of  the  subjacent  tissue  ;  and  it  is  from  these 
that  the  epidermis  and  epithelium  draw  their  nourishment,  through  the 
primary  membrane.  In  like  manner,  the  ultimate  follicles  and  tubuli 
of  the  Glands  are  surrounded  by  a  copious  network  of  capillaries  (Fig. 
12) ;  and  it  is  from  these,  through  the  primary  membrane,  that  the  cells 
of  these  follicles  draw  their  nourishment.  Hence  this  membrane,  in 
every  instance,  forms  a  complete  septum,  on  the  one  hand  between  the 
stream  of  blood  in  the  vessels  and  the  surrounding  tissues,  since  it  forms 
the  lining  even  of  the  minutest  capillaries ;  and  on  the  other  between 
the  fluids  in  the  interstices  of  the  substance  of  the  true  skin,  the  mucous 
membranes,  &c.,  and  the  cells  covering  their  free  surfaces.  It  is  evi- 
dent, therefore,  that  whilst  bounding  these  tissues  and  restraining  the 
too-free  passage  of  fluids  from  their  surfaces,  it  allows  the  transudation 
of  a  sufficient  amount  for  the  nutrition  of  the  cells  which  lie  upon  it ; 
and,  as  we  shall  presently  see,  these  cells  frequently  pass  through  all 
their  stages  of  growth  so  rapidly,  that  a  very  free  supply  of  nutriment 
must  be  required  by  them.  Hence,  notwithstanding  its  apparent  homo- 
geneousness,  the  primary  membrane  must  have  a  structure  which  readily 
admits  the  passage  of  fluid.  In  this  respect  it  corresponds  with  the 
membrane,  which  forms  the  wall  of  the  cells  of  both  Animal  and  Vege- 
table tissues ;  for  this  also  appears  completely  homogeneous  and  struc- 
tureless, when  seen  under  its  simplest  aspect,  and  yet  allows  the  free 
passage  of  fluids  from  one  cell  to  another. 

208.  But  it  is  probable  that  this  membrane  performs  a  much  more 
important  office  than  that  of  simply  limiting  the  fluids,  whilst  allowing 
the  requisite  transudation.  We  can  scarcely  account  for  the  new  pro- 
duction of  cells,  which  (as  will  presently  appear)  is  continually  taking 
place  on  its  surface,  without  referring  to  it  as  the  originator  of  these 
cells, — that  is,  as  the  source  of  their  germs.  The  new  generations  of  cells 
cannot  here  be  developed  by  the  reproductive  powers  of  the  old  ones 
(§  212) ;  since  the  latter  are  often  completely  cast  ofi"  entire,  before  they 
liberate  the  reproductive  granules ;  or  they  undergo  changes  which 
evidently  unfit  them  for  such  a  purpose..  Thus  in  the  Epidermis  we 
shall  find  that  they  become  flattened  into  dry  scales,  forming  an  almost 
horny  layer  on  the  surface  of  the  body  ;  whilst  the  new  cells  are  origina- 
ting beneath,  from  the  surface  of  the  basement-membrane  (§  224  and  Fig. 
20).  Hence  we  cannot  find  any  other  origin  for  4:hese  cells,  than  in  the 
basement-membrane  itself;  and  there  seems  every  probability  that  the 
granules,  which  have  been  mentioned  as  being  frequently  diffused  through 
it,  are  in  reality  the  germs  of  cells  to  be  developed  frdm  its  surface ; 
whilst  the  distinct  spots  are  collections  of  similar  granules,  each  of  which 
may  give  origin  to  a  large  number  of  such  cells,  which  spring  from  them 
as  from  a  centre.     We  shall  presently  see  that  these  "  germinal  centres" 

9 


130  STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

closely  resemble  the  nuclei  of  cells  in  general,  from  which  it  is  unques- 
Fig.  15.  tionable  that  the  new  crops  of  cells  may  arise  (§  212). 

The  only  difference  is,  that  in  the  latter  case,  the 
groups  of  new  cells  are  for  a  time  contained  within  the 
parent-cell  (Fig.  18) ;  whilst  in  the  former  they  are 
developed  on  the  free  surface  of  the  basement-mem- 
brane. In  Eig.  15  is  shown  a  portion  of  the  same 
Component  cells  of  membrane  as  that  represented  in  Fig.  14  ;  but  havinsj 

primary    membrane,  t^  .^.  ,.,  O 

with  adherent  epithe-  bccn  rendered  transparent  by  acetic  acid,  its  real  nature 
as  a  layer  of  flattened  nucleated  cells  is  more  obvious ; 
the  nucleus  or  germinal  spot  of  the  central  cell  has  given  origin  to  a 
cluster  of  oval  epithelial  cells,  of  which  five  still  adhere  to  it. 

209.  Hence  we  are  probably  to  regard  this  primary  or  basement-mem- 
brane as  a  transitional^  rather  than  as  a  peTtnanejit  structure ;  and  to 
look  upon  it  as  furnishing  the  germs  of  all  the  cells,  which  are  developed 
upon  its  surface  ;  as  well  as  serving  for  the  medium,  through  which  they 
are  supplied  with  nutriment.  It  must  be  continually  undergoing  disin- 
tegration, therefore,  on  its  free  surface :  and  must  be  as  continually 
renewed,  at  the  side  in  relation  with  the  blood-vessels. 

4.    Of  Simple  Isolated  Cells,  employed  in  the  Organic  Functions. 

210.  'The  active  functions  of  the  Animal  body  are  performed,  to  a 
much  greater  extent  than  was  until  lately  believed,  by  the  agency  of 
simple  isolated  cells ;  of  which  every  one  grows  and  lives  quite  inde- 
pendently of  the  rest,  just  as  if  it  were  one  of  the  simplest  Cellular 
Plants  (§  30) ;  but  of  which  all  are  dependent  upon  the  general  nutritive 
fluid  for  the  materials  of  their  development,  imbibing  it  from  the  cur- 
rents that  circulate  in  their  neighbourhood.  It  may  be  said,  indeed, 
that  all  the  Vegetative  functions  of  the  body, — all  the  processes  of 
Nutrition  and  Reproduction, — all  those  operations,  in  short,  which 
are  common  to  Plants  and  Animals, — are  performed  in  the  Animal 
and  Vegetable  structures  by  the  very  same  means,  the  agency  of  cells ; 
and  this  is  true,  not  only  of  the  healthy  actions,  but  of  various  morbid 
operations,  in  which  the  unusual  development  of  cells,  possessing  peculiar 
endowments,  performs  a  most  conspicuous  part.  Hence  it  will  be  neces- 
sary to  enter  somewhat  at  large  into  the  history  of  cell-development  in 
the  Animal  body :  and  the  various  modifications  under  which  this  process 
may  take  place.  In  fact,  a  knowledge  of  the  Physiology  of  Cells  may 
be  regarded  as  the  foundation  of  all 'accurate  acquaintance  with  that 
department  of  the  Science,  which  relates  to  the  Nutritive  and  Repro- 
ductive processes  ;  and  it  has  a  considerable  bearing,  as  we  shall  see 
hereafter,  upon  the  history  of  the  purely  Animal  functions. 

211.  The  history  of  the  Animal  cell,  in  its  simplest  form,  is  essen- 
tially that  of  the  Vegetaljle  cell  of  the  lowest  kind :  excepting  in  so  far 
as  it  is  dependent  for  its  nutriment  upon  organic  compounds  previously 
elaborated,  instead  of  generating  these  for  itself.  It  lives  for  itself 
and  hy  itself ;  and  is  dependent  upon  nothing  but  a  due  supply  of  nutri- 
ment, and  of  the  appropriate  stimuli,  for  the  continuance  of  its  growth 
and  for  the  due  performance  of  all  its  functions,  until  its  term  of  life  be 
expired.     In  whatever  method  it  originates  (and  we  shall  presently  see 


SIMPLE   ISOLATED    CELLS. 


131 


that  the  life  of  an  independent  cell  may  commence  in  variotis  modes),  it 
attracts  to  itself,  assimilates,  and  organizes,  the  particles  of  the  nutrient 
fluid  in  its  neighbourhood  ;  converts  some  of  them  into  the  substance  of 
its  cell-wall,  whilst  it  draws  others  into  its  cavity ;  in  this  manner  the 
cell  gradually  increases  in  size  ;  and  whilst  it  is  itself  approaching  the 
term  of  its  life,  it  may  make  preparation  for  its  renewal,  by  the  deve- 
lopment of  reproductive  particles  in  its  interior,  which  may  become  the 
germs  of  new  cells,  when  set  free  from  the  cavity  of  the  parent.  In  the 
interior  of  most  Animal  cells,  usually  attached  to  some  part  of  their  wall, 
is  seen  a  collection  of  granular  matter,  which  is  called  the  nucleus  (Fig. 
16  a).  This  appears  to  be  the  centre  of  the  vital  forces  of  the  cell ; 
being  the  part  through  which  it  specially  exerts  its  agency  on  the  sub- 
stances brought  under  its  influence  ;  and  being  also  the  chief  instrument 
in  the  reproductive  operation.     There  is  reason  to  believe,  indeed,  that 

t  clear  bodies  may  exert  their  vital  power,  and  may  efi'ect  the  transfor- 


Fig.  16. 

"O^^ 

/u^l^ 

1      1     1       J 

Vf 

\^'^^:^:/\ 

Cells  from  chorda  dorsalis  of  Lamprey,  a,  a,  nuclei. 


mation  or  new  arrangement  of  organic  compounds,  without  the  forma- 
tion of  a  cell-membrane ;  the  purpose  of  the  latter,  indeed,  being  appa- 
rently to  bound  or  limit  the  substances  drawn  together  by  the  nucleus, 
and  to  cut  them  ofi"  from  others  in  their  neighbourhood.  When  the  for- 
mation of  a  cell  is  complete,  and  it  is  not  destined  to  reproduce  its  kind, 
the  nucleus  frequently  disappears  ;  this  is  the  case,  for  example,  with 
the  Red  corpuscles  of  the  Blood  of  Mammalia  (§  215),  and  also  with  Fat- 
cells  (§  257). — So  far  as  is  yet  known,  however,  the  composition  of  the 
cell-wall  is  everywhere  the  same  ;  being  that  of  Proteine.  It  is  in  the 
nature  of  the  contents  of  the  cell,  that  (as  among  the  cells  of  Plants)  the 
greatest  diversity  exists ;  and  we  shall  find  that  the  purposes  of  the  dif- 
ferent groups  of  cells,  in  the  Animal  economy,  depend  upon  the  nature 
of  the  products  they  secrete,  and  upon  the  mode  in^  which  these  products 
are  given  back,  after  they  have  been  subjected  to  the  action  of  the 
cells. 

212.  New  cells  may  originate  in  one  of  the  two  principal  modes  :•  either 
directly  from  a  pre-existing  cell ;  or  by  an  entirely  new  production  in 
the  midst  of  an  organizable  blastema.  The  development  of  new  cells 
from  a  pre-existing  cell,  again,  may  take  place  in  one  of  two  modes ; 
either  by  the  subdivision  of  the  parent-cell,  or  by  the  production  of  a 
number  of  new  cells  in  its  interior ;  the  nucleus^  in  each  case,  appearing 
to  perform  an  important  part  in  the  process.  Of  the  multiplication  of 
cells  by  subdivision,  we  have  a  characteristic  example  in  the  growth  of 
Cartilage,  which  repeats  in  adult  age  the  process  by  which  the  develop- 
ment of  the  "  germinal  mass"  takes  place  at  the  earliest  period  of  embry- 


132 


STRUCTURte   AND   ENDOWMENTS   OF   ANIMAL   TISSUES. 


onic  life  (chap,  xi.)  The  process  of  subdivision  seems  to  commence  in 
the  nucleus,  which  tends  to  separate  itself  into  two  equal  parts ;  and 
each  of  these  draws  around  it  a  portion  of  the  contents  of  the  cell,  so 
that  the  cell-wall,  which  is  at  first  merely  inflected  inwards  by  a  sort  of 
hour-glass  contraction,  at  last  forms  a  complete  partition  between  the 
two  halves  of  the  original  cavity  (Fig.  17,  a-d).  The  process  of  subdi- 
vision may  be  again  repeated,  either  in  the  same  or  in  a  contrary  direc- 
tion, 80  as  to  produce  four  cells,  either  linearly  arranged  (f,  g,  h),  or 
clustered  together  (e)  ;  and  this  duplication  may  take  place  until  a  large 
mass  has  been  produced  by  the  subdivision  of  a  single  original  cell. — In 

Fig.  17. 


Multiplication  of  Cartilage-cells  by  duplication:— a,  original  cell ;  b,  the  same  beginning  to  divide;  c,  the 
same  sho-wing  complete  division  of  the  nucleus ;  D,  the  same  with  the  halves  of  the  nucleus  separated,  and 
the  cavity  of  the  cell  subdivided ;  e,  continuation  of  the  same  process,  with  cleavage  in  contrary  direction,  to 
form  a  cluster  of  four  cells ;  F,  a,  h,  production  of  a  longitudinal  series  of  cells,  by  continuation  of  cleavage 
in  the  same  direction. 

other  cases,  however,  the  nucleus  appears  to  break  up  at  once  into  several 
fragments,  each  of  which  may  draw  around  it  a  portion  of  the  contents 
of  the  parent-cell,  which  becomes  invested  by  a  cell-wall  of  its  own  ;  and 
thus  the  cavity  of  the  parent-cell  may  at  once  become  filled  with  a  whole 
brood  of  young  cells,  without  any  successive  subdivision.  Of  this  pro- 
cess we  frequently  have  examples  in  the  case  of  morbid  growths,  in  which 
the  multiplication  of  cells  often  takes  place  with  great  rapidity  (Fig.  18). 

Fig.  18. 


Parent-cells,  a,  a,  of  cancerous  structure,  containini;  secondary  cells,  b,  b,  each  having  one, 
two,  or  three,  nuclei,  c,  c. 

Generally. speaking,  the  former  method  seems  to  prevail  in  structures 
which  have  a  comparatively  permanent  destination  ;  whilst  the  latter  is 
adopted  in  cases  in  which  the  life  of  the  cells  thus  generated  is  but  transi- 


t 


SIMPLE   ISOLATED    CELL^.  133 

tory,  or  in  which  they  are  not  destined  to  reproduce  themselves.  Thus 
the  follicles  of  Glands  (§  238)  are  but  parent-cells,  in  whose  wall  an 
opening  has  been  formed  for  the  liberation  of  the  cells  of  the  new  gene- 
ration (which  are  the  real  instruments  of  the  secreting  process)  as  fast 
as  they  are  formed;  and  from  the  nuclei  or  "germinal  spots"  of  these — 
parent-cells,  which  occupy  the  blind  extremity  of  the  follicles,  successive 
crops  of  young  cells  are  generated,  at  the  expense  of  the  fresh  materials 
which  the  nuclei  are  continually  drawing  from  the  blood.  So  the  nuclear 
particles  scattered  through  the  "basement-membranes"  (§  208),  probably 
give  origin  to  the  epithelial  cells  developed  upon  their  free  surfaces ; 
even  though  these  nuclei  have  never  been  themselves  included  within 
cells. 

213.  In  the  production  of  cells  de  novo  in  the  midst  of  an  organiza- 
ble  blaste7na,  or  plastic  exudation,  we  cannot  trace  with  the  same  dis- 
tinctness the  instrumentality  of  pre-existing  cells.  This  blastema,  when 
first  effused,  presents  the  appearance  of  a  homogeneous,  semi-fluid,  sub- 
stance ;  as  it  solidifies,  however,  it  becomes  dimly  shaded  by  minute 
dots  ;  and  as  it  is  acquiring  further  consistence,  some  of  these  dots  seem 
to  aggregate,  so  as  to  form  little  round  or  oval  clusters  bearing  a  strong 
resemblance  to  cell-nuclei.  These  bodies  appear*  to  be  the  centres  of 
the  further  changes  which  take  place  in  the  blastema ;  for  if  it  be  about 
to  undergo  a  development  into  a  fibrous  tissue,  they  seem  to  be  the  cen- 
tres from  which  the  fibrillation  takes  place ;  whilst  if  a  cellular  struc- 
ture is  to  be  generated,  it  is  from  them  that  the  cells  take  their  origin. 
The  first  stage  of  the  latter  process  appears  to  consist  in  the  accumula- 
tion round  each  nucleus  of  the  substance  which  the  cell  is  to  include ; 
and  around  this  the  cell-membrane  is  subsequently  developed.  Such  is 
the  mode,  then,  in  which  the  development  of  new  structures,  for  the 
filling-up  of  losses  of  substance,  is  provided  for ;  and  it  appears  from 
the  observations  of  Mr.  Paget,  that  whilst  the  immediate  fibrillation  of 
the  blastema  takes  place  in  the'  case  of  effusions  which  are  secluded 
from  the  air  and  which  undergo  organization  under  the  most  favourable 
circumstances,  a  production  of  cells  takes  place  when  the  blastema  is 
poured  out  upon  the  surface  of  an  open  wound,  where  the  contact  of 
air,  and  other  sources  of  irritation,  interfere  with  the  organizing  pro- 
cess, and  occasion  a  tendency  to  degradation  in  the  newly-generating 
tissue. — Such  a  production  of  cells  de  novo  in  the  midst  of  an  organiza- 
ble  blastema,  does  not  constitute,  however,  any  real  exception  to  the 
general  rule,  of  the  dependence  of  the  life  of  ever^  cell  upon  that  of  a 
pre-existing  cell.  For  it  is  pretty  certain  that  the  blastema  is  itself  the 
product  of  the  formative  agency  of  certain  cells  expressly  provided  for 
its  elaboration ;  and  it  does  not  seem  improbable  that  these  cells,  in 
bursting  and  setting  free  the  plastic  fluid  which  they  have  prepared, 
should  diffuse  through  it  their  own  nuclear  or  germinal  particles  in  a 
state  of  solution  or  extremely  minute  division ;  and  that  these,  attract- 
ing each  other  in  the  act  of  solidification,  should  act  as  new  centres  of 
cell-growth,  just  as  if  they  were  still  contained  within  the  parent-cell. 

214.  The  very  simplest  and  most  independent  condition  of  the  Ani- 
mal Cell  is  probably  to  be  found  in  the  Blood,  the  Chyle,  and  the 
Lymph ;  in  all  of  which  liquids  we  meet  with  floating  cells,  which  are 


134 


STRUCTURE  AND   ENDOWMENTS   OP   ANIMAL   TISSUES. 


completely  isolated  from  one  another,  and  which  are  consequently  just 
as  independent  as  the  vesicles  of  the  Red  Snow  or  other  simple  cellular 
Plants.  Indeed  in  the  nature  of  their  habitat^  we  may  compare  them 
with  the  Yeast-Plant ;  for  as  this  will  only  vegetate  in  a  saccharine  fluid 
containing  vegetable  albumen,  so  do  we  find  that  these  floating  cells 
will  only  grow  and  multiply  in  the  albuminous  fluids  of  animals.  In 
their  general  appearance  they  very  closely  correspond  with  the  figure 
already  given  as  the  type  of  the  simple  cell.  Their  diameter  is  pretty 
uniform  in  the  different  fluids  of  the  body,  and  even  in  diff'erent  animals ; 
being  for  the  most  part  about  l-3000th  of  an  inch.  They  are  some- 
times nearly  spherical,  and  sometimes  flattened;  when  they  present  the 
latter  shape,  they  may  be  made  to  swell  out  into  the  spherical  form 
(see  Frontispiece^  Figs.  4  and  5)  by  the  action  of  water,  which  they  im- 
bibe according  to  the  laws  of  Endosmose, — the  thinner  fluid,  watei:, 
passing  towards  the  more  viscid  contents  of  the  cell,  and  mingling  with 
them.  By  the  continuance  of  this  kind  of  action,  the  cell  will  be  caused 
to  burst.  These  cells,  which  are  known  as  the  corpuscles  of  the  Chyle 
and  Lymph,  and  as  the  White  Corpuscles  of  the  Blood,  are  observed  to 
contain  a  number  of  minute  molecules  in  their  interior  [Front.  Fig.  4) ; 

Fig.  19. 


Colourless  cells,  •with  active  molecules,  and  fibres  of  fibrine,  from  Herpes  labialis. 

and  at  a  certain  stage  of  their  development, — probably  that  which  im- 
mediately precedes  the  maturation  and  rupture  of  the  parent-cell, — 
these  molecules  may  be  seen,  with  a  good  Microscope,  in  active  move- 
ment within  the  cavity.  The  action  of  a  very  dilute  solution  of  potash 
causes  the  immediate  rupture  of  these  cells,  and  the  discharge  of  the 
contained  molecules,  which  are  probably  the  germs  of  new  cells  of  a 
similar  character.  And  when  they  rupture  spontaneously,  which  they 
are  much  disposed  to  do  under  the  influence  of  contact  with  air,  the 
fluid  which  they  set  free  shows  an  obvious  tendency  to  assume  a  fibrous 
arrangement. — The  cells  which  are  found  in  many  fibrinous  exudations 
resemble  the  colourless  corpuscles  of  the  blood  in  all  essential  particu- 
lars (Fig.  19).  Hence  it  may  be  concluded  that  they  belong  to  the 
same  class ;  being  probably  developed  from  granular  germs  set  free 
from  the  blood,  along  with  the  matter  of  the  fibrinous  exudation  itself. 
215.  Besides  the  cells  already  mentioned,  the  blood  of  Yertebrated 
animals  also  contains  others,  which  are  distinguished  by  their  red  colour 
and  flattened  form.     These  are  equally  isolated,  and  lead  an  indepen- 


RED  CORPUSCLES  OF  BLOOD.  135 

dent  life ;  undergoing  all  their  changes  whilst  floating  in  the  rapidly- 
circulating  current.  These  Red  Corpuscles  can  scarcely  be  said  to 
exist  in  the  blood  of  Invertebrated  animals,  and  their  proportion  in  the 
blood  of  Vertebrata  varies  considerably  in  the  several  groups  of  that 
sub-kingdom ;  they  are  altogether  wanting  in  the  blood  of  the  Amphi-^ 
oxus  or  Lancelet,  which,  although  essentially  a  Fish,  has  many  pecu- 
liarities that  connect  it  with  the  lower  divisions  of  the  Animal  series. 
They  present,  in  every  instance,  the  form  of  a  flattened  disk,  which  is 
circular  in  Man  and  in-  most  Mammalia  (Front.  Fig.  1),  but  which  is 
oval  in  Birds,  Reptiles,  and  Fishes,  and  in  a  few  Mammals  [Front.  Fig. 
6).  This  disk  is  in  both  instances  a  flattened  cell,  whose  walls  are  pel- 
lucid  and  colourless,  but  whose  contents  are  coloured.  Like  the  cor- 
puscles already  described,  they  may  be  caused  to  swell  up  and  burst, 
by  the  imbibition  of  water  ;  and  the  perfect  transparency  and  the  homo- 
geneous character  of  their  walls  then  become  evident.  {Front.  Fig.  8, 
e.) — These  Red  Corpuscles  are  not  only  distinguished  from  the  others 
by  the  colour  of  their  contents ;  they  are  also  characterized  by  the  ab- 
sence of  the  separate  molecules,  which  formed  so  distinctive  a  feature 
in  the  preceding;  and  in  Oviparous  Vertebrata  by  the  presence  of  a 
distinct  central  spot  or  nucleus,  which  appears  to  be  composed  of  an 
aggregation  of  minute  granules,  analogous  to  those  elsewhere  diff'used 
through  the  interior  of  the  cell.  The  nucleus  (where  it  exists)  may  be 
easily  obtained  separate  from  the  cell-wall  and  its  contents,  by  treating 
the  red  corpuscles,  with  water.  The  first  efi'ect  of  this  is  to  render  the 
nucleus  rather  more  distinct,. as  is  seen  by  contrasting  the  corpuscle 
which  has  been  thus  slightly  acted  on  [Frofit.  Fig.  8,  a),  with  the  un- 
altered coYipnscle  (Front.  Fig.  6)  of  the  same  animal.  After  a  short 
time,  the  corpuscle  swells  out  and  becomes  more  circular  (Front.  Fig. 
8,  h);  and  in  a  short  time  longer,  the  nucleus  is  seen,  not  in  the  centre 
of  the  disk,  but  near  its  margin  (Front.  Fig.  8,  c,  d).  Finally,  the  wall 
of  the  cell  ruptures ;  the  nucleus  and  its  other  contents  are  set  free ; 
and  whilst  the  colouring  matter  is  difi'used  through  the  surrounding 
fluid,  the  cell-walls  and  the  nuclei  are  separately  distinguishable.  (Front. 
Fig.  8,  e.) — It  is  remarkable,  however,  that  the  Red  corpuscles  of  the 
blood  of  Mammals  should  possess  no  obvious  nucleus ;  the  dark  spot 
which  is  seen  in  their  centre  (Front.  Fig.  1),  being  merely  an  efiect  of 
refraction,  in  consequence  of  the  double-concave  form  of  the  disk. 
When  the  corpuscles  are  treated  with  water,  so  that  their  form  becomes 
first  flat,  and  then  double-convex,  the  dark  spot  disappears ;  whilst,  on 
the  other  hand,  it  is  made  more  evident  when  the  concavity  is  increased 
by  the  partial  emptying  of  the  cell,  which  may  be  accomplished  by 
treating  the  blood-corpuscles  with  fluids  of  greater  density  than  their 
own  contents. 

216.  The  size  of  the  Red  Corpuscles  is  not  altogether  uniform  in  the 
same  blood ;  thus  it  varies  in  that  of  Man  from  about  the  l-4000th  to 
the  l-2800th  of  an  inch.  But  we  generally  find  that  there  is  an  ave^ 
rage  size,  which  is  pretty  constantly  maintained  among  the  difierent 
individuals  of  the  same  species ;  that  of  Man  may  be  stated  at  about 
l-3400th  of  an  inch.  The  round  corpuscles  of  the  Mammalia  do  not 
in  general  depart  very  widely  from  this  standard ;  except  in  the  case  of 


136  STRUCTURE   AND    ENDOWMENTS    OF   ANIMAL   TISSUES. 

the  Musk-Deer,  in  which  they  are  less  than  l-12000th  of  an  inch  in 
diameter.  It  is  in  the  Camel  tribe  alone  that  we  find  oval  corpuscles 
among  Mammals ;  these  have  about  the  same  average  length  as  the 
round  corpuscles  of  Man,  but  little  more  than  half  the  breadth. — In 
Birds,  the  corpuscles  are  occasionally  almost  circular ;  but  in  general 
their  diameters  are  to  each  other  as  1 J  or  2  to  1.  The  size  of  the  cor- 
puscles is  usually  greater  according  to  the  size  of  the  Bird ;  thus  among 
the  Ostrich  tribe,  the  long  diameter  is  about  l-1650th  of  an  inch,  and 
the  short  diameter  l-3000th ;  whilst  among  the  small  Sparrows,  Finches, 
&c.,  the  long  diameter  is  about  l-2400th,  and  the  short  frequently 
does  not  exceed  half  that  amount. — It  is  in  Reptiles  that  we  find  the 
largest  red  corpuscles ;  and  it  is  in  their  blood,  therefore,  that  we  can 
best  study  the  characters  of  these  bodies.  The  blood-disks  of  the  Frog, 
from  the  facility  with  which  they  may  be  obtained,  are  particularly 
suitable  for  the  purpose  ;  their  long  diameter  is  about  the  1-1 000th  of  an 
inch,  whilst  their  short  or  transverse  diameter  is  about  l-1800th.  The 
curious  Proteus,  Siren,  and  other  allied  species,  which  retain  their  gills 
through  their  whole  lives,  are  distinguished  by  the  enormous  size  of 
their  blood-disks.  The  long  diameter  of  the  corpuscles  of  the  Proteus 
is  about  l-337th  of  an  inch ;  they  are  consequently  almost  distinguisha- 
ble with  the  unaided  eye.  The  long  diameter  of  the  corpuscles  of  the 
Siren  is  about  l-435th  of  an  inch,  and  their  short  diameter  about  l-800th ; 
the  long  diameter  of  the  nuclei  of  these  corpuscles  is  about  1-lOOOth, 
and  the  short  diameter  about  l-2000th  of  an  inch, — so  that  the  nuclei 
are  about  three  times  as  long,  and  nearljfc  twice  as  broad,  as  the  entire 
human  corpuscles. 

217.  The  relation  between  the  White  or  Colourless  and  the  Red 
Corpuscles  of  the  Blood  can  only  be  determined  by  attentively  watching 
their  development,  and  tracing  them  through  all  the  stages  of  their 
growth.  Although  our  knowledge  on  this  subject  is  far  from  complete, 
yet  there  seems  much  reason  to  believe,  from  the  observations  of  Mr. 
Wharton  Jones  on  the  difierent  forms  of  blood-cells  presented  in  the 
several  classes  of  animals,  and  from  those  of  Mr.  Paget  and  other  phy- 
siologists on  the  several  gradations  of  structure  exhibited  in  the  blood- 
cells  of  Mammalia,  that  the  red  corpuscles  have  their  origin  in  the 
colourless^  and  that  the  diff'erent  forms  of  blood-cell  presented  in  diffe- 
rent groups  of  animals  are,  in  fact,  progressive  stages  in  the  same  de- 
velopmental process,  which  may  be  checked  at  any  one  of  them. — Thus 
among  the  lower  Invertebrata,  the  cells  which  are  observed  to  float  in 
their  circulating  fluid,  seem  to  be  little  else  than  aggregations  of  gra- 
nules, presenting  a  tuberculated  surface ;  no  cavity  can  be  distinguished ; 
and  it  is  with  difficulty  that  the  presence  of  a  distinct  cell-wall  can  be 
demonstrated.  This  form,  which  is  designated  by  Mr.  Wharton  Jones 
as  the  "coarse  granule-cell,"  presents  itself  also  among  the  chyle  and 
lymph-corpuscles  of  Vertebrated  animals,  and  is  occasionally  met  with 
in  their  blood. — In  other  Invertebrata,  the  blood-cell  undergoes  a  fur- 
ther development ;  for  the  cell-wall  becomes  more  distinct,  and  the  gra- 
nules are  so  much  more  minute  as  to  give  to  the  entire  cell  a  somewhat 
nebulous  aspect,  its  surface  being  now  smooth  instead  of  tuberculated. 
This  form  of  corpuscle,  also,  termed  by  Mr.  Wharton  Jones  the  "  fine 


RED  CORPUSCLES  OF  BLOOD.  137 

granule-cell,"  is  found  in  the  chjle  and  lymph,  and  occasionally  in  the 
blood,  of  Vertebrated  animals. — The  next  stage  in  the  history  of  deve- 
lopment, is  the  aggregation  of  the  granules  into  a  distinct  nucleus^  and 
the  clearing  up  of  the  general  cavity  of  the  cell ;  and  thus  is  formed 
the  "  colourless  nucleated  cell,"  which  is  the  highest  grade  that  the- 
blood-cell  attains  in  the  Invertebrated  series ;  the  number  of  such  cells 
being  greater  in  each  class,  the  closer  is  its  approximation  to  the  Ver- 
tebrated sub-kingdom.  This  phase  presents  itself  also  in  the  blood  of 
Yertebrata,  as  a  transition  stage  between  the  chyle-  and  lymph-corpus- 
cle, and  the  proper  blood-disk  or  red-corpuscle. — Thus,  then,  we  see 
that  the  cells  -which  are  found  in  the  circulating  fluid  of  Invertebrated 
animals,  correspond  rather  with  those  of  the  Chyle  and  Lymph  of  Yer- 
tebrata, than  with  those  which  are  characteristic  of  the  Blood  of  the 
latter. 

218.  The  next  stage  of  development  seems  to  consist  in  the  acquire- 
ment of  the  peculiar  red  colour ;  and  in  the  change  of  form,  from  the 
spherical  to  the  flattened  or  discoidal.  Thus  is  produced  the  ""  coloured 
nucleated  cell,"  which  is  the  characteristic  grade  of  the  blood-disk  of 
the  Oviparous  Yertebrata  in  general.  This  grade  may  be  occasionally 
seen  in  the  blood  of  the  adult  Mammal,  as  the  transition-stage  between 
the  colourless  nucleated  cell,  and  the  non-nucleated  cells  which  are 
proper  to  it ;  but  it  is  more  easily  made  out  in  the  blood  of  the  em- 
bryo.— The  non-nucleated  red  corpuscles  which  are  characteristic  of 
Mammalia,  are  regarded  by  Mr.  Wharton  Jones  as  the  escaped  nuclei 
of  the  preceding,  which  have  undergone  development  into  cells;  but  it 
seems  much  more  probable,  that  they  are  the  same  cells  in  a  yet  more 
advanced  stage  of  development,  the  nuclei  having  been  absorbed,  as 
often  happens  in  the  case  of  other  cells. 

219.  There  can  be  no  doubt  that,  like  all  other  cells,  each  Blood- 
corpuscle  has  its  proper  term  of  life,  and  that  it  degenerates  and  dies 
when  this  is  expired ;  if  it  were  not,  therefore,  for  the  continual  pro- 
duction of  new  cells,  in  the  manner  just  described,  the  Blood  would 
soon  lose  its  due  proportion  of  these  components,  since  there  is  no 
reason  to  believe  that  the  fully-formed  red  corpuscle  can  regenerate  its 
kind,  although  multiplication  by  subdivision  may  take  place  in  an 
earlier  stage  of  its  development.  When  much  blood  has  been  drawn 
from  the  body,  the  proportion  of  red  corpuscles  in  the  remaining  fluid 
is  at  first  considerably  lowered ;  the  fluid  portion  of  the  blood  being 
replaced  almost  immediately,  whilst  the  floating  dells  require  time  for 
their  regeneration.  Their  amount  progressively  increases,  however, 
until  it  has  reached  its  proper  standard,  provided  that  a  due  supply  of 
the  materials  be  afibrded.  We  shall  presently  see  that  one  of  these 
materials  is  Iron  ;  and  it  is  well  known  that  iron  administered  internally 
is  an  important  aid  in  recovery  from  severe  hemorrhages,  as  well  as  a 
valuable  remedy  for  certain  constitutional  states,  in  which  there  is  a 
diminished  power  of  producing  red  corpuscles.  Thus  in  Chlorosis, 
under  the  administration  of  iron,  the  amount  of  red  corpuscles  in  the 
blood  has  been  doubled  within  a  short  period.  In  the  healthy  state  of 
the  system,  the  constant  production,  and  the  constant  death  and  disin- 
tegration, balance  one  another.     In  some  instances  (as  in  Chlorosis), 


138  STRUCTURE   AND    ENDOWMENTS   OF   ANIMAL   TISSUES. 

the  production  is  not  sufficient  to  make  up  for  the  loss  by  death ;  and 
the  total  amount  in  the  blood  undergoes  an  extraordinary  diminution, 
sometimes  even  to  less  than  a  quarter  of  their  proper  proportion.  In 
other  cases,  under  the  influence  of  excessive  nutriment  (as  in  the  state 
termed  Plethora),  the  proportion  of  Red  Corpuscles  is  increased  beyond 
the  normal  amount ;  and  in  this  condition,  the  loss  of  a  small  quantity 
of  blood  may  be  a  preservative  from  the  evils  to  which  it  is  incident, 
from  Hemorrhage  of  various  kinds. 

220.  The  Red  Corpuscles  make  their  first  appearance  in  the  blood 
of  the  Embryo,  however,  long  before  the  formation  of  chyle  and  lympl^ 
commences ;  and  they  appear  to  be  formed  by  the  metamorphosis  of 
some  of  the  cells  which  constitute  the  inner  layer  of  the  germinal  mem- 
brane (chap.  XI.)  These  cells  are  at  first  nearly  spherical,  ^nd  are 
full  of  particles  of  a  yellowish  substance  like  fatty  matter ;  in  the  midst 
of  which,  though  somewhat  obscured  by  them,  a  central  nucleus  may  be 
seen.  The  development  of  these  embryo-cells  into  the  oval  red  corpus- 
cles of  the  Oviparous  Vertebrata,  is  stated  by  Mr.  Paget  to  be  effected 
by  the  gradual  clearing-up,  as  if  by  division  and  liquefaction,  of  the 
contained  particles,  the  acquirement  of  the  blood-colour  and  of  the  ellip- 
tical form,  the  flattening  of  the  cell,  and  the  more  prominent  appearance 
of  the  nucleus.  This  first  set  of  blood-disks  is  nucleated  in  Mammalia, 
as  well  as  in  Oviparous  Vertebrata ;  and  they  occasionally  present  indi- 
cations of  being  in  course  of  multiplication  by  subdivision.  They 
gradually  disappear  from  the  blood,  however,  when  the  chyle  and 
lymph-corpuscles  first  present  themselves  in  the  circulating  current; 
and  thenceforth  the  Red  corpuscles  seem  to  be  formed  at  the  expense 
of  the  latter  alone.  It  is  curious  that  this  change  should  usually  coin- 
cide, in  the  Tadpole,  with  the  time  at  which  the  external  branchiae  dis- 
appear ;  and,  in  warm-blooded  animals,  with  the  period  at  which  the 
branchial  fissures  are  closed  in  the  neck,  and  the  course  of  the  circula- 
tion is  altered  (chap,  vi.) 

221.  The  chemical  composition  of  the  Red  Corpuscles  presents  cer- 
tain peculiarities  which  require  notice ;  that  of  the  White,  or  Colour- 
less, however,  has  not  been  specially  examined.  When  the  Red 
Corpuscles  are  separated  from  the  other  constituents  of  the  blood,  and 
are  treated  with  water,  their  contents  are  speedily  diffused  through  the 
fluid  (§  215) ;  and  from  this  may  be  abstracted  two  distinct  substances, 
which  are  designated  GlobuUne  and  Ilcematine.— The  former  does  not 
seem*to  differ  from  Albumen  in  any  greater  degree,  than  may  be  attri- 
buted to  the  presence  of  the  walls  and  nuclei  of  the  corpuscles,  from 
which  it  cannot  be  separated ;  and  it  is  probably  common  to  the  White, 
as  well  as  the  Red. — It  is  in  the  Red  alone,  however,  that  the  Hcematine 
exists.  The  composition  of  this  substance  is  notably  different  from  that 
of  the  proteine-compounds ;  the  proportion  of  carbon  to  the  other  ingre- 
dients being  very  much  greater ;  and  a  definite  quantity  of  iron  being 
an  essential  part  of  it.  Its  formula  is  44  Carbon,  22  Hydrogen,  3  Ni- 
trogen, 6  Oxygen,  and  1  Iron.  When  completely  separated  from  Albu- 
minous matter,  it  is  a  dark  brown  substance,  incapable  of  coagulation, 
nearly  insoluble  in  water,  alcohol,  ether,  acids,  or  alkalies,  alone ;  but 
readily  soluble  in  alcohol  mixed  either  with  sulphuric  acid  or  ammonia. 


uu 

i 


BED  CORPUSCLES  OF  BLOOD.  139 

The  solution,  even  wlien  diluted,  has  a  dark  colour ;  and  possesses  all 
the  properties  of  the  colouring  matter  of  venous  blood.  The  iron  may 
be  separated  from  the  hsematine  by  strong  reagents  which  combine  with 
the  former,  and  the  latter  still  possesses  its  characteristic  colour.  This 
hue  cannot  be  dependent,  therefore,  on  the  presence  of  iron  in  the  state 
of  peroxide ;  as  some  have  supposed.  On  the  other  hand,  the  iron  is 
most  certainly  united  firmly  with  the  ingredients  of  the  hgematine,  as 
contained  in  the  red  corpuscles ;  for  this  may  be  digested  in  dilute  sul- 
phuric or  muriatic  acid  for  many  days,  without  the  least  diminution  in 
the  quantity  of  iron,  the  usual  amount  of  which  may  be  afterwards  ob- 
tained by  combustion  from  the  haematine  that  has  been  subjected  to 
this  treatment.  This  experiment  seems  further  to  prove,  that  the  iron 
cannot  be  united  with  the  hgematine  in  the  state  of  either  protoxide  or 
peroxide,  as  maintained  by  Liebig ;  since  weak  acids  would  then  dissolve 
it  out.  Regarding  the  nature  of  this  compound,  and  the  changes  which 
it  undergoes  in  respiration,  there  is  still  much  to  be  learned ;  and  until 
these  points  have  been  more  fully  elucidated,  the  precise  uses  of  the 
Red  Corpuscles  in  the  animal  economy  cannot  be  understood.  There 
is  evidence,  however,  that  the  production  of  Hsematine  is  (like  the  pro- 
duction of  the  red  colouring  matter  of  the  Protococcus  nivalis,  §  26),  a 
esult  of  chemical  action  taking  place  in  the  cells  themselves ;  for  no 

bstance  resembling  Haematine  can  be  found  in  the  liquid  in  which 

ese  cells  float,  and  scarcely  a  trace  of  iron  can  be  detected  in  it; 

hilst,  on  the  other  hand,  the  fluid  portion  of  the  chyle  holds  a  large 
"quantity  of  iron  in  solution,  which  seems  to  be  drawn  into  the  red  cor- 
puscles, and  united  with  the  other  constituents  of  haematine,  as  soon  as 
ever  it  is  delivered  into  the  circulating  current. 

222.  It  has  been  usually  supposed,  until  recently,  that  the  diff'erence 
in  colour  between  Arterial  and  Venous  blood  is  due  to  different  states 
of  combination  of  the  Haematine  they  respectively  contain,  with  Oxygen 
and  Carbonic  acid.  For  in  its  passage  through  the  capillaries  of  the 
systenj,  the  arterial  blood  loses  its  bright  florid  hue,  and  assumes  the 
dark  purple  tint  which  distinguishes  ordinary  venous  blood ;  and  the 
converse  change  takes  place  in  the  capillaries  of  the  lungs,  the  original 
florid  hue  being  recovered.  Now  it  is  certain  that  the  blood,  in  its 
change  from  the  arterial  to  the  venous  condition,  loses  oxygen,  and 
becomes  charged  with  an  increased  amount  of  carbonic  acid,  although 
its  precise  mode  of  combination  is  not  known ;  on  the  other  hand,  in  its 
return  from  the  venous  to  the  arterial  state,  the  blood  gives  off  this 
additional  charge  of  carbonic  acid,  and  imbibes  oxygen.  The  change 
of  colour,  under  similar  conditions,  takes  place  out  of  the  body,  as  well 
as  in  it.  Thus  if  venous  blood  be  exposed  for  a  short  time  to  the  air, 
its  surface  becomes  florid ;  and  the  non-extension  of  this  change  to  the 
interior  of  the  mass  is  evidently  due  to  the  impossibility  of  bringing  air 
into  relation  with  every  particle  of  the  blood,  in  the  manner  which  the 
lungs  are  so  admirably  contrived  to  effect.  If  venous  blood  be  exposed 
to  pure  oxygen,  the  change  of  colour  will  take  place  still  more  speedily ; 
and  it  is  not  prevented  by  the  interposition  of  a  thick  animal  membrane, 
such  as  a  bladder,  between  the  blood  and  the  gas.  On  the  other  hand, 
i^rterial  blood  be  exposed  to  carbonic  acid,  it  loses  its  brilliant  hue, 


140  STRUCTURE   AND   ENDOWMENTS    OF   ANIMAL   TISSUES. 

and  is  rendered  as  dark  as  venous  blood ;  or  even  darker,  if  exposed 
very  completely  to  its  influence.  The  simple  removal  of  this  carbonic 
acid  is  not  sufficient  to  restore  the  original  colour ;  for  this  removal  may 
be  effected  by  hydrogen,  which  has  the  power  of  dissolving  out  (so  to 
speak)  the  carbonic  acid  diflfused  through  the  blood ;  but  the  arterial 
hue  is  not  restored  unless  oxygen  be  present,  or  saline  matter  be  added 
to  the  blood. — Recent  observations  seem  to  render  it  probable  that 
these  variations  are  due,  not  so  much  to  changes  of  composition  in  the 
Hasmatine,  as  to  changes  of  form  in  the  Corpuscles  which  contain  it. 
For  when  the  hsematine  has  been  separated  and  difi'used  through  water, 
it  is  neither  darkened  by  carbonic  acid,  nor  brightened  by  oxygen, 
unless  some  corpuscles  be  floating  in  the  solution.  And  it  appears 
that  the  efi*ect  of  oxygen,  like  that  of  saline  solutions,  is  to  contract  the 
corpuscles  and  to  thicken  their  walls,  thus,  by  altering  their  mode  of 
reflecting  light,  making  them  appear  bright  red ;  whilst  carbonic  acid, 
like  water,  may  be  seen  to  occasion  a  dilatation  of  the  corpuscle,  and 
a  thinning  of  its  walls  (which  are  at  last  dissolved  by  it),  in  a  degree 
that  is  probably  sufficient  to  account  for  the  darkening  of  the  hue  of 
the  mass. 

223.  These  changes  in  the  condition  of  the  Red  corpuscles  (whatever 
their  precise  nature  may  be),  taken  in  connexion  with  the  fact,  that 
these  bodies  are  almost  completely  restricted  to  the  blood  of  Vertebrata 
(whose  respiration  is  much  more  energetic  than  that  of  any  Invertebrated 
animals  save  Insects,  which  have  a  special  provision  of  a  diff'erent  cha- 
racter), and  that  their  proportion  to  the  whole  mass  of  the  blood  corre- 
sponds with  the  activity  of  the  respiratory  function, — leave  little  doubt 
that  they  are  actively  (but  not  exclusively)  concerned  as  carriers  of 
Oxygen  from  the  lungs  to  the  tissues,  and  of  Carbonic  acid  from  the 
tissues  to  the  lungs ;  and  that  they  have  little  other  direct  concern  in 
the  functions  of  Nutrition,  than  the  fulfilment  of  this  duty.  Their  com- 
plete absence  in  the  lower  Invertebrated  animals,  in  the  earliest  condi- 
tion of  the  higher,  and  in  newly-forming  parts  until  these  are  penetrated 
by  blood-vessels,  seems  to  indicate  that  they  have  no  immediate  con- 
nexion with  even  the  most  energetic  operations  of  growth  and  develop- 
ment ;  whilst,  on  the  other  hand,  there  is  abundant  evidence,  that  the 
normal  activity  of  the  animal  functions  is  mainly  dependent  upon  their 
presence  in  the  blood  in  due  proportion. 

224.  Next  in  independence  to  the  cells  or  corpuscles  floating  in  the 
animal  fluids,  are  those  which  cover  the  free  membranous  surfaces  of 
the  body,  and  form  the  Epidermis  and  Epithelium.  Between  these 
two  structures  there  is  no  more  real  difi'erence  than  there  is  between 
the  Skin  and  the  Mucous  membranes.  The  one  is  continuous  with  the 
other ;  they  are  both  formed  of  the  same  elements ;  they  are  cast  off 
and  renewed  in  the  same  manner ;  the  history  of  the  life  of  the  indivi- 
dual cells  of  each  is  nearly  identical ;  but  there  is  an  important  difi'e- 
rence in  the  purposes  which  they  respectively  serve  in  the  general  eco- 
nomy. The  Epidermis  or  Cuticle  covers  the  exterior  surfaces  of  the 
body,  as  a  thin  semitransparent  pellicle,  which  is  apparently  homoge- 
neous in  its  texture,  is  not  traversed  by  vessels  or  nerves,  and  was 
formerly  supposed  to  be  an  inorganic  exudation  from  the  surface  of  the 


I 


SIMPLE   ISOLATED    CELLS — EPIDERMIS. 


141 


trne  s"kin,  designed  for  its  protection.  It  is  now  known,  however,  to 
consist  of  a  series  of  layers  of  cells,  which  are  continually  wearing  off 
at  the  external  surface,  and  are  being  renewed  at  the  surface  of  the 
true  skin  ;  so  that  the  newest  and  deepest  layers  gradually  become  the 
oldest  and  most  superficial,  and  are  at  last  thrown  off  by  slow  desqua- 
mation. Occasionally  this  desquamation  of  the  cuticle  is  much  more 
rapid ;  as  after  Scarlatina  and  other  inflammatory  affections  of  the 
Skin. 

225.  In  their  progress  from  the  internal  to  the  external  surface  of 
the  Epidermis,  the  cells  undergo  a  series  of  well-marked  changes. 
When  we  examine  the  innermost  layer,  we  find  it  soft  and  granular ; 
consisting  of  nuclei^  in  various  stages  of  development  into  cells,  held 
together  by  a  tenacious  semi-fluid  substance.  This  was  formerly  consi- 
dered as  a  distinct  tissue,  and  was  supposed  to  be  the  peculiar  seat  of  the 
colour  of  the  skin ;  it  received  the  designation  of  rete  mucosum.  Passing 
outwards,  we  find  the  cells  more  completely  formed ;  at  first  nearly  sphe- 
rical in  shape ;  but  becoming  polygonal  where  they  are  flattened  against 
one  another.  As  we  proceed  further  towards  the  surface,  we  perceive 
that  the  cells  are  gradually  more  and  more  flattened,  until  they  become 
mere  horny  scales,  their  cavity  being  obliterated ;  their  origin  is  indi- 
cated, however,  by  the  nucleus  in  the  centre  of  each.  This  flattening 
appears  to  result  from  the  gradual  desiccation  or  drying  up  of  the  con- 
tents of  the  cells,  which  result  from  their  exposure  to  the  air.  Thus 
each  cell  of  the  Epidermis  is  developed  from  the  nucleus  on  the  surface 
of  the  basement-membrane — which  nucleus  is  probably  furnished  by  the 
membrane  itself  (§  208), — and  is  gradually  brought  to  the  surface  by  the 
development  of  new  cells  beneath,  and  the  removal  of  the  superficial 
layers ;  whilst  at  the  same  time  it  is  progressively  changed  in  form, 
until  it  is  converted  into  a  flattened  scale.     The  accompanying  repre- 


Fig.  20. 


Fig.  21. 


Oblique  section  of  Epidermis,  showing  the 
progressive  development  of  its  component 
cells;— a,  nuclei,  resting  upon  the  surface 
of  the  cutis  vera  /;  these  nuclei  are  seen  to 
be  gradually  developed  into  cells,  at  6,  c,  and 
d;  and  the  cells  are  flattened  into  lamellae, 
forming  the  exterior  portion  of  the  epidermis 
ate. 


Horny  Epidermis,  from  conjunctiva  covering 
the  cornea;  a,  single  scales;  b.  single  lamina  of 
epithelium ;  below  is  seen  a  double  layer  of  the 


sentation  of  an  oblique  section  of  the  Epidermis,  exhibits  the  principal 
gradations  of  its  component  structures. 


graaations 


142  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

226.  The  Epidermis  covers  the  whole  exterior  surface  of  the  body ; 
not  excepting  the  Conjunctiva  of  the  eye,  on  which,  however,  it  has 
more  the  character  of  an  Epithelium,  and  the  Cornea,  on  which  it  par- 
ticipates in  the  horny  character  of  the  Epidermic  covering  (Fig.  21). 
The  continuity  is  well  seen  in  the  cast  skin  or  slough  of  the  Snake ;  in 
which  the  covering  of  the  front  of  the  eye  is  found  to  be  as  perfectly 
exuviated  as  that  of  any  part  of  the  body.  The  number  of  layers  varies 
greatly  in  different  parts ;  being  usually  found  to  be  the  greatest  where 
there  is  most  pressure  or  friction.  Thus  on  the  soles  of  the  feet,  par- 
ticularly at  the  heel  and  the  ball  of  the  great  toe,  the  Epidermis  is  ex- 
tremely thick ;  and  the  palms  of  the  hands  of  the  labouring  man  are 
distinguished  by  the  increased  density  of  their  horny  covering.  It 
would  seem  as  if  the  irritation  of  the  skin  stimulated  it  to  an  increased 
production  of  this  substance.  The.  Epidermic  membrane  is  pierced  by 
the  excretory  ducts  of  the  sweat-glands,  and  of  the  sebaceous  follicles, 
which  lie  in  the  true  skin  and  immediately  beneath  it ;  or  we  should 
rather  say  that  it  is  continuous  with  the  delicate  epithelial  lining  of 
these.  The  Nails  may  be  considered  as  nothing  more  than  an  altered 
form  of  Epidermis.  When  examined  near  their  origin,  they  are  found 
to  consist  of  cells  which  gradually  dry  into  scales ;  and  these  remain 
coherent  together.  A  new  production  is  continually  taking  place  in  the 
groove  of  the  skin,  in  which  the  root  of  the  nail  is  imbedded ;  and  pro- 
bably also  from  the  whole  subjacent  surface. 

227.  The  Epidermis,  when  analysed,  is  found  to  differ  from  the  pro- 
teine-compounds  in  its  composition ;  but  not  in  any  very  striking  de- 
gree. The  proportion  of  its  elements  is  considered  to  be  48  Carbon, 
39  Hydrogen,  7  Nitrogen,  17  Oxygen;  and  this  corresponds  exactly 
with  the  composition  of  the  substance  of  which  Nails,  Horn,  Hair,  and 
Wool  are  constituted.  It  seems  probable,  however,  that  the  cell-walls 
are  formed,  as  elsewhere,  of  Fibrine ;  and  that  the  horny  matter  is  a 
secretion  in  their  interior,  which  is  drawn  from  the  elements  of  blood 
during  their  growth  and  development. 

228.  The  Epidermis  appears  solely  destined  for  the  protection  of  the 
true  Skin;  both  from  the  mechanical  injury  and  the  pain  which  the 
slightest  abrasion  would  produce ;  and  from  the  irritating  effects  of  ex- 
posure to  the  external  air  and  of  changes  of  temperature.  We  perceive 
the  value  of  this  protectiouy  when  the  Epidermis  has  been  accidentally 
removed.  It  is  very  speedily  replaced,  however ;  the  increased  deter- 
mination of  blood  to  the  Skin,  which  is  the  consequence  of  the  irrita- 
tion, being  favourable  to  the  rapid  production  of  Epidermic  cells  on  its 
surface. 

229.  Mingled  with  the  Epidermic  cells  we  find  others  which  secrete 
colouring  matter  instead  of  horn ;  these  are  termed  Pigment-cells. 
They  are  not  readily  distinguishable  in  the  epidermis  of  the  White 
races,  except  in  certain  parts,  such  as  the  areola  around  the  nipple,  and 
in  freckles,  naevi,  &c.  But  they  are  very  obvious,  on  account  of  their 
dark  hue,  in  the  newer  layers  of  the  Epidermis  of  the  Negro  and  other 
coloured  races ;  and,  like  the  true  Epidermic  cells,  they  dry  up  and 
become  flattened  scales  in  their  passage  towards  the  surface,  thus  con- 
stantly remaining  dispersed  through  the  Epidermis,  and  giving  it  a  dark 


SIMPLE   ISOLATED   CELLS. — EPIDERMIS. 


143 


tint  when  it  is  separated  and  held  up  to  the  light.  In  all  races  of  men, 
however,  we  find  the  most  remarkable  development  of  Pigment-cells  on 
the  inner  surface  of  the  Choroid  coat  of  the  eye,  where  they  form  seve- 
ral layers,  known  as  the  Pigmentum  nigrum.  Here  they  have  a  very 
regular  arrangement ;  which  is  best  seen  where  they  cover  the  bleocL 
vessels  of  the  Choroid  coat  in  a  single  layer,  as  shown  in  Fig.  22. 

Fig.  22. 


W^Mm  ■WtP^'fM^^^ 


Fig.  23. 

• 


^ 


Mj 


Corpuscles  of  Pigment, 
magnified  300  diameters ; — 
a,  cell ;  ft,  nucleus. 


ment-cells,  where  they  cover,  a,  a,  a,  the  veins,  in  a  single  layer  :  6,  ^, 
ramifications  of  the  veins  near  the  ciliary  ligament,  covered  with  less 
regular  pigment-cells ;  c,  c,  spaces  between  the  vessels,  more  thickly 
covered  with  pigment-cells. 

When  examined  separately,  they  are  found  to  have  a  polygonal  form 
(Fig.  23,  a),  and  to  have  a  distinct  nucleus  (6)  in  their  interior.  The 
black  colour  is  given  by  the  accumulation,  within  the  cell,  of  a  number 
of  flat  rounded  or  oval  granules,  measuring  about  1-20, 000th  of  an  inch 
in  diameter,  and  a  quarter  as  much  in  thickness  ;  these,  when  separately 
viewed,  are  observed  to  be  transparent,  not  black  and  opaque ;  and  they 
exhibit  an  active  movement  when  set  free  from  the  cell,  and  even  whilst 
enclosed  within  it.  The  pigment-cells  are  not  always  of  a  simple 
rounded  or  polygonal  form  ;  they  sometimes  present  remarkable  stellate 
prolongations,  under  which  form  they  are  well  seen  in  the  skin  of  the 
Frog. — The  Chemical  nature  of  the  black  pigment  has  not  yet  been 
made  evident ;  it  has  been  shown,  however,  to  have  a  close  relation  with 
that  of  the  Cuttle-fish  ink  or  Sepia,  which  derives  its  colour  from  the 
pigment-cells  lining  the  ink-bag ;  and  to  include  a  larger  proportion  of 
Carbon  than  most  other  organic  substances, — everj"  100  parts  contain- 
ing 58J  of  this  element. 

230.  That  the  development  of  the  Pigment- cells,  or  at  least  the  for- 
mation of  their  peculiar  secretion,  is  in  some  degree  due  to  the  influence 
of  Light,  seems  evident  from  the  facts  already  mentioned  (§93).  To 
these  it  may  be  added,  that  the  new-born  infants  of  the  Negro  and  other 
dark  races  do  not  exhibit  nearly  the  same  depth  of  colour  in  their  skins, 
as  that  which  they  present  after  the  lapse  of  a  few  days ;  which  seems 
to  indicate  that  exposure  to  light  is  necessary  for  the  full  development 
of  the  characteristic  hue.  An  occasional  development  of  dark  pigment- 
cells  takes  place  during  pregnancy  in  some  females  of  the  fair  races ; 
thus  it  is  very  common  to  meet  with  an  extremely  dark  and  b^road  areola 


k 


144  STRUCTURE  AND   ENDOWMENTS   OP  ANIMAL   TISSUES. 

round  the  nipple  of  pregnant  women ;  and  sometimes  large  patches  of 
the  cutaneous  surface,  on  the  lower  part  of  the  body  especially,  become 
almost  as  dark  as  the  skin  of  the  Negro.  On  the  other  hand,  individuals 
are  occasionally  seen  with  an  entire  deficiency  of  pigment-cells,  or  at 
least  of  their  proper  secretion,  not  merely  in  the  skin,  but  in  the  eye ; 
such  are  termed  Albinoes ;  and  they  are  met  with  as  well  among  the 
fair,  as  among  the  dark  races.  The  absence  of  colour  usually  shows 
itself  also  in  the  hair ;  which  is  almost  white. 

231.  The  Epithelium  may  be  designated  as  a  delicate  cuticle,  covering 
the  free  internal  surfaces  of  the  body ;  and  apparently  designed,  in  some 
instances,  simply  for  their  protection ;  whilst  in  other  cases,  as  we  shall 
presently  find,  it  serves  purposes  of  far  greater  importance.  It  has  long 
been  known  that  the  Epidermis  might  be  traced  continuously  from  the 
lips  to  the  mucous  membrane  of  the  mouth,  and  thence  down  the  oesopha- 
gus into  the  stomach ;  and  that  in  the  strong  muscular  stomach  or  giz- 
zard of  the  granivorous  birds,  it  becomes  quite  a  firm  horny  lining. 
But  it  has  been  only  ascertain^ed  by  the  use  of  the  Microscope,  that  a 
continuous  layer  of  cells  may  be  traced,  not  merely  along  the  whole  sur- 
face of  the  mucous  membrane  lining  the  alimentary  canal,  but  likewise 
along  the  free  surfaces  of  all  other  Mucous  membranes,  with  their  pro- 
longations into  follicles  and  glands;  as  well  as  on  Serous  and  Synovial 
membranes,  and  the  lining  membrane  of  the  heart,  blood-vessels,  and 
absorbents.  The  Epithelial  cells,  being  always  in  contact  with  fluids, 
do  not  dry  up  into  scales  like  those  of  the  Epidermis ;  and  they  differ 
from  them  also  in  regard  to  the  nature  of  the  matter  which  they  secrete 
in  their  interior.  In  this  respect,  however,  the  Epithelial  cells  of  dif- 
ferent parts  are  unlike  one  another,  fully  as  much  as  any  of  them  are 
unlike  the  cells  of  the  Epidermis  ;  for  we  shall  find  that  all  the  secretions 
of  the  body  are  the  product  of  the  elaboration  of  Epithelium  cells ; 
and  consequently  there  are  as  many  varieties  of  endowment,  in  these 
important  bodies,  as  there  are  varieties  in  the  result  of  their  action. 

232.  The  Epithelium  covering  the  Serous  and  Synovial  membranes, 
and  the  lining  of  the  blood-vessels,  is  composed  of  flattened  polygonal 
cells  (resembling  those  shown  in  Fig.  23),  lying  in  apposition  with  each 
other,  so  as  to  form  a  kind  of  pavement ;  hence  this  form  is  termed  pave- 
ment- or  tessellated-^^iihoimm.  There  is  no  reason  to  believe  that  it 
possesses  any  active  endowments  in  these  situations ;  since  it  does  not 
appear  to  be  concerned  in  the  elaboration  of  any  peculiar  secretion.  It 
has  been  already  pointed  out  (§  196),  that  the  fluid  of  serous  membranes 
is  separated  from  the  blood  by  a  simple  act  of  mechanical  transudation 
(which  often  takes  place  to  a  great  extent  after  death) ;  the  walls  of  the 
blood-vessels  do  not  appear  to  be  concerned  in  forming  any  peculiar 
secretion ;  and  the  only  product  of  this  kind,  which  indicates  any  special 
endowment  in  the  epithelium-cells,  is  the  synovia,  which  is  probably 
elaborated  by  the  cells  covering  the  vascular  fringes  of  the  synovial 
membrane,  formerly  mentioned  (§  198).  The  cells  draw  it  from  the  blood, 
during  the  progress  of  their  growth,  form  it  as  a  secretion  within  them- 
selves, and  then  cast  it  into  the  general  cavity  of  the  joint  (when  their 
term  of  individual  life  is  ended),  either  by  the  rupture  or  the  liquefac- 
tion of  their  walls.  In  other  cases,  it  would  seem  as  if  the  epithelial 
cells  were  not  frequently  cast  ofl"  and  renewed,  but  possessed  a  considera- 


SIMPLE  ISOLATED   CELLS. — EPITHELIUM. 


145 


le  permanency.  It  is  to  be  remembered  that,  in  the  healthy  state  of 
the  serous  and  synovial  membranes,  and  in  that  of  the  lining  membrane 
of  the  blood-vessels  and  absorbents,  they  are  entirely  secluded  from 
sources  of  irritation  ;  and  that  they  lead  a  sort  o^ passive  life,  very  dif- 
ferent from  the  active  life  of  the  mucous  membranes.  In  fact,  it  woul4 
appear  to  be  the  sole  object  of  the  serous  membranes,  to  enclose  and 
suspend  the  viscera,  in  such  a  manner  as  to  allow  of  the  access  of  blood- 
vessels, nerves,  gland-ducts,  &c.;  and  at  the  same  time  to  permit  them 
the  required  freedom  of  motion,  and  to  provide  against  the  irritation  of 
opposing  parts,  by  furnishing  an  extremely  smooth  and  moistened  sur- 
face, wherever  friction  takes  place.  Hence  we  find  membranes,  with  all 
the  characters  of  serous  surfaces;  in  the  false  joints-  formed  by  ununited 
fractures,  and  in  other  similar  situations. 

233.  The  Epithelium  of  the  Mucous  membranes  and  their  prolonga- 
tions, is  found  under  two  principal  forms,  the  tessellated,  and  the  ci/lin- 
drical.  An  example  of  the  Tessellated  form  is  shown  in  Fig.  24,  which 
shows  the  separate  epithelium  cells  of  the  mucous  membrane  of  the  mouth, 
as  they  are  frequently  met  with  in  saliva.  The  cells  are  not  always  so 
polygonal  in  form,  however  ;  sometimes  retaining  their  rounded  or  oval 
form,  and  being  separated  by  considerable  interstices,  so  that  they  can 
scarcely  be  said  to  form  a  continuous  layer.  A  specimen  of  this  kind 
is  seen  in  Fig.  25,  which  represents  a  group  of  epithelium  cells  from  one 
of  the  smaller  bronchial  tubes.  This  form  of  tessellated  epithelium  is 
more  commonly  met  with,  where  the  secreting  operations  are  more  active, 
the  life  of  the  cells  consequently  shorter,  and  the  renewal  of  them  more 
frequent ;  so  that  they  have  not  time,  so  to  speak,  to  be  developed  into 
a  more  continuous  layer.  The  Cylinder-Epithelium  is  very  differently 
constituted.  Its  component  cells  and  cylinders,  which  are  arranged  side 
by  side ;  one  extremity  of  each  cylinder  resting  upon  the  basement-mem- 


Fig.  25. 


Separated  Epithelium-cells,  a, 
with  nuclei,  b,  and  nucleoli,  c, 
from  mucous  membrane  of 
mouth. 


Pavement-Epithelium  of  the 
Mucous  Membrane  of  the 
smaller  bronchial  tubes;  a, 
nuclei  with  double  nucleoli. 


brane,  whilst  the  other  forms  part  of  the  free  surfjice.  The  perfect 
cylindrical  form  is  only  shown,  when  the  surface  on  which  the  cylinders 
rest  is  flat  or  nearly  so.  When  it  is  convex,  the  lower  ends  or  basfes  of 
the  cells  are  of  much  smaller  diameter  than  the  upper  or  free  extremi- 
ties ;  and  thus  each  has  the  form  of  a  truncated  cone,  rather  than  of  a 
cylinder.  (Fig.  26).  This  is  well  seen  in  the  cells,  which  cover  the  villi 
of  the  intestinal  canal.  (Fig.  29).  On  the  oihex  hand,  where  the  cylin- 
der-epithelium lies  upon  a  concave  surface,  the  free  extremities  of  the 
oells  may  be  smaller  than  those  which  are  attached.     Sometimes  each 

10 


146  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

cylinder  is  formed  from  more  than  one  cell,  as  is  shown  by  the  nuclei  it 
contains ;  although  its  cavity  seems  to  be  continuous  from  end  to  end. 
And  occasionally  the  cj^linders  arise  by  stalk-like  prolongations,  from 

Fig.  26. 


Vibratile  or  ciliated  Epithelium;— a,  nucleated  cells,  resting  on  their  smaller  extremities;  b,  cilia. 

a  tessellated  epithelium  beneath.  The  two  forms  of  Epithelium  pass  into 
one  another  at  various  points ;  and  various  transitional  forms  are  then 
seen, — the  tessellated  scales  appearing  to  rise  more  and  more  from  the 
surface,  until  they  project  as  long-stalked  cells,  truncated  cones,  or  cylin- 
ders. 

234.  Both  these  principal  forms  of  Epithelial  cells  are  frequently 
observed  to  be  fringed  at  their  free  margins  with  delicate  filaments, 
which  are  termed  cilia  ;  and  these,  although  of  extreme  minuteness,  are 
organs  of  great  importance  in  the  animal  economy,  through  the  extra- 
ordinary motor  powers  with  which  they  are  endowed.  The  form  of  the 
ciliary  filaments  is  usually  a  little  flattened,  and  tapering  gradually  from 
the  base  to  the  point.  Their  size  is  extremely  variable  ;  the  largest  that 
have  been  observed  being  about  l-500th  of  an  inch  in  length,  and  the 
smallest  about  l-13000th.  When  in  motion,  each  filament  appears  to 
bend  from  its  root  to  its  point,  returning  again  to  its  original  state,  like 
the  stalks  of  wheat  when  depressed  by  the  wind  ;  and  when  a  number  are 
afiected  in  succession  with  this  motion,  the  appearance  of  progressive 
waves  following  one  another  is  produced,  as  when  a  wheatfield  is  agitated 
by  frequent  gusts.  When  the  ciliary  motion  is  taking  place  in  full 
activity,  however,  nothing  whatever  can  be  distinguished,  but  the  whirl 
of  particles  in  the  surrounding  fluid;  and  it  is  only  w^hen  the  rate  of 
movement  slackens,  that  the  shape  and  size  of  the  cilia,  and  the  manner 
in  which  their  stroke  is  made,  can  be  clearly  seen.  The  motion  of  the 
cilia  is  not  only  quite  independent  (in  all  the  higher  animals  at  least) 
of  the  will  of  the  animal,  but  is  also  independent  even  of  the  life  of  the 
rest  of  the  body  ;  being  seen  after  the  death  of  the  animal,  and  pro- 
ceeding with  perfect  regularity  in  parts  separated  from  the  body.  Thus 
isolated  epithelium  cells  have  been  seen  to  swim  about  actively  in  water, 
by  the  agency  of  their  cilia,  for  some  hours  after  they  have  been  detached, 
from  the  mucous  surface  of  the  nose ;  and  the  ciliary  movement  has 
been  seen  fifteen  days  after  death  in  the  body  of  a  Tortoise,  in  which 
putrefaction  was  far  advanced.  In  the  gills  of  the  River  Mussel,  which 
are  among  the  best  objects  for  the  study  of  it,  the  movement  endures 
with  similar  pertinacity. 

235.  The  purpose  of  this  ciliary  movement  is  obviously  to  propel 
fluids  over  the  surface  on  which  it  takes  place ;  and  it  is  consequently 
limited  in  the  higher  animals  to  the  internal  surfaces  of  the  body,  and 
always  takes  place  in  the  direction  of  the  outlets,  towards  which  it  aids 


lit 

m 


I 


SIMPLE   ISOLATED   CELLS. — EPITHELIUM.  147 

in  propelling  the  various  products  of  secretion.  The  case  is  different, 
however,  among  animals  of  the  lower  classes,  especially  those  inhabiting 
the  water.  Thus  the  external  surface  of  the  gills  of  Fishes,  Tadpoles, 
&c.,  is  furnished  with  cilia ;  the  continual  movement  of  which  renews 
the  water  in  contact  with  them,  and  thus  promotes  the  aeration  of  the 
blood.  In  the  lower  Mollusca,  and  in  many  Zoophytes,  which  pass  their 
lives  rooted  to  one  spot,  the  motion  of  the  cilia  serves  not  merely  to 
produce  currents  for  respiration,  but  likewise  to  draw  into  the  mouth  the 
minute  particles  that  serve  as  food.  And  in  the  free-moving  Animal- 
cules, of  various  kinds,  the  cilia  are  the  sole  instruments  which  they 
possess,  not  merely  for  producing  those  currents  in  the  water  which  may 
bring  them  the  requisite  supply  of  air  and  food,  but  also  for  propelling 
their  own  bodies  through  the  water.  This  is  the  case,  too,  with  many 
larger  animals  of  the  class  Acalephae  (Jelly-fish),  which  move  through 
the  water,  sometimes  w^ith  great  activity,  by  the  combined  action  of  the 
vast  numbers  of  cilia  that  clothe  the  margins  of  their  external  surfaces* 
In  these  latter  cases  it  would  seem  as  if  the  ciliary  movement  were  more 
under  the  control  of  the  will  of  the  animal,  than  it  is  where  it  is  con- 
cerned only  in  the  organic  functions.  In  what  way  the  will  can  influence 
it,  however,  it  does  not  seem  easy  to  say ;  since  the  ciliated  epithelium- 
cells  appear  to  be  perfectly  disconnected  from  the  surface  on  which  they 
lie,  and  cannot,  therefore,  receive  any  direct  influence  from  their  nerves, 
f  the  cause  of  the  movement  of  the  cilia  themselves,  no  account  can  be 
given;  they  are  usually  far  too  small  to  contain  even  the  minutest 
fibrillse  of  muscle  ;  and  we  must  regard  them  as  being,  like  those  fibrillse, 
organs  sui  generis,  having  their  own  peculiar  endowment, — which  is,  in 
the  higher  animals  at  least,  that  of  continuing  in  ceaseless  vibration, 
during  the  whole  term  of  the  life  of  the  cells  to  which  they  are  attached. 
The  length  of  time  during  which  the  ciliary  movement  continues  after 
the  general  death  of  the  body,  is  much  less  in  the  warm-blooded  than 
in  the  cold-blooded  animals ;  and  in  this  respect  it  corresponds  with 
the  degree  of  persistence  of  muscular  irritability,  and  of  other  vital 
endowments. 

236.  The  Tessellated-Epithelium,  as  already  mentioned,  covers  the 
Serous  and  Synovial  membranes,  the  lining  membranes  of  the  blood- 
vessels and  absorbents,  and  the  Mucous  membranes  with  their  glandular 
prolongations,  except  where  the  cylinder-epithelium  exists.  It  presents 
itself,  with  some  modifications  presently  to  be  noticed,  in  the  ultimate 
follicles  of  all  glands,  and  also  in  the  smaller  bronchial  tubes.  In  this 
latter  situation  it  is  furnished  with  cilia ;  and  these  are  also  found  on 
the  cells  of  the  tessellated  epithelium,  which  covers  the  delicate  pia  mater 
lining  the  cerebral  cavities.  The  Cylinder-Epithelium  commences  at 
the  cardiac  orifice  of  the  stomach,  and  lines  the  whole  intestinal  tube  ; 
and,  generally  speaking,  it  lines  the  larger  gland-ducts,  giving  place  to 
the  tessellated  form  in  their  smaller  ramifications.  A  similar  epithelium, 
furnished  with  cilia,  is  found  lining  the  air-passages  and  their  various 
offsets, — the  nasal  cavities,  frontal  sinuses,  maxillary  antra,  lachrymal 
ducts  and  sac,  the  posterior  surface  of  the  pendulous  velum  of  the  palate 
and  fauces,  the  eustachian  tubes,  the  larynx,  trachea,  and  bronchi, — 
becoming  continuous,  however,  in  the  finer  divisions  of  the  latter,  with 


148 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 


the  ciliated  pavement-epithelium.  The  upper  part  of  the  vagina,  the 
uterus,  and  the  fallopian  tubes,  are  also  furnished  with  a  ciliated  Cylin- 
der-Epithelium. The  function  of  the  cilia  in  all  these  cases  appears  to 
be  the  same ;  that  of  propelling  the  viscid  secretions,  which  would 
otherwise  accumulate  on  these_^  membranes,  towards  the  exterior  orifices, 
whence  they  may  be  carried  off. 

237.  The  simplest  office  which  the  Epithelium-cells  of  Mucous  mem- 
branes perform,  appears  to  be  that  of  elaborating  a  peculiar  secretion 
termed  Mucus  ;  which  is  destined  to  protect  them  from  the  contact  of 
air,  or  from  that  of  the  various  irritating  substances  to  which  they  are 
exposed,  in  consequence  of  their  peculiar  position  and  functions.  This 
Mucus  is  a  transparent  semifluid  substance,  distinguished  by  its  peculiar 
tenacity  or  viscidity.  It  is  quite  insoluble  in  water ;  but  is  readily  dis- 
solved by  dilute  alkaline  solutions,  from  which  it  is  precipitated  again  by 
the  addition  of  an  acid.  A  substance  resembling  Mucus  may  be  pro- 
duced from  any  fibrinous  exudation,  or  even  from  pus,  by  treating  it 
with  a  small  quantity  of  liquor  potassse.  The  secretion  of  Mucus,  like 
the  formation  of  Epidermis,  appears  to  take  place  with  an  activity  pro- 
portioned to  the  degree  of  irritation  of  the  subjacent  membrane.  On 
many  parts  of  the  mucous  surface,  a  sufficient  supply  is  afforded  by  the 
epithelium-cells  which  cover  it ;  but  in  other  situations,  especially  along 
the  alimentary  canal,  the  demand  is  much  greater,  and  it  is  probably 
supplied  not  merely  by  the  cells  of  the  surface,  but  by  those  lining  the 
crypts  or  follicles  which  are  formed  by  involutions  of  it. 

238.  The  Epithelium-cells,  which  are  thus  being  continually  renewed 
on  the  Mucous  surfaces,  commonly  seem  to  haVe  their  origin  in  the 
granular  germs  diffused  through  the  basement-membrane ;  but  it  is  dif- 
ferent in  regard  to  the  cells  of  the  follicles,  which  seem  rather  to  occupy 
their  cavity  than  merely  to  line  their  walls,  and  which  appear  to  be  in 
course  of  continual  production  from  a  germinal  spot,  or  collection  of  re- 
productive granules,  at  the  blind  extremity  of  the  follicle.  This  is  the 
case  in  the  ultimate  follicles  of  the  more  complex  glands  ;  which  may  be 
regarded  as  so  many  repetitions  of  the  simple  crypts  or  follicles  in  the 
substance  of  the  mucous  membranes ; — the  only  difference  being,  that 


Fig.  27. 


Fig.  28. 


Fig.  29. 


Two  follicles  from  the  liver  of  Carcinus 
manas  (Common  Crab),  with  their  con- 
tained secreting  cells. 


Ultimate  follicles  of  Mammary 
gland,  with  their  secreting  cells, 
a,  a;—b,  b,  the  nuclei. 


the  former  pour  their  secretion  into  a  branch  of  a  duct,  which  unites 
the  other  ramifications  to  form  a  trunk ;  and  this  trunk  conveys  them  to 
their  destination  in  some  cavity  lined  by  a  mucous  membrane ;— whilst 
the  simple  follicles  or  crypts  at  once  pour  forth  their  secretion  upon  the 


Secreting   cells 
Human  Liver;  a,  m 
cleus;  6,  nucleolus; 
oil-particles. 


SIMPLE    ISOLATED    CELLS. — SECRETING    CELLS.  149 

^nmce  of  the  membrane.  The  accompanying  figure  (27)  represents 
two  follicles  of  the  liver  of  the  Common  Crab,  which  are  seen  to  be  filled 
with  secreting  cells ;  it  seems  evident,  from  the  comparative  sizes  of 
these  cells  in  different  parts,  that  they  originate  at  the  blind  extremity 
of  the  follicle,  where  there  is  a  germinal  spot ;  and  that,  as  they  recede 
from  that  spot,  they  gradually  increase  in  size,  and  become  filled  with 
their  characteristic  secretion,  being  at  the  same  time  pushed  onwards 
towards  the  outlet  by  the  continual  new  growth  of  cells  at  the  germinal 
spot.  In  Fig.  28  are  shown  the  corresponding  ultimate  follicles  of  the 
Mammary  gland ;  filled,  like  the  preceding,  with  secreting  cells. 

239.  The  whole  of  the  acts,  then,  by  which  the  separation  of  the  dif- 
ferent Secretions  from  the  Circulating  fluid  is  accomplished,  really  con- 
sist in  the  growth  and  nutrition  of  a  certain  set  of  cells,  usually  covering 
the  free  surfaces  of  the  body,  both  internal  and  external,  or  lining  cavi- 
ties which  have  a  ready  communication  with  these  by  means  of  ducts  or 
canals.*  These  cells  differ  widely  from  one  another,  in  regard  to  the 
kind  of  matter  which  they  appropriate  and  assemble  in  their  cavities ; 
although  the  nature  of  their  walls  is  probably  the  same  throughout. 
Thus  we  find  biliary  matter  and  oil,  easily  recognisable  by  their  colour 
and  refracting  powder,  in  the  cells  of  the  liver;  milk  in  the  cells  of  the 
Mammary  gland ;  sebaceous  or  fatty  matter  in  the  cells  of  the  sebaceous 
follicles  of  the  skin  ;  and  so  on.  All  these  substances  are  derived  from 
the  blood ;  being  either  contained  in  it  previously,  or  being  elaborated 
from  its  constituents  by  a  simple  process  of  transformation, — as,  for 
example,  that  which  converts  the  albumen  of' the  blood  into  the  caseine 
of  milk.  Hence  they  may  be  considered  as  the  peculiar  aliments  of  the 
several  groups  of  cells  ;  whose  acts  of  nutrition  are  the  means  of  drawing 
them  off,  or  secreting  them,  from  the  general  circulating  fluid.  When 
they  have  attained  their  full  growth,  and  accomplished  their  term  of  life, 
their  walls  either  burst  or  dissolve  away,  and  thus  the  contents  of  the 
cells  are  delivered  into  the  cavity,  or  upon  the  surface,  at  which  they 
are  required.  Now  as  all  the  canals  of  the  glands  open  either  directly 
outwards  upon  the  surface,  or  into  cavities  which  communicate  with  the 
exterior,  it  is  evident  that  the  various  products  of  the  action  of  these 
epithelial  cells  must  be  destined  to  be  cast  forth  from  the  body.  This 
we  shall  find  to  be  the  case ;  some  of  them,  as  the  bile  and  urine,  being 
excretions,  of  which  it  is  necessary  to  get  rid  by  the  most  direct  channel ; 
whilst  others,  like  the  tears,  the  saliva,  the  gastric  fluid,  the  milk,  &c., 
are  separated  from  the  blood,  not  so  much  for  its  purification,  but  because 
they  are  required  to  answer  certain  purposes  in  the  economy. 

240.  Now  whilst  thus  actively  concerned  in  the  Nutritive  functions 
of  the  economy,  and  exercising  in  the  highest  degree  their  powers  of 
selection  and  transformation,  these  Secreting  cells  appear  to  have  nothing 
to  do  with  the  operation  of  Reproduction.  We  have  seen  that  they  do 
not  even  regenerate  themselves  ;  all  their  energies  being,  as  it  were,  con- 
centrated upon  their  own  growth ;  and  the  successive  production  of  new 
broods  of  them  being  provided  for  by  other  means.  Throughout  the 
organized  creation,  it  appears  to  be  necessary  that  the  true  act  of  Gene- 


WKk*  Th 

■ 


*  The  Synovial  secretion  is  perhaps  the  only  one  which  is  poured  into  a  closed  sac. 


150  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

ration  should  be  performed  by  the  reunion  of  the  products  of  two  dis- 
tinct orders  of  cells ;  the  coalescence  of  which  produces  a  germ,  that  is 
the  starting-point  of  a  new  organism ; — thus  differing  from  the  act  of 
Reproduction  by  gemmation  or  budding,  which  essentially  consists  in  an 
extension  or  out-growth  from  the  original  organism,  by  the  subdivision 
of  cells  in  the  manner  already  described  (§  212).  Among  the  lowest 
Cellular  Plants,  in  which  every  cell  is  apparently  similar  to  the  rest, 
this  operation  is  effected  by  the  "conjugation"  of  any  pair  (as  it  would 
seem)  of  the  cells  which  have  been  produced  by  multiplication  from  the 
original  germ.  But  in  all  the  higher  organisms,  both  Vegetable  and 
Animal,  we  find  that  certain  cells  are  set  apart  for  this  purpose ;  and 
that  there  is  an  obvious  distinction  between  the  "germ-cells,"  from 
within  which  the  germ  ultimately  makes  its  appearance,  and  the  "  sperm- 
cells,"  which  communicate  to  them  a  fertilizing  influence.  Still  in  the 
lower  tribes,  both  of  Plants  and  Animals,  we  find  that  "sperm-cells" 
and  "  germ-cells"  are  developed  in  the  midst  of  the  ordinary  tissues  of 
the  body;  and  it  is  only  as  we  ascend  the  scale,  and  find  the  principle 
of  division  of  labour  carried  out  in  other  ways,  that  we  meet,  as  in  Man, 
with  particular  organs  set  apart  for  their  evolution,  and  find  these  organs 
appropriate  respectively  to  distinct  individuals. 

241.  The  spermatic  cells  of  Man  are  developed  within  the  tubuli  of 
the  Testicle ;  where  they  appear  to  hold  exactly  the  same  relation  to 
the  membranous  walls  of  those  tubuli,  as  do  the  secreting  cells  to  the 
tubes  and  follicles  of  the  proper  Glands,  being,  in  fact,  the  representa- 
tives of  their  epithelial  cells  (Fig.  30,  a).  Each  of  these  developes  in  its 
interior  a  variable  number  of  secondary  cells,  or  "  vesicles  of  evolution  ;" 
and  within  every  one  of  these  is  produced  a  single  thread-like  body, 
dilated  at  one  extremity,  and  possessed  of  a  remarkable  self-moving 
power,  which  is  termed  a  Spermatozoa.  Sometimes  the  vesicles  of  evolu- 
tion remain  inclosed  within  the  parent-cell,  until  their  spermatozoa  have 
been  completely  developed,  and  have  been  set  free  by  their  rupture  (5) ; 

Fig.  30. 


Formation  of  Spermatozoa  within  seminal  ceUs;  a,  the  original  nucleated  cell;  b,  the  same  enlarged,  with 
the  formation  of  the  Spermatozoa  in  progress;  c,  the  Spermatozoa  nearly  complete,  but  still  enclosed  within 
the  cell. 

and  thus,  when  they  have  all  performed  their  office,  the  parent-cell  con- 
tains nothing  but  a  bundle  of  spermatozoa  (c),  whose  dispersion  takes 
place  as  soon  as  its  cell-wall  gives  way.  From  the  very  peculiar  motion 
they   possess,  the  Spermatozoa   were   long  regarded  qs  distinct  and 


SIMPLE  ISOLATED    CELLS. — REPRODUCTIVE    CELLS.  151 

[ependent  animalcules ;  it  is  now  generally  admitted,  however,  that 
they  have  no  more  claim  to  a  distinct  animal  character,  than  have  the 
ciliated  epithelia  of  mucous  membrane,  which  will  likewise  continue  in 
movement  when  separated  from  the  body.  Similar  bodies  are  formed 
by  all  the  higher  Cryptogamic  Plants ;  and  it  appears  from  late  re- 
searches that  their  office,  as  in  Animals,  is  to  fertilize  the  contents  of 
the  "germ-cells,"  with  which  their  self-moving  power  brings  them  into 
contact  (chap,  xi.)  It  is  a  curious  fact  that  the  seminal  cells,  in  which 
the  Spermatozoa  are  formed,  are  ejected  from  the  gland  in  certain  Crus- 
tacea, not  only  before  they  have  burst  and  set  free  their  Spermatozoa, 
but  even  long  before  the  development  of  the  Spermatozoa  in  their  inte- 
rior is  completed; — thus  affording  a  complete  demonstration  of  their 
independent  vitality. 

242.  The  "  germ-cells,"  in  like  manner,  are  very  commonly  developed 
among  the  lower  Animals  as  the  epithelia  of  the  tubes  or  follicles  which 
constitute  the  ovary ;  but  in  Man  and  the  higher  Animals,  the  ovary  is 
a  solid  organ,  and  the  germ-cells  are  developed  in  its  substance,  lying 
in  the  midst  of  the  dense  fibrous  tissue  which  forms  its  parenchyma. 
These  germ-cells,  which  are  known  as  "ovisacs,"  like  the  sperm-cells, 
develope  secondary  cells  or  ova  in  their  interior ;  each  ovisac,  however, 
producing  but  a  single  ovum.  The  ovum,  again,  contains  a  tertiary  cell, 
the  germiT^al  vesicle^  whose  contents  appear  to  mingle  with  those  of  the 
sperm-cell  in  the  act  of  fecundation,  so  that  the  fertilized  germ  is  the 
result ;  the  remaining  contents  of  the  ovum  being  the  nutritive  materials, 
at  the  expense  of  which  this  germ  undergoes  its  first  development 
(chap.  XI.) 

243.  We  now  proceed  to  a  class  of  cells,  which  are  equally  indepen- 
dent of  each  other,  which  begin  and  end  their  lives  as  cells,  without 
undergoing  any  transformation,  but  which  form  part  of  the  substance  of 
the  fabric,  instead  of  lying  upon  its  free  surfaces  and  being  continually 
cast  off  from  them.  Still  their  individual  history  is  much  the  same  as 
that  of  the  cells  already  noticed  ;  and  they  differ  chiefly  in  regard  to  the 
destination  of  their  products.  The  first  group  of  this  class  deserving  a 
separate  notice,  is  that  which  effects  the  introduction  of  aliment  into  the 
body  ;  of  those  kinds  of  aliment,  at  least,  which  are  not  received  in  solu- 
tion by  any  more  direct  means.  Along  the  greater  part  of  the  intestinal 
tube,  from  the  point  at  which  the  hepatic  and  pancreatic  ducts  enter  it, 
to  the  rectum,  we  find  the  mucous  membrane  furnished  with  a  vast  num- 
ber of  minute  tufts  or  folds,  by  which  its  free  surface  is  vastly  extended ; 
these  are  termed  villi.  They  may  be  compared  to  the  ultimate  root- 
fibres  of  trees,  both  in  structure  and  function.;  for  each  of  them  gives 
origin  to  a  minute  lacteal  or  chyle-absorbing  vessel,  which  occupies  its 
centre ;  whilst  it  also  contains  a  copious  network  of  blood-vessels  (Fig. 
10,  p.  127),  which  appears  likewise  to  participate  in  the  act  of  absorp- 
tion, by  taking  up  substances  that  are  in  complete  solution.  Now  at  the 
end  of  every  villus,  there  may  be  seen,  whilst  the  process  of  digestion 
and  absorption  is  going  on,  a  cluster  of  minute  opalescent  globules,  in 
the  midst  of  which  the  origin  of  the  lacteal  is  lost.  These  globules, 
whose  size  varies  from  1-lOOOth  to  l-2000th  of  an  inch,  are  composed 
of  a  milky  fluid,  which  is  evidently  the  same  with  that  which  is  found  in 


152 


STRUCTURE   AND    ENDOWMENTS   OP   ANIMAL   TISSUES. 


the  lacteals ;  and  it  is  maintained  by  Prof.  Goodsir,  who  first  brought 
them  into  notice,  that  these  globules  are  really  cells^  and  that  it  is  by 

Fig.  31^ 


Diagram  of  mucous  membrane  of  Jejunum,  when  absorption  is  not  going  on;  a,  epithelium  of  a  villus;  b, 
secreting  epithelium  of  a  follicle;  c,  c,  c,  primary  membrane,  with  its  germinal  spots  or  nuclei,  d,  d;  c,  germs 
of  absorbent  vesicles ;  /,  vessels  and  lacteals  of  villus. 

their,  growth  and  nutrition  that  the  milky  fluid,  or  chyle,  is  selected  from 
the  contents  of  the  digestive  cavity.  Their  function,  therefore,  would 
be  precisely  the  converse  of  that  of  the  secreting  cells  already  described ; 
whilst  the  history  of  their  individual  lives  is  the  same.  These  absorbent 
cells  draw  their  materials  from  the  fluid  in  the  digestive  cavity,  instead 
of  from  the  blood ;  and  when  they  burst  or  liquefy,  they  set  free  their 
contents  where  they  may  be  taken  up  by  a  lacteal  and  conveyed  into 
the  circulating  current,  instead  of  pouring  them  into  a  cavity  through 
which  they  will  be  shortly  expelled.  In  the  intervals  of  the  digestive 
process,  however,  the  extremities  of  the  villi  are  comparatively  flaccid ; 
and  instead  of  cells,  they  show  merely  a  collection  of  granular  particles 
(Fig.  31,  e),  which  are  considered  by  Prof.  Goodsir  to  be  cell-germs. 
There  is  considerable  doubt,  however,  whether  these  supposed  cells  are 
anything  else  than  oil-globules ;  and  whether  the  real  agents  in  the 
selection  of  chyle  are  not  the  epithelium-cells  covering  the  villus  (a), 
within  which  chylous-looking  globules  have  been  occasionally  seen,  when 
digestion  was  going  on. 

244.  Although  the  Mucous  membrane  of  the  intestinal  tube  is  the 
only  channel  through  which  insoluble  nutriment  can  be  absorbed  in  the 
completely  formed  Mammal,  and  the  only  situation,  therefore,  in  which 
we  meet  with  these  absorbent  cells,  there  are  other  situations  in  which 
similar  cells  perform  analogous  duties  in  the  embryo.  Thus  the  Chick 
derives  its  nutriment,  whilst  in  the  egg,  from  the  substance  of  the  yolk, 
by  absorption  through  the  blood-vessels  spread  out  in  the  vascular  layer 
of  the  germinal  membrane  surrounding  the  yolk  ;  which  vessels  answer 
to  the  blood-vessels  and  lacteals  of  the  permanent  digestive  cavity,  and 
are  raised  into  folds  or  villi  as  the  contents  of  the  yolk-bag  are  diminished. 
Now  the  ends  of  the  vessels  are  separated  from  the  fluid  contents  of  the 
yolk-bag,  by  a  layer  of  cells ;  which  seems  to  have  for  its  object  to  select 
and  prepare  the  materials  supplied  by  the  yolk,  for  being  received  into 
the  absorbent  vessels. 

245.  In  like  manner,  the  embryo  of  the  Mammal  is  nourished,  up  to 


ABSORBENT   CELLS. 


153 


le  time  of  its  birth,  through  the  medium  of  its  umbilical  vessels ;  the 
ramifications  of  which  form  tufts,  that  dip  down,  as  it  were,  into  the 
maternal  blood,  and  receive  from  it  the  materials  destined  to  the  nutri- 
tion of  the  foetus,  besides  eifecting  the  aeration  of  the  blood  of  the  latter, 
by  exposing  it  to  the  more  oxygenated  blood  of  the  mother.  Now  around 
the  capillary  loop  of  the  foetal  tuft,  there  is  a  layer  of  cells,  closely  re- 
sembling the  absorbent  cells  of  the  villi ;  and  these  are  enclosed  in  a  cap 
of  basement-membrane,  which  completes  the  foetal  portion  of  the  tuft, 
and  renders  it  comparable  in  all  essential  respects  to  the  intestinal  villus. 
It  is  again  surrounded,  however,  by  another  layer  of  membrane  and  of 
cells,  belonging  to  the  maternal  system  ; — the  derivation  and  arrange- 
ment of  which  will  be  explained  hereafter.     The  maternal  cells  (b,  Fig. 

|2),  may  be  regarded  as  the  first  selectors  of  nutriment  from  the  circu- 

Fig.  32. 


Extremity  of  a  placental  villus : — a,  external  membrane  of  the  villus,  continuous  with  the  lining  mem- 
brane of  the  vascular  system  of  the  mother ;  b,  external  cells  of  the  villus,  belonging  to  the  placental  decidua; 
c,  c,  germinal  centres  of  the  external  cells.;  d,  the  space  between  the  maternal  and  foetal  portions  of  the 
villus;  c,  the  internal  membrane  of  the  villus,  continuous  with  the  external  membrane  of  the  chorion;  /, 
the  internal  cells  of  the  villus,  belonging  to  the  chorion;  g,  the  loop  of  umbilical  vessels. 

lating  fluid  of  the  parent :  the  materials,  partially  prepared  by  them,  are 
poured  into  the  cavity  (d)  surrounding  the  extremity  of  the  tuft ;  and 
from  this  they  are  taken  up  by  the  foetal  cells  (/),  ^which  further  elabo- 
rate them,  and  impart  them  to  the  capillary  loop  [g)  of  the  umbilical 
vessels. 

246.  Thus  we  see  that  the  several  functions  of  Selection,  Absorption, 
Assimilation,  Respiration,  Secretion,  and  Reproduction,  are  performed 
by  the  agency  of  cells  in  the  Animal  as  in  the  Vegetable  kingdom, — in 
the  complex  Human  organism,  as  in  the  humblest  Cryptogamic  Plant  : 
the  only  difference  being,  that  in  the  latter  there  is  a  greater  division  of 
labour,  different  groups  of  cells  being  appropriated  to  different  functions, 
in  the  general  economy,  whilst  the  history  of  their  own  processes  of 
nutrition  and  decay  is  everywhere  essentially  the  ^ame.  Thus  we  have 
seen  that  the  Absorbent  cells,  at  the  extremities  of  the  intestinal  or  pla- 
cental villi,  select  and  draw  into  themselves,  as  the  materials  of  their 
own  growth,  certain  substances  in  their  neighbourhood ;  which  are  still 
as  much  external  to  the  tissues  of  the  body,  as  are  the  fluids  surrounding 
the  roots  of  plants.  Having  come  to  their  full  term  of  life,  they  give 
up  their  contents  to  the  absorbent  vessels,  which  carry  them  into  the 
general  current  of  the  circulation,  where  they  are  mingled  with  the  fluid 
previously  assimilated, — the  blood.  Whilst  passing  through  the  vessels, 
they  are  subjected  to  the  action  of  the  various  cells  (all  of  which  we  have 
seen  to  be  successive  phases  of  the  same  type)  which  float  in  the  circu- 
lating current;  and  by  these  they  seem  to  be  gradually  assimilated,  Or 


154  STRUCTURE   AND   ENDOWMENTS   OP   ANIMAL   TISSUES. 

converted  into  a  substance  of  a  more  directly  organizable  character. 
The  special  function  of  the  red  corpuscles  peculiar  to  Vertebrated  animals, 
though  not  yet  accurately  known,  seems  intimately  connected  with  the 
process  of  Respiration.  Next  we  have  various  groups  of  cells,  external 
to  the  vessels,  on  the  free  surfaces  of  the  body  ;  whose  office  it  is  to  draw 
from  the  blood  certain  materials,  which  are  destined  for  Secretion  or 
separation  from  it ;  either  for  the  sake  of  preserving  that  fluid  in  its  re- 
quisite purity,  or  for  answering  some  other  purpose  in  the  system. 
These  cells  grow  at  the  expense  of  the  substances  which  they  draw  into 
themselves  from  the  blood  ;  and  on  their  dissolution,  they  cast  forth  their 
contents  on  the  free  surfaces  communicating  with  the  exterior  of  the 
body,  to  which  they  are  in  time  conveyed.  And,  lastly,  we  have  a 
special  set  of  O-enerative  cells,  destined  in  the  one  sex  to  prepare  the 
germs  of  new  beings  ;  and  in  the  other  to  elaborate  a  product  essential 
to  their  fertilization. 

247.  The  cells  which  are  thus  the  active  instruments  of  the  Organic 
functions,  are  usually  produced  and  succeed  one  another  with  a  rapidity 
proportional  to  the  energy  of  those  functions,  though  the  causes  which 
influence  their  gronvth  and  decay  are  not  always  evident.  Thus  it  is 
certain  that,  cceteris  paribus,  the  rate  of  production  of  the  Secreting 
cells  depends  upon  the  abundance  of  the  materials  supplied  by  the  circu- 
lating current,  which  they  are  destined  to  eliminate  from  it.  But  this 
is  by  no  means  the  sole  condition  of  their  development ;  for,  as  we  shall 
see  hereafter,  these  materials  may  accumulate  unduly  in  the  blood, 
through  the  insufficient  activity  of  the  cells  which  are  destined  to  sepa- 
rate them  ;  whilst,  on  the  other  hand,  the  presence  of  certain  substances 
in  the  blood  appears  to  accelerate  their  production.  Of  these  stimuli, 
Mercury  is  one  of  the  most  powerful ;  and  we  have  continual  opportu- 
nities of  Avitnessing  its  efi*ects,  in  giving  an  increased  activity  to  the 
secreting  actions.  There  is  probably  not  a  gland  in  the  body,  which  is 
not  in  some  degree  influenced  by  its  presence  in  the  blood  ;  but  the  liver, 
the  kidneys,  the  salivary  glands,  and  the  glandulae  of  the  intestinal 
canal,  appear  to  be  those  most  afi'ected  by  its  stimulating  powers.  The 
action  of  the  glands,  in  other  words  the  development  of  the  secreting 
cells,  appears  to  be  influenced  by  mental  emotions ;  being  sometimes  accele- 
rated, and  sometimes  retarded,  through  their  agency.  This  is  especially 
the  case  in  regard  to  the  secretion  of  Milk,  Tears,  Saliva,  and  Gastric  juice. 
It  seems  probable  that  the  influence  thus  manifested  is  partly  exerted 
through  the  capillary  circulation,  which  is  known  to  be  powerfully  afi'ected 
by  mental  emotions,  as  in  the  acts  of  blushing  and  erection  ;  and  that  the 
increased  production  of  the  secretion  is  im^mediately  due  to  the  increased 
flow  of  blood  to  the  gland.  But  there  are  other  phenomena  which  show 
that  the  development  and  actions  of  the  secreting  cells  are  more  directly 
influenced  by  the  nervous  system ;  these  will  be  hereafter  considered 
(chap.  IX.) 

5.    Of  Cells  connected  together  as  permanent  constituents  of  the  Tissues. 

248.  We  now  pass  on  to  consider  those  Cells,  which  enter  as  compo- 
nent elements  into  the  solid  and  permanent  fabric  of  the  body,  and  which 


I 


CELLS    CONNECTED   TOGETHER   IN    SOLID   TISSUES.  155 


do  not  take  so  active  a  part  in  its  vital  operations.  These  we  shall  find 
to  be  usually  more  or  less  closely  connected  together,  either  by  a  general 
enveloping  membrane^  or  by  an  intercellular  substance^  which  is  inter- 
posed between  their  walls,  and  holds  them  together  by  its  adhesive 
properties. 

249.  The  presence  of  a  general  enveloping  membrane  (where  it  is  not 
a  secondary  formation)  appears  to  depend  upon  the  persistence  of  the 
original  cell-walls  ;  which,  instead  of  liquefying  or  thinning  away,  when 
distended  by  the  multiplication  of  cells  in  their  interior,  are  thickened  or 
strengthened  by  additional  nutrition.  Such  is  perhaps  the  case  with  the 
sacculi  in  which  the  cells  of  Adipose  tissue  ( §  257)  are  often  found  clustered 
together;  but  this  condition  is  usually  much  more  obvious  in  many 
tumours,  whose  development  depends  upon  an  abnormal  process  of  growth. 

250.  Where  such  enveloping  membranes  are  wanting,  we  frequently 
find  the  component  cells  of  the  permanent  tissues  of  Animals  (like  those 
of  the  higher  plants)  held  together  by  an  intercellular  substance  ;  which 
generally  presents  no  distinct  traces  of  organization ;  and  which  usually 
consists  of  Gelatine,  or  of  a  substance  allied  to  it  in  composition.  The 
proportion  of  this  substance  to  the  cells  may  vary  in  different  cases ;  and 
very  different  characters  may  thus  be  presented  by  a  tissue  made  up  of 
the  same  elements.  Thus  the  subjoined  figure  (33)  represents  a  portion 
of  one  of  the  animal  layers  included  between  the  calcareous  laminae  of  a 
bivalve  shell ;  in  which  we  see  on  the  one  side  a  number  of  nuclei  or 
incipient  cells,  scattered  through  a  bed  of  homogeneous  intercellular  sub- 
stance, and  bearing  but  a  very  small  proportion  to  it ;  whilst  the  opposite 
end  exhibits  a  set  of  polygonal  cells,  in  close  contact  with  each  other, 
the  intercellular  substance  being  only  represented  by  the  thick  dark 
lines,  which  mark  the  boundaries  of  the  cells,  and  which  are  rather 
thicker  at  the  angles  of  the  latter.  Between  these  two  extremes,  we 
observe  every  stage  of  transition. 

251.  The  presence  of  a  very  large  amount  of  intercellular  substance, 
through  which  minute  cells  are  scattered  at  considerable  intervals  (Fig. 
33,  a),  is  characteristic  of  various  forms  of  Cartilage ;  and  more  par- 
ticularly of  that  soft  semi-cartilaginous  structure,  of  whfch  the  Jelly-fish 
are  for  the  most  part  composed.  In  other  forms  of  cartilage,  we  find 
the  cells  more  developed,  and  in  closer  proximity  to  each  other,  the 
proportion  of  the  intercellular  substance  being  at  the  same  time  dimi- 
nished (as  seen  at  h  and  c,  Fig.  33) ;  but  it  is  not  often,  save  in  the 
embryonic  structures,  that  we  find  the  cells  in  such,  close  proximity,  and 
the  intercellular  substance  so  nearly  wanting,  as  at  d.  Such  examples 
do  occasionally  present  themselves,  however,  even  in  the  soft  tissues. 
Thus  the  chorda  dorsalis,  which  replaces  the  vertebral  column  in  the 
lowest  Fishes,  and  of  which  the  analogue  is  found  in  the  embryos  of  the 
higher  Yertebrata,  is  made  up  of  a  structure  of  this  kind  (Fig.  16), 
The  true  Skin  in  the  Short  Sun-fish,  is  replaced  by  a  similar  layer  of 
cellular  tissue,  which  extends  over  the  whole  body,  varying  in  thickness 
from  one-fourth  of  an  inch  to  six  inches.  And  in  the  Lancelot  (a  little 
fish  which  is  destitute  of  so  many  of  the  characters  of  a  Vertebrated 
animal,  that  its  right  to  a  place  in  that  division  has  been  doubted),  a 
considerable  portion  of  the  fabric  is  made  up  of  a  similar  parenchyma. 


156 


STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 


252.  Now  we  shall  find  that  one  method,  by  which  the  requisite  firm- 
ness and  solidity  are  given  to  the  animal  fabric,  consists  in  the  depo- 

Fig.  33. 


Portion  of  shell-membrane,  showing  the  origin  of  cells  in  the  midst  of  horny  intercellular  substance;  a, 
nuclei;  6,  incipient  cells ;  c,  the  same  further  advainced,  but  separated  by  intercellular  substance ;  d,  the, 
cells  become  polygonal  by  mutual  pressure. 

sition  of  earthy  substances  in  the  interior  of  such  cells,  by  a  peculiar 
secreting  action  of  their  own.  Thus  in  Shell,  we  find  them  completely 
filled  up  with  carbonate  of  lime  ;  and  in  the  enamel  of  Teeth  with  phos- 
phate of  lime.  When  this  is  the  case,  there  is  a  tendency  to  an  apparent 
coalescence  of  the  cells,  by  the  obliteration  of  their  partitions  ;  or  rather, 
perhaps,  by  the  removal  of  the  whole  intercellular  substance  from  between 
them,  the  actual  cell-walls  being  so  very  thin,  that  they  are  not  distin- 
guishable. The  incipient  stages  of  this  coalescence,  as  seen  in  another 
portion  of  th^  same  membrane  as  that  represented  in  the  last  figure,  are 
shown  in  Fig.  34.  At  a,  the  nucleated  cells  are  very  distinct ;  and  are 
separated  by  a  large  quantity  of  intercellular  substance.  At  h,  they 
approach  each  other  more  closely,  the  amount  of  intercellular  substance 
being  less ;  the  widest  intervals  are  seen  at  the  angles  of  the  cells.  At 
c,  the  approximation  is  much  closer ;  and  the  cell-walls  are  scarcely  dis- 
tinguishable at  the  points  where  they  come  into  immediate  contact. 
Proceeding  further,  we  observe  that  the  partitions  are  much  less  com- 
plete ;  so  that  the  originally  distinct  cellular  character  of  the  membrane 

Fig.  84. 


Portion  of  shell-membrane,  showing  the  gradual  coalescence  of  distinct  cells ;  at  a,  the  cells  separated  by 
intercellular  substance;  at  b,  the  partitions  are  thinner;  and  at  c,  they  almost  disappear. 

is  chiefly  indicated  by  the  bright  nuclei,  which  are  regularly  dispersed 
through  it,  and  by  the  triangular  dark  spots,  Avhich  show  the  remain's  of 


'^l( 


FUSIFORM   CELLS.  157 


e  intercellular  substance,  at  the  angles  where  three  cells  join  each 
other.  The  coalescence  may  be  traced  further  than  it  is  shown  to  do 
in  the  figure ;  so  that  if  it  were  not  for  the  evidence  afibrded  by  the 
transition-stages  here  represented,  it  would  be  difficult  to  prove  that  the 
membranous  layer  had  its  origin  in  cells.  __ 

253.  These  facts,  respecting  the  gradual  coalescence  of  cells,  explain 
not  merely  certain  appearances  presented  in  Tooth,  Shell,  &c.  (here- 
after to  be  described) ;  but  also  those  which  are  exhibited  by  the  Base- 
ment-membrane, as  already  detailed  (§  206). 

254.  There  is  no  evidence,  in  the  preceding  case,  that  the  cavities  of 
the  cells  coalesce  ;  and  there  is  no  reason  why  they  should  do  so.  But 
we  often  find  such  a  union,  where  the  production  of  a  continuous  tube 
is  required.  The  long  straight  open  ducts,  through  which  the  sap  of 
Plants  rises  in  the  stem,  are  unquestionably  formed  by  a  coalescence  of 
the  cavities  of  cells  of  a  cylindrical  form,  placed  regularly  end  to  end ; 
and  it  seems  probable  that  the  network  of  anastomosing  vessels,  through 
which  the  elaborated  sap  finds  its  way  to  the  various  parts  of  the  vege- 
table fabric,  is  formed,  in  like  manner,  by  the  coalescence  of  cells, 
arranged  obliquely  and  transversely  in  regard  to  one  another.  In  like 
manner,  the  capillary  Blood-vessels  of  Animals  are  usually  believed  to 
originate  in  rows  of  cells,  the  cavities  of  which  have  run  together  by  the 
obliteration  of  the  transverse  partitions ;  as  the  persistent  nuclei  of  such 
cells  may  be  occasionally  brought  into  view  in  the  walls  of  the  capilla- 
ries. And  the  same  appears  to  be  the  origin  of  the  tubular  fibres  of 
Muscular  and  Nervous  tissue,  which  contain  the  elements  characteristic 
of  those  tissues ;  these  elements, — the  fibrillse  of  muscle  and  the  granular 
pith  of  the  nerve-tube, — being  evidently  the  secondary  products  of  parent- 
cells,  which  seem  to  remain  as  their  investing  tubuli,  in  the  walls  of 
which  the  original  nuclei  are  often  to  be  seen  (§  338  and  388). 

255.  Besides  these  changes,  the  original  cells  may  often  undergo 
marked  alterations  of  form  ;  and  this  quite  independently  of  any  pressure 
to  which  they  may  be  subject.  Thus  the  pigment-cells,  as  already  men- 
tioned (§  229),  frequently  exhibit  a  curious  stellate  form ;  arising  from 
the  development  of  radiating  prolongations,  which  are  put  forth  from 
the  original  spheroid.  A  form  which  is  frequently  assumed  by  the  cells 
that  are  developed  in  fibrinous  or  plastic  exudations,  and  which  is  also 
met  with  in  the  cells  of  tumours,  both  malignant  (or  Cancerous)  and 
non-malignant,  is  that  which  has  received  the  designation  oi  fusiform  or 
spindle-like,  from  its  prolonged  shape  and  pointed  extremites.  The 
A^arious  stages  of  transition,  which  may  be  observed  between  the  simple 
rounded  cell  and  the  fusiform  cell,  have  been  shown  in  Fig.  7 ;  and  it  is 
there  seen  that,  when  the  transformation  has  gone  to  its  utmost  extent, 
the  nucleus  of  the  cell  is  no  longer  visible,  so  that  it  bears  a  close  re- 
semblance to  a  simple  fibre.  Such  cells  are  found  amongst  the  simple 
fibrous  tissues ,  and,  in  the  opinion  of  many,  they  give  origin  to  them. 
The  appearance  of  tissue  composed  of  fusiform  cells,  is  shown  in  Fig.  35 ; 
this  is  seldom  met  with  as  a  permanent  part  of  the  normal  fabric ;  but 
it  is  a  frequent  product  of  morbid  action. 

256.  We  now  proceed  with  the  description  of  the  various  tissues  in 
the  Human  body,  which  are  composed  of  cells  united  or  transformed 


158 


STRUCTURE   AND   ENDOWMENTS   OF   ANIMAL   TISSUES. 


in  the  foregoing  manner ;  and  we  shall  commence  with  Adipose  or 
Fatty  tissue,  which  may  be  considered  as  a  sort  of  link,  connecting  the 
permanent  tissues  with  those  which  are  more  actively  concerned  in  the 
processes  of  Nutrition,  Secretion,  &c. 


Fig.  35. 


Fig.  36. 


Fusiform  tissue  of  plastic 
exudations ;  a,  fusiform  bo- 
dies without  nuclei ;  b,  nu- 
cleated fusiform  ceils;  c, 
granular  intercellular  sub- 
stance. 


Areolar  and  Adipose  tissue;  a,  a, 
fat-cells;  6,  b,  fibres  of  areolar 
tissues. 


257.  The  Adipose  tissue  is  composed  of  isolated  cells,  which  have  the 
power  of  appropriating  fatty  matter  from  the  blood,  precisely  in  the 
same  manner  as  the  secreting  cells  appropriate  the  elements  of  bile,  milk, 
&c.  These  cells  are  sometimes  dispersed  in  the  interspaces  of  the  Areolar 
tissue ;  whilst  in  other  cases  they  are  aggregated  in  distinct  masses, — 
constituting  the  proper  Adipose  tissue.  In  the  former  case  they  are 
held  in  their  places  by  fibres,  that  traverse  the  areolae  in  different  direc- 
tions ;  whilst  in  the  latter,  each  small  cluster  of  fat-cells  is  included  in 
a  common  envelope,  on  the  exterior  of  which  the  blood-vessels  ramify ; 
and  these  sacculi  are  held  together  by  areolar  tissue.  We  are  thus 
probably  to  regard  each  fatty  mass  in  the  light  of  a  gland,  or  assemblage 
of  secreting  cells,  penetrated  by  blood-vessels,  and  bound  together  by 
fibrous  tissue ;  but  having  its  follicles  closed  instead  of  open  (which 
appears  to  be  the  early  condition  of  the  follicles  of  all  glands,  §  238) : 
and  consequently  retaining  its  secretion  within  itself,  instead  of  pouring 
it  forth  into  a  channel  for  excretion! 


Capillary  network  around  Fat-cells. 


258.  The  individual  fat-cells  always  present  a  nearly  spherical  or  sphe- 
roidal form  ;  sometimes,  however,  when  they  are  closely  pressed  together. 


ADIPOSE  TISSUE.  159 

ie^t)ecome  somewhat  polyhedral,  from  the  flattening  of  their  walls 
against  each  other.  Their  intervals  are  traversed  by  a  minute  net-work 
of  blood-vessels  (Fig.  37),  from  which  they  derive  their  secretion ;  and 
it  is  probably  by  the  constant  moistening  of  their  walls  with  a  watery 
fluid,  that  their  contents  are  retained  without  the  least  transudation^ 
although  they  are  quite  fluid  at  the  temperature  of  the  living  body.  If 
the  Avatery  fluid  of  the  cell-walls  of  a  mass  of  Fat  be  allowed  to  dry  up, 
and  it  be  kept  at  a  temperature  of  100°,  the  escape  of  the  contained  oily 
matter  is  soon  perceptible. — By  this  provision,  the  fatty  matter  is  alto- 
gether prevented  from  escaping  from  the  cells  of  the  living  tissues,  by 
gravitation  or  pressure  ;  and  as  it  is  not  itself  liable  to  undergo  change 
when  secluded  from  the  air,  it  may  remain  stored  up,  apparently  unal- 
tered, for  almost  an  unlimited  period. 

259.  The  consistency,  as  well  as  the  Chemical  constitution,  of  the 
fatty  matter  contained  in  the  Adipose  cells,  varies  in  different  animals, 
according  to  the  relative  proportions  of  three  component  substances 
which  may  be  distinguished  in  it, — Stearine,  Margarine,  and  Oleine. 
The  two  former  are  solid  when  isolated,  and  the  latter  is  fluid ;  but  at 
the  ordinary  temperature  of  the  warm-blooded  animal,  they  are  dissolved 
in  it.  Of  these,  Stearine  is  the  most  solid ;  and  it  is  the  most  largely 
present,  therefore,  in  the  hardest  fatty  matter,  such  as  mutton-suet.  It 
is  crystalline  like  spermaceti ;  it  is  not  at  all  greasy  between  the  fingers, 
and  it  melts  at  143°.  It  is  insoluble  in  water,  and  in  cold  alcohol  and 
ether :  but  it  dissolves  in  boiling  alcohol  or  ether,  crystallizing  as  it 
cools.  The  substance  termed  Margarine  exists  along  with  stearine  in 
most  fats,  but  it  is  the  principal  solid  constituent  of  Human  fat,  and 
also  of  Olive  oil.  It  corresponds  with  Stearine  in  many  of  its  proper- 
ties, and  is  nearly  allied  to  it  in  Chemical  composition ;  but  it  is  much 
more  soluble  in  alcohol  and  ether,  and  it  melts  at  118°.  On  the  other 
hand,  Oleine,  when  pure,  remains  fluid  at  the  zero  of  Fahrenheit's  ther- 
mometer ;  and  it  is  soluble  in  cold  ether,  from  which  it  can  only  be 
separated  by  the  evaporation  of  the  latter.  It  exists  in  small  quantity 
in  the  various  solid  fats ;  but  it  constitutes  the  great  mass  of  the  liquid 
fixed  oils.  The  tendency  of  these  to  solidification  by  cold,  depends  upon 
the  proportion  of  stearine  or  margarine  they  may  contain. 

260.  All  these  substances  are  neutral  compounds  formed  by  the  union 
of  Stearic,  Margaric,  and  Oleic  acids,  respectively,  with  a  base  termed 
Glycerine  ;  this  base  may  be  obtained  from  any  fatty  matter,  by  treat- 
ing it  with  an  alkali,  which  unites  with  the  acid  'and  forms  a  soap, 
setting  free  the  Glycerine.  They  contain  no  Nitrogen ;  and  their  pro- 
portion of  Oxygen  is  extremely  small  in  comparison  with  their  amount 
of  Carbon  and  Hydrogen :  thus  Stearine  has  142  Carbon  and  141  Hy- 
drogen to  17  Oxygen :  and  in  the  other  substances  the  proportions  are 
similar.  The  fatty  bodies  appear  to  be  mutually  convertible  ;  thus  mar- 
garic acid  may  be  procured  from  stearic  acid,  by  subjecting  it  to  dry 
distillation ;  and  there  is  ample  evidence  that  animals  supplied  with  one 
of  them  may  produce  the  others  from  it. 

261.  Since  these  Fatty  matters  are  abundantly  supplied  by  the  Vege- 
table kingdom,  and  are  found  to  exist  largely  in  substances  which  were 
not  previously  supposed  to  contain  them,  it  is  not  requisite  to  suppose, 


,    noipre 


160  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

that  Animals  usually  elaborlite  them  by  any  transforming  process -from 
the  elements  of  their  ordinary  food..  The  mode  in  which  they  are  taken 
into  the  blood,  and  the  uses  to  which  they  are  subservient,  will  be  here- 
after investigated :  but  it  may  be  here  remarked,  that  the  portion  sepa- 
rated from  the  circulating  fluid  to  form  the  Adipose  tissue,  is  only  that 
which  can  be  spared  from  the  other  purposes,  to  which  the  fatty  matters 
have  to  be  applied.  Hence  the  production  of  this  tissue  depends  in  part 
upon  the  amount  of  Fatty  matter  taken  in  as  food ;  but  this  is  not  en- 
tirely the  case,  as  some  have  maintained ;  for  there  is  sufficient  evidence 
that  animals  may  produce  fatty  matter  by  a  process  of  chemical  trans- 
formation, from  the  starch  or  sugar  of  their  food,  when  there  is  an  uh- 
usual  deficiency  of  it  in  their  aliment. 

262.  The  development  of  Adipose  tissue  in  the  body  appears  to  an- 
swer several  distinct  purposes.  It  fills  up  interstices,  and  forms  a  kind 
of,  pad  or  cushion  for  the  support  of  moveable  parts ;  and  so  necessary 
does  it  seem  for  this  purpose,  that,  even  in  cases  of  great  emaciation, 
some  fat  is  alway-s  found  to  remain,  especially  at  the  base  of  the  heart 
around  the  origin  of  the  great  vessels^  and  in  the  orbit  of  the  eye.  It 
also  assists  in  the  retention  of  the  animal  temperature  by  its  non-con- 
ducting power ;  and  we  accordingly  find  a  thick  layer  of  it,  in  those 
warm-blooded  mammals  that  inhabit  the  seas, — either  immediately  be- 
neath their  skin,  or  incorporated  with  its  substance.  Its  most  important 
use,  however,  is  to  serve  as  a  reservoir  of  combustible  matter,  at  the 
expense  of  which  the  respiration  may  be  maintained  when  Other  mate- 
rials are  deficient ;  thus  we  find  that  the  respiration  of  hybernating 
animals  is  kept  up,  during  the  period  when  they  cease  taking  food 
(§  121),  by  the  consumption  of  the  store  of  fat  which  was  laid  up  in 
their  bodies,  previously  to  their  passing  into  that  state;  and  it  is  also 
to  be  noticed  that  herbivorous  animals,  whose  food  is  scanty  during  the 
winter,  usually  exhibit  a  strong  tendency  to  such  an  accumulation, 
during  the  latter  part  of  the  summer,  when  their  food  is  most  rich  and 
abundant,  in  order  to  supply  the  increased  demand  created  by  the  low 
external  temperature  of  the  winter  season.  Other  circumstances  being 
the  same,  it  appears  that  the  length  of  time  during  which  a  warm-blooded 
animal  can  live  without  food,  depends  upon  the  quantity  of  fat  in  its 
body;  for  the  rapid  lowering  of  its  temperature,  which  is  the  immediate 
cause  of  its  death  (§  117),  takes  place  as  soon  as  the  whole  of  this  store 
has  been  exhausted.  Of  the  means  by  which  the  fatty  secretion  is  taken 
back  again  into  the  current  of  the  circulation,  when  it  is  required  for 
use  in  the  system,  we  know  nothing  whatever. 

263.  In  order  that  it  may  be  applied  to  the  maintenance  of  the  ani- 
mal heat,  the  fatty  matters  must  be  received  back  into  the  blood ;  and 
although  we  have  no  certain  knowledge  of  the  mode  in  which  this  is 
accomplished,  yet  it  may  be  surmised  to  be  as  follows.  The  Blood  nor- 
mally contains  a  certain  amount  of  fatty  matter,  held  in  solution  by 
combination  with  its  alkali ;  and  should  this  be  exhausted  by  the  com- 
bustive  process,  the  circulating  current  will  draw  into  itself  a  fresh  sup- 
ply from  the  interior  of  the  fat-cells ; — it  having  been  shown  by  Mat- 
teucci  that  oleaginous  particles  will  pass  through  animal  membranes  by 


CARTILAGE.  161 

idosmose,  to  diffuse  themselves  through  an  aqueous  liquid,  provided 
the  latter  be  alkaline. 

264.  In  the  simpler  forms  of  Qartilage^  we  have  an  example  of  a  tissue 
of  remarkable  permanence,  composed  entirely  of  cells  scattered  through 
an  intercellular  substance.  This  substance  has  received  the  distin- 
guishing appellation  of  Qhondrine^  which  marks  it  as  the  solidifying" 
ingredient  of  Cartilage  (§177).  All  the  Cartilages  of  the  foetus, — those 
which  are  to  be  converted  into  bone,  as  well  as  those  which  are  to 
remain  unossified, — are  composed  of  it ;  and  yet,  as  soon  as  the  process 
of  Ossification  commences,  the  chondrine  is  replaced  by  Gelatine,  which 
is  the  sole  organic  constituent  of  the  animal  basis  of  bones.  The  per- 
manent cartilages,  however,  still  contain  only  Chondrine ;  but  if  acci- 
dental bony  deposits  should  take  place  in  them  (as  frequently  happens 
in  old  persons,  especially  in  the  cartilages  of  the  ribs),  the  Chondrine 
gives  place  to  Gelatine.  This  change  of  composition  is  coincident,  as 
we  shall  hereafter  see,  with  a  complete  change  in  texture ;  the  basis  of 
bony  tissue  not  being  Cartilage  (as  commonly  imagined),  but  consisting 
of  a  substance  much  more  nearly  allied  to  the  white  fibrous  tissue. — It 
is  only  in  the  pure  cellular  cartilages,  in  which  the  intercellular  sub- 
stance presents  no  trace  of  organization,  that  Chondrine  occurs.  Those 
of  the  ^5ro-cartilages  (§  269),  in  which  the  intercellular  substance  has 
the  characters  of  the  White  fibrous  tissue,  yield  gelatine  on  boiling,  in 
the  manner  of  the  ligaments  and  tendons ;  whilst  those  which  contain 
much  of  the  Yellow  or  elastic  tissue,  undergo  very  little  change  by  boil- 
ing, and  only  yield,  after  several  days,  a  small  quantity  of  an  extract 
which  does  not  form  a  jelly,  but  which  has  the  other  chemical  properties 
of  Chondrine. 

265.  Besides  the  organic  compounds  already  described,  most  Carti- 
•lages  contain  a  certain  amount  of  mineral  matter,  which  forms  an  ash 
when  they  are  calcined.  This  ash  contains  a  large  proportion  of  car- 
bonate and  sulphate  of  soda,  together  with  carbonate  of  lime,  and  a 
small  quantity  of  phosphate  of  lime ;  as  age  advances,  the  proportion 
of  the  soluble  compounds  diminishes,  and  the  phosphate  of  lime  predo- 
minates. This  is  especially  the  case  in  the  costal  cartilages,  which 
almost  invariably  become  converted  into  a  semi-ossified,  substance,  in 
old  persons  ;  and  it  is  remarkable  that,  even  before  they  have  themselves 
become  thus  condensed,  they  are  united  by  ossific  matter,  when  they 
have  undergone  fracture. 

Fig.  38.  ^ 


Cartilage  of  Mouse's  ear. 

When  a  pure  Cellular  Cartilage  is  examined  microscopically, 

11 


162  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

its  cells  are  seen  to  lie,  sometimes  singly,  and  sometimes  in  clusters  of  | 
two,  three,  or  four,  in  cavities  excavated  in  the  intercellular  substance. 
These  occur  at  very  variable  distances ;  for  in  some  instances  they  are 
packed  together  as  closely  as  the  cells  of  a  vegetable  parenchyma  (Fig. 
38);  whilst  in  others  the  principal  mass  is  composed  of  intercellular 
substance,  through  which  the  cells  are  interspersed  at  wide  intervals. 
From  the  various  appearances  which  may  be  observed  in  the  same  car- 
tilage, at  different  stages  of  its  growth,  it  would  appear  that  the  compo- 
nent" cells  multiply  by  the  doubling  process  already  described  (§  212) ; 
that  they  then  separate  from  one  another,  each  of  them  drawing  towards 
itself  (as  it  were)  an  envelope  of  intercellular  substance ;  and  that,  by 
the  repetition  of  the  same  process,  the  number  of  cells  in  the  cartilage 
may  be  indefinitely  multiplied. 

267.  Various  stages  of  this  history  are  shown  in  the  accompanying 
figure  (Fig.  39),  which  is  taken  from  a  section  of  the  cartilaginous  bran- 
chial ray  of  the  larva  or  tadpole  of  the  Rana  esculenta,  or  Edible  Frog. 
In  the  centre  of  the  figure  are  shown  three  separate  cells,  which  have 
evidently  been  at  one  time  in  closer  proximity  with  each  other.  In  one 
of  these  cells,  the  nucleus  is  seen  to  be  developing  two  new  cells  in  its 
interior  ;  and  a  continuation  of  this  process  would  give  rise  to  the  appear- 
ance shown  at  5,  where  two  cells  are  shown  in  close  contact,  being  evi- 
dently the  offspring  of  the  same  parent.  Now  if  each  of  these  cells  in 
like  manner  developes  two  others  within  itself,  a  cluster  of  four  will  be 
developed,  as  shown  at  a ;  and  after  a  time,  intercellular  substance  being 


Section  of  the  Branchial  cartilage  of  Tadpole ;  a,  group  of  four  cells,  separating  from  each  other ;  b,  pair 
of  cells  in  apposition;  c,  c,  nuclei  of  cartilage  cells;  d,  cavity  containing  three  cells. 

accumulated  around  each,  their  walls  will  separate,  and  they  will  acquire 
the  character  of  distinct  cells.  It  would  seem  as  if,  in  other  cases,  one 
of  the  first  pair  of  cells  developes  another  pair  in  its  interior,  whilst  the 
other  (from  some  unknown  cause),  does  not  at  once  proceed  to  do  so ; 
and  thus  only  three  cartilage-cells  instead  of  four  are  clustered  together 
in  the  cavity,  as  seen  at  d. 

268.  The  primitive  cellular  organization  now  described  is  retained  in 
some  Cartilages  through  the  whole  duration  of  their  existence.  This  is 
the  case,  for  example,  in  most  of  the  articular  cartilages  of  joints ;  in 
the  cartilaginous  portion  of  the  septum  narium,  in  the  cartilages  of  the 
alae  and  point  of  the  nose,  in  the  semilunar  cartilages  of  the  eyelids ;  in 
the  cartilages  of  the  larynx  (with  the  exception  of  the  epiglottis),  the 


CARTILAGE.  163 

cartilages  of  the  trachea  and  bronchial  tubes,  the  cartilages  of  the  ribs, 
and  the  ensiform  cartilage  of  the  sternum.  When  partial  ossific  depo- 
sits take  place,  it  is  usually  in  the  substance  of  cellular^  rather  than  in 
that  oi  fibrous  cartilage. 

269.  When  the  intercellular  substance,  instead  of  being  homogeneous^ 
has  a  fibrous  character,  the  tissue  called  Fihro-Cartilage  is  produced ; 
and  this  may  be  either  elastic  or  non-elastic,  according  as  the  yellow  or 
the  white  form  of  fibrous  structure  prevails.     In  some  instances,  the 
fibrous  structure  is  so  predominant  over  the  cellular,  that  the  tissue 

^^as  rather  the  character  of  a  ligament  than  of  a  cartilage.  The  white 
Jfebrous  structure  is  seen  in  all  those  cartilages,  which  unite  the  bones  by 
synchondrosis,  and  which  are  destined  not  merely  to  sustain  pressure, 
but  also  to  resist  tension.  This  is  the  case  especially  in  the  substances 
which  intervene  between  the  vertebrae,  and  which  connect  the  bones  of 
■bhe  pelvis;  these  in  adult  Man  are  destitute  of  cartilage-corpuscles,  ex- 
^Bept  in  and  near  their  centres ;  but  in  the  lower  Vertebrata,  and  in  the 
^nrly  condition  of  the  higher,  the  fibrous  structure  is  confined  to  the 
^Rxterior,  and  the  whole  interior  is  occupied  by  the  ordinary  cartilage- 
Hfcorpuscles.  The  yellow-fibrous  or  reticulated  structure  is  best  seen  in 
T  the  epiglottis,  and  in  the  concha  of  the  ear ;  in  the  former  of  these, 
'  scarcely  any  trace  of  cartilage-corpuscles  remains ;  and  in  the  latter, 
the  cellular  structure  is  only  to  be  met  with  towards  the  tip. 

270.  We  have  seen  that  the  elements  of  the  cellular  tissues  hitherto 
described,  do  not  come  into  direct  contact  with  the  blood-vessels.  The 
Epidermic  and  Epithelial  cells  are  separated  from  them  by  the  conti- 
nuous layer  of  basement-membraile,  which  forms  the  surface  of  the  true 
skin,  of  the  mucous  membranes,  of  the  glandular  follicles  produced 
from  them,  &c.  In  like  manner,  the  cells  of  Adipose  tissue  are  formed 
within  membranous  bags ;  around  which  the  blood-vessels  form  a 
minute  network.  The  cells  of  Cartilage  are  not  nourished  in  any 
more  direct  manner;  and  are  sometimes  at  a  considerable  distance  from 

Fig.  40. 


_^  Vessels  situated  between  the  attached  synovial  membrane,  and  the  articular  cartilage,  at  the  point 
where  the  ligamentum  teres  is  inserted  in  the  head  of  the  os  femoris  of  the  human  subject,  between  the 
third  and  fourth  months  of  foetal  life ;— a,  the  surface  of  the  articular  cartilage ;  h,  the  vessels  between 
the  articular  cartilage  and  the  synovial  membrane ;  c,  the  surface  to  which  the  ligamentum  teres  waa 
~**-iChed;  d,  the  vein;  6,  the  artery. 


e  nearest  vessels.  It  is  certain  that  the  substance  of  the  permanent 
cellular  Cartilages  is  not  permeated,  in  a  state  of  health,  even  by  the 
minutest  nutrient  vessels ;  none  such  being  brought  into  view  under  the 


164  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

highest  magnifying  power.  They  are,  however,  surrounded  by  vessels 
(Fig.  40),  which  form  large  ampullce  or  varicose  dilatations  at  their 
edges,  or  spread  over  their  surfaces  ;  and  it  is  by  the  fluid  which  is 
drawn  from  them  by  the  Cartilage-cells,  that  the  latter  are  nourished. 
The  nutrition  of  a  mass  of  Cartilage  thus  seems  to  bear  a  strong  resem- 
blance to  that  of  the  thick  fleshy  Sea-weeds,  which  are  in  like  manner 
composed  entirely  of  cells,  with  intercellular  substance  disposed  between 
them  in  greater  or  smaller  amount.  The  cells  in  nearest  proximity  to 
the  nutrient  fluid,  draw  from  it  the  requisite  materials,  and  transmit 
these  to  the  cells  in  the  interior  of  the  mass,  receiving  a  fresh  supply  in 
their  turn  from  the  source'  in  their  own  neighbourhood.  When  the  Ar- 
ticular or  other  cellular  Cartilages  are  inflamed,  however,  we  find  ves- 
sels passing  into  their  substance ;  but  these  vessels  are  formed  in  an 
entirely  new  tissuCj  which  is  the  product  of  the  inflammatory  process, 
and  cannot  be  said  to  belong  to  the  Cartilage  itself. 

271.  The  temporary  Cartilages,  which  have  a  like  cellular  structure, 
but  which  are  destined  to  undergo  metamorphosis  into  Bone,  are  equally 
destitute  of  vessels  when  their  mass  is  small ;  but  if  their  thickness  ex- 
ceed an  eighth  of  an  inch,  they  are  permeated  by  canals  for  the  trans- 
mission of  vessels.  Still  these  vessels  do  not  ramify  with  any  minute- 
ness in  the  'tissue;  and  they  leave  large  islets,  in  which  the  nutritive 
process  must  take  place  on  the  plan  just  described. 

272.  The  Fibro-Cartilages,  formed  as  it  were  by  the  intermingling  of 
two  distinct  elementary  structures,  have  a  degree  of  vascularity  propor- 
tioned to  the  amount  of  the  fibrous  tissue  which  they  contain  ;  but  these 
vessels  do  not  penetrate  the  cellular'  portions.  Adhere  such  are  distinct 
from  the  mixed  structure. 

273.  The  Cartilaginous  tissue  appears  to  be  more  removed  than 
almost  any  other  in  the  body  from  the  general  tide  of  nutritive  action. 
Its  properties  are  simply  of  a  physical  character ;  and  they  are  not  im- 
paired for  a  long  time  after  the  death  of  the  tissue,  its  tendency  to  de- 
composition being  very  slight,  so  long  as  it  is  exposed  to  ordinary  tem- 
peratures. It  is  protected  by  its  toughness  and  elasticity  from  those 
mechanical  injuries  to  which  softer  or  more  brittle  tissues  are  liable ; 
and  consequently  it  has  little  need  of  any  active  power  of  reparation. 
When  loss  of  substance  occurs  as  a  result  of  disease  or  accident,  this  seems 
never  to  be  repaired  by  real  cartilaginous  substance ;  but  the  space  is 
filled  up  by  a  fibrous  tissue  developed  from  the  reparative  blastema  (§  213). 
It  is  in  this  tissue  that  the  new  vessels  are  found,  which  have  been  erro- 
neously supposed  to  penetrate  the  cartilage  when  it  becomes  inflamed ; 
the  fact  being,  that  the  vessels  are  restricted  to  the  "false  membrane" 
formed  in  the  inflammatory  process,  which  takes  the  place  of  the  carti- 
laginous tissue  that  has  disappeared  in  consequence  of  imperfect  nutri- 
tion or  degeneration. 

274.  The  Cornea  of  the  Eye  bears  a  superficial  resemblance  to 
Cartilage;  but  it  corresponds  rather  with  Fibrous  Membranes  in  its 
elementary  structure.  Besides  its  anterior  or  conjunctival  layer,  which 
consists  of  epithelium,  and  its  posterior  layer  of  cells  constituting  the 
epithelium  of  the  aqueous  humour,  the  Cornea  has  been  shown  by  Mr. 
Bowman  to  consist  of  three  layers,  of  which  the  anterior  and  the  poste- 
rior (which  are  very  thin)  have  some  of  the  characters  of  the  yellow 


CELLS  CONNECTED  TOGETHER. — CORNEA. 


165 


elastic  tissue,  whilst  the  middle  one,  which  forms  its  principal  thick- 
ness, is  composed  of  white  fibres  interlaced  together  in  such  a  manner 

Fig.  41. 


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Nutrient  Vessels  of  the  Cornea;— A,  Superficial  vessels  belonging  to  the  Conjunctival  membrane,  and 
mtinued  over  the  margin  of  the  Cornea;  b,  Vessels  of  the  Sclerotic,  returning  at  the  margin  of  the  Cornea. 

as  to  form  numerous  lamellse,  their  interspaces  or  areolae  having  the 
form  of  tubes  regularly  arranged  and  constricted  at  intervals,  so  as 
not  to  be  unlike  rows  of  cartilage-cells,  for  which  in  fact  they  have  been 
mistaken. — Two  sets  of  vessels,  a  superficial  and  a  deep-seated,  surround 
the  margin  of  the  cornea.  The  former  (Fig.  41,  A,)  belong  rather  to 
the  Conjunctival  membrane,  which  forms  the  outer  layer  of  the  cornea ; 
and  they  are  prolonged  to  the  distance  of  l-8th  or  half  a  line  from  its 
margin,  then  returning  as  veins.  The  latter  (b)  do  not  pass  into  the 
true  Cornea,  but  terminate  in  dilatations  from  which  veins  arise,  just 
where  it  becomes  continuous  with  the  sclerotic.  In  diseased  conditions 
of  the  Cornea,  however,  both  sets  of  vessels  extend  themselves  through 
it.  Notwithstanding  the  absence  of  vessels  in  the  healthy  condition  of 
the  corneal  tissue,  incised  wounds  of  its  substance  commonly  heal  very 
readily,  as  is  well  seen  after  the  operation  for  Cataract ;  but  there  is  a 
danger  in  carrying  the  incision  around  a  large  proportion  of  its  margin, 
lest  the  tissue  should  be  too  much  cut  ofi"  from  the  supply  of  nutriment 
afi'orded  by  the  ampullae  of  the  vessels  that  surround  it. 

2T5.  The  Crystalline  Lens  of  the  Eye  approaches  Cartilage,  in  its 
structure  and  mode  of  nutrition,  more  nearly  than  any  other  tissue. 
It  may  be  separated  into  numerous  laminae;  which  are  composed  of 
fibres  that  lock  into  one  another,  by  their  delicately-toothed  margins. 
Each  of  these  fibres  appears  to  be  made  up  of  a  series  of  cells,  linearly 
arranged,  which  coalesce  at  an  early  period.  The  lens  is  not  per- 
meated by  blood-vessels ;  at  least  after  it  has  been  completely  formed ; 
these  being  confined  to  the  capsule.  During  the  early  part  of  foetal 
life,  and  in  ii;iflammatory  conditions  of  the  Capsular  membrane,  both 
its  anterior  and  its  posterior  portions  are  distinctly  vascular ;  but  at  a 
later  period,  only  the  posterior  half  of  the  Capsule  has  vessels  distri- 
buted  upon  its  surface.     It  has  been  shown  by  optical  experiments 


166  STRUCTURE  AND   ENDOWMENTS   OF   ANIMAL  TISSUES. 

devised  for  the  purpose,  that  a  moderate  vascularity  of  the  posterior 
capsule  does  not  interfere  with  distinct  vision ;  whilst  if  the  anterior 
capsule  were  traversed  by  vessels,  the  picture  on  the  retina  would  be 
no  longer  clear. — The  substance  of  which  the  lens  is  composed,  ap- 
pears to  be  soluble  Albumen,  or  perhaps  more  closely  resembles  the 
Globulin  of  the  blood. 

276.  The  Vitreous  body,  which  fills  the  greater  part  of  the  globe  of 
the  eye,  also  seems  to  possess  a  cellular  structure ;  the  cells  containing 
a  fluid,  which  is  little  else  than  water  holding  in  solution  a  small 
quantity  of  albumen  and  saline  matter ;  and  the  membrane  which  forms 
their  walls  being  so  pellucid  as  to  be  scarcely  distinguishable.  Indeed 
the  cellular  character  of  this  substance  is  chiefly  inferred  from  the  fact, 
that  when  its  capsule  or  enveloping  membrane  is  punctured,  even  in 
several  places,  the  contained  fluid  does  not  speedily  drain  away, — as 
it  would  do  if  it  were  merely  contained  in  the  interstices  of  an  areolar 
tissue.  The  blood-vessels  which  traverse  the  Vitreous  body  do  not 
send  branches  into  its  substance ;  and  it  must  derive  its  nutriment  from 
those  which  are  distributed  minutely  upon  its  general  envelope,  and 
probably  also  from  the  large  plexiform  vessels  of  the  ciliary  processes 
of  the  Choroid  coat. 

277.  Before  proceeding  to  describe  the  structure  of  Bone,  to  which 
it  seems  natural  to  pass  on  from  Cartilage,  it  will  be  useful  to  advert  to 
the  modes  in  which  the  tissues  of  Invertebrated  animals  are  consolidated 
by  deposits  of  solid  matter,  in  order  that  they  may  afibrd  the  requisite 
support  and  protection,  without  that  interstitial  growth  which  is  pecu- 
liar to  the  skeletons  of  the  Vertebrated  classes. — Commencing  with  the 
Polypifera,  or  Coral-forming  animals,  we  observe  that  their  strong  axes 
or  sheaths  are  destined  only  to  give  support  to  their  softer  structures, 
and  that  the  parts  once  consolidated  undergo  no  subsequent  change.  It 
was  formerly  imagined,  that  the  stony  Corals  were  "built  up"  by  the 
animals  which  form  them,  somewhat  in  the  same  manner  as  a  Bee  con- 
structs its  cell.  But  it  is  now  fully  demonstrated,  that  the  calcareous 
matter  (which  here  consists  solely  of  the  Carbonate  of  Lime)  is  combined 
with  the  living  tissue ;  and  that  the  most  solid  mass  of  Coral  thus  has 
an  organized  basis.  The  proportion  of  earthy  to  animal  matter,  how- 
ever, is  so  great  in  these  structures,  that  very  little,  if  any,  nutrient 
changes  can  take  place  in  their  tissues,  when  once  it  has  become  con- 
solidated. Such  changes  are  not,  however,  required.  The  substance 
thus  developed  by  the  attractive  pow-er  of  the  soft  gelatinous  tissues, 
which  draw  into  themselves  the  small  quantity  of  calcareous  matter  dis- 
solved in  the  surrounding  water,  is  so  little  disposed  to  undergo  change, 
that  it  will  maintain  its  solidity  for  centuries ;  and  even  when  acted  on 
by  water  or  by  heat,  it  does  not  undergo  disintegration,  for  its  calcareous 
particles  arrange  themselves  in  a  new  method,  and  become  converted 
into  a  solid  crystalline  rock.  Such  rocks,  the  product  of  the  metamor- 
phosis of  ancient  coral-formations,  make  up  a  large  proportion  of  the 
external  crust  of  the  earth.  The  solid  stem  or  sheath,  once  con- 
solidated, appears  to  undergo  no  further  change  in  the  living  Coral- 
structure  ;  for  its  increase  takes  place,  not  by  interstitial  but  by  super- 
ficial deposit, — that  is,  not  by  the  diffusion  of  new  matter  through  its 


I 


SHELLS   OF   MOLLUSCA. 


167 


whole  substance,  separating  from  each  other  the  parts  formerly  de- 
posited, but  by  the  mere  addition  of  particles  to  its  surface  and  extre- 
mities. In  this  manner  the  growth  of  a  solid  Coral-structure  may 
go  on  to  an  enormous  extent ;  the  surface  at  which  the  consolidating 
action  is  going  on,  being  the  only  part  alive,  that  is  exhibiting  any^ 
vital  change ;  and  all  the  rest  of  the  mass  being  henceforth  perfectly 
inert. 

278.  In  the  class  of  Echinodermata,  which  includes  the  Star-fish, 
Sea-Urchin,  &c.,  we  find  the  calcareous  structure  presenting  a  very 
elaborate  organization ;  as  an  example  of  this,  we  shall  select  the  shell 
of  the  Echinus,  commonly  known  as  the  Sea-Egg.  This  shell  is  made 
up  of  a  number  of  plates,  more  or  less  regularly  hexagonal,  and  fitted 
together  so  as  completely  to  enclose  the  animal,  except  at  two  points, 
one  of  which  is  left  open  for  the  mouth,  the  other  for  the  anus.  On 
the  surface  of  these  plates  are  little  tubercles,  for  the  articulation  of  the 
spines,  which  serve  as  instruments  of  defence  and  of  locomotion.  The 
substance  of  the  shell  and  of  the  spines  is  exactly  alike ;  being  a  sort,  of 
areolar  tissue,  consolidated  by  the  deposition  of  calcareous  matter,  and 
having  an  innumerable  number  of  interspaces  or  minute  cancelli,  freely 
communicating  with  each  other.  The  arrangement  of  this  calcareous 
network  in  the  spines  is  most  varied  and  elaborate ;  and  causes  thin 
sections  of  them  to  be  among  the  most  beautiful  of  all  microscopic  ob- 
jects. The  external  and  internal  surface  of  each  plate,  in  the  shell  of 
the  living  Echinus,  is  covered  with  a  membrane,  from  which  its  nutrition 

Fig.  42. 


ooc ^ 

O  O  o OOOOo'cTo  O  OjQy 

O-P  ooDOoo  o  9_2^ 

o  o  o  o  o       — 

ooooo/ 

OOOy 


Portion  of  the  shell  of  the  Echinus,  showing  at  a  the  constituent  plates,  and  at  6  the  calcified 
areolar  tissue,  of  which  they  are  composed. 

is  derived ;  this  membrane  dips  down  into  the  spaces  between  the  ad- 
jacent plates ;  but  it  does  not  penetrate  the  substance  of  the  plates 
themselves,  nor  does  it  transmit  vessels  to  their  interior.  A  simi- 
lar membrane  covers  and  encircles  the  spines;  and  it  also  connects 
these  with  the  shell,  being  continuous  with  the  membrane  that  envelopes 
the  latter.  Thus  each  plate  and  spine  is  itself  completely  extra-vascu- 
lar ;  but  it  is  enclosed  in  a  soft  membrane,  which  furnishes  (whether 
by  vessels  or  otherwise,  has  not  yet  been  ascertained),  the  elements  of 
its  nutrition. 

279.  But  we  do  not  here  find  any  evidence  of  interstitial  growth ; 
nor  is  there  any  reason  why  such  should  be  required.     For  the  tissue 


168  STRUCTURE  AND   ENDOWMENTS   OF   ANIMAL  TISSUES. 

of  which  it  is  composed,  although  of  such  extreme  delicacy,  is  of  greal^ 
permanence,  and  does  not  exhibit  the  slightest  tendency  to  decay,  how- 
ever long  it  is  preserved ;  so  that,  when  once  consolidated,  it  appears 
to  undergo  no  further  change  in  the  living  animal.  The  growth  of  the 
animal,  however,  requires  a  corresponding  enlargement  of  its  enveloping 
shell ;  and  this  is  provided  for  by  the  simple  process  of  superficial  de- 
posit, through  the  subdivision  of  the  whole  shell  into  component  plates. 
For  by  the  addition  of  new  matter  at  the  edge  of  each  plate,  by  the 
consolidation  of  a  portion  of  the  soft  membrane  that  intervenes  between 
the  adjacent  plates,  the  whole  shell  is  enlarged,  without  losing  its 
globular  form.  At  the  same.time  it  is  strengthened  in  a  corresponding 
degree,  by  the  consolidation  of  the  soft  tissue  at  the  surface  of  each 
plate.  And,  in  like  manner,  the  spines  are  enlarged  and  lengthened 
by  the  progressive  formation  of  new  layers,  each  on  the  exterior  of  the 
preceding ;  so  that  a  transverse  section  exhibits  a  number  of  concentric 
rings,  like  those  of  an  Exogenous  tree. — Thus  even  in  the  growth  of 
this  complex  and  elaborate  structure,  we  recognise  the  principle  of 
superficial  deposit,  which  we  shall  find  to  be  universal  amongst  the  hard 
parts  of  the  Invertebrata :  notwithstanding  that,  at  first  sight,  it  would 
have  appeared  impossible  to  provide  on  this  plan  for  the  gradual  en- 
largement of  a  globular  shell,  completely  enclosing  the  animal,  and 
therefore  required  to  keep  pace  with  the  latter  in  its  rate  of  increase. 

280.  Among  the  Mollusca,  we  find  the  body  sometimes  altogether 
destitute  of  solid  organs  of  support,  protection,  or  locomotion, — as  is  the 
case,  for  example,  in  the  Slug ;  and  the  movements  are  feeble  and  the 
habits  inert,  the  muscles  having  no  fixed  points  for  their  attachment, 
and  acting  without  any  of  the  advantages  of  leverage.  In  other  cases, 
we  find  the  body  more  or  less  completely  protected  by  a  Shell ;  which 
is  sufiiciently  large  in  some  instances  to  cover  the  body  completely, 
whilst  in  others  it  afi'ords  only  a  partial  investment.  The  plan  on  which 
this  shell  is  formed,  however,  is  very  different  from  that  which  has  just 
b6en  described;  being  much  less  complex.  The  Univalve  shells,  or 
those  formed  in  one  piece,  are  always  of  a  conical  form ;  the  cone  being 
sometimes  simple,  as  in  the  Limpet ;  in  other  cases  being  spirally  coiled,  , 
as  in  the  Snail.  Now  the  base  of  this  cone  is  open ;  and  through  this, 
the  animal  can  project  its  movable  parts.  When  its  increasing  size 
requires  additional  accommodation,  it  is  obvious  that  an  addition  to  the 
large  end  of  the  cone  will  increase  its  diameter  and  its  length  at  the 
same  time ;  so  as  to  afford  the  required  space,  without  any  alteration  in 
the  form  or  dimensions  of  the  older  and  smaller  portions  of  the  cone. 
This  last,  indeed,  is  frequently  quitted  by  the  animal,  and  remains 
empty ;  being  sometimes  separated  from  the  later  portions,  by  one  or 
more  partitions  thrown  across  by  the  animal, — as  is  seen  especially  in 
the  Nautilus  and  other  chambered  shells.  Besides  the  new  matter 
added  to  the  mouth  of  the  shell,  a  thin  layer  is  usually  formed  over  its 
whole  interior  surface ;  so  that  the  lining  of  the  new  part  is  continuous 
with  that  of  the  old. — In  the  Bivalve  shells,  we  trace  this  mode  of  in- 
crease without  any  difficulty ;  especially  in  such  shells  as  that  of  the 
Oyster,  in  which  the  successive  laminae  remain  distinct.  Each  lamina 
is  interior  to  the  preceding,  being  formed  on  the  living  surface  of  the 


SHELLS   OF   MOLLUSCA. 


169 


ttnimal ;  b]it  it  also  projects  beyond  it,  so  as  to  enlarge  the  capacity  of 
the  shell ;  and  as  the  separation  of  the  valves  affords  free  exit  to  those 
parts  of  the  animal,  which  are  capable  of  being  projected  beyond  the 
shell,  there  is  obviously  no  need  of  any  other  provision-  to  maintain  the 
shell  in  its  natural  form. — Thus  in  the  shells  of  the  Mollusca,  increase 
takes  place  at  the  surfaces  and  edges  only. 

281 .  The  proportion  of  organic  and  calcareous  matter  in  Shell  differs 
considerably  in  the  various  tribes.  The  former  is  sometimes  present  in 
such  small  amount,  that  it  can  scarcely  be  detected ;  and  the  condition 
of  the  calcareous  matter  then  obviously  approaches  that  of  a  crystalline 
deposit.  But  in  other  instances,  the  animal  basis  is  very  obvious; 
remaining  as  a  thick  consistent  membrane,  after  all  the  calcareous  mat- 
ter has  been  dissolved  away  by  an  acid.  This  membrane  is  formed  of 
an  aggregation  of  cells  arranged  with  great  regularity  (Fig.  43,  a) ;  the 
cavities  of  which  are  filled  with  carbonate  of  lime  in  a  crystalline  state. 


Fig.  43. 


I 


Prismatic  cellular  structure  of  shell  of  Pinna:— a,  surface  of  lamina;  b,  vertical  section. 

The  form  of  the  cells  approaches  the  hexagonal ;  their  diameter  varies 
in  different  shells  from  1-lOOth  to  l-2800th  of  an  inch  ;  their  thickness 
also  is  extremely  variable,  even  in  different  parts  of  the  same  shell. 
Thus  we  sometimes  meet  with  a  lamina  of  such  tenuity,  as  not  to  mea- 
sure 1-lOOth  of  an  inch  in  thickness,  whilst  in  other  instances,  a  single 
layer  may  have  a  thickness  of  half  an  inch,  or  even  (in  certain  large 
fossil  species)  of  an  inch  or  more.  In  this  case,  the  cells,  instead  of 
being  thin  flat  scales  like  the  tessellated-epitheliuiii  (§  233),  are  long 
prisms,  somewhat  like  the  cells  of  the  cylinder-epithelium  (Fig.  26), 
with  their  walls  flattened  against  each  other.  The  appearance  which  is 
then  presented  by  a  vertical  section  of  them,  is  represented  in  Fig.  43,  h: 
The  long  prismatic  cells  are  there  seen  to  be  marked  by  delicate  trans- 
verse striae,  and  these,  taken  in  connexion  with  other  indications,  appear 
to  show,  that  every  such  prism  is  in  reality  formed  by  the  coalescence 
of  a  pile  of  flat  cells,  resembling  those  which  are  seen  in  the  very  thin 
laminoe  just  described  ;  so  that  the  thickness  of  the  layer  depends  upon 
the  number  of  the  cellular  laminae  which  have  coalesced  to  form  its 
component  prisms.  This  character  is  of  interest,  as  representing  on  a 
Daagmfied  scale  a  corresponding  appearance  in  the  Enamel  of  human 


170  .  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

.  Teeth,  which  we  shall  presently  find  to  be  formed  upon  the  very  same 
plan  (§  318). 

282.  We  are  to  regard  this  kind  of  shell-substance,  therefore,  as 
formed  by  the  secreting  action  of  the  epithelial  cells  covering  the  mantle 
of  the  animal, — which  membrane,  though  it  answers  in  position  to  the 
skin,  has  the  soft,  spongy,  glandular  character  of  a  mucous  membrane. 
These  draw  calcareous  matter  into  their  cavities,  as  a  part  of  their  own 
process  of  growth :  this  matter  being  supplied  from  the  fluids  of  the 
vascular  surface  beneath.  Now  when  these  calcigerous  cells  are  sepa- 
rated by  intercellular  substance,  they  remain  distinct  through  the  whole 
of  their  lives,  and  they  form  by  their  cohesion  a  tenacious  membrane, 
that  retains  its  consistency  after  the  removal  of  the  calcareous  matter. 
But  this  is  only  the  case  in  certain  groups  of  shells,  chiefly  belonging  to 
the  bivalve  division.  When  the  intercellular  substance  is  wanting,  and 
the  cells  come  into  close  contact,  their  partitions  become  indistinct  on 
account  of  their  extreme  tenuity ;  and  not  unfrequently  a  fusion  of  the 
whole  substance  appears  to  take  place,  by  the  dissolution  of  the  original 
cell-walls,  so  that  it  becomes  more  or  less  homogeneous, — traces  of  the 
original  cellular  structure  being  here  and  there  distinguishable  (§  252). 

283.  Sometimes  where  this  fusion  has  taken  place,  so  as  to  obliterate 
the  original  cell-structure,  we  find  the  almost  homogeneous  substance 
traversed  by  a  series  of  tubuli,  not  arranged,  however,  in  any  very  defi- 
nite direction,  but  forming  an  irregular  network  (Fig.  44).  These  tubes 
vary  in  size  from  l-2000th  to  l-20,000th  of  an  inch;  but  their  general  diame- 
ter, in  the  shells  in  which  they  most  abound,  is  l-4500th  of  an  inch.  In 
the  larger  tubuli,  something  of  a  bead-like  structure  may  occasionally  be 
seen :  as  if  their  interior  were  occupied  by  rounded  granules  arranged 
in  a  linear  direction.  Although  it  might  be  supposed  that  this  structure 
is  destined  to  convey  nutrient  fluid  into  the  substance  of  the  shell,  yet 
there  is  no  evidence  that  such  is  the  fact ;  and,  on  the  contrary,  there  is 
ample  evidence  that,  even  in  sh  ells  most  copiously  traversed  by  these  tubuli, 
no  processes  of  interstitial  growth  or  renewal  take  place.  The  perma- 
nent character  of  the  substance  of  all  Shells,  when  once  it  is  fully  formed, 
is  as  remarkable  as  that  of  Coral :  and  as  the  adaptation  of  their  size. 


^^H 

^^R 

^r^^^^^S%^5^^^fc 

^^^H 

^s^^^^^^s 

^^^^^^HP 

^^H 

R^R^^^E 

^8 

m^^^^^B^ 

K 

Tubular  shell-structure,  from  Anomia. 


to  that  of  the  animals  to  which  they  belong,  is  entirely  effected  by  addi- 
tions to  their  surfaces  and  edges,  no  interstitial  deposit  can  have  a  share 
in  producing  it. 


SHELLS   OF   CRUSTACEA.  171 

!84.  Among  the  Articulated  classes,  we  still  find  that  the  skeleton  is 
altogether  external,  and  belongs  therefore  to  the  cutaneous  system  ;  but 
it  is  formed  upon  a  very  different  plan  from  the  shells  of  the  Mollusca, 
being  closely  fitted  to  the  body,  and  enveloping  every  part  of  it ;  conse- 
quently it  must  increase  in  capacity,  with  the  advancing  growth  of  the 
contained  structures.  Moreover  it  is  destined  not  merely  to  afford  sup- 
port and  protection  to  these,  but  to  serve  for  the  attachment  of  the  mus- 
cles by  which  the  body  and  limbs  are  moved :  and  the  hard  envelopes 
of  the  latter  serve,  like  the  bones  of  the  Yertebrata,  as  levers  by  which 
the  motor  powers  of  the  muscles  are  more  advantageously  employed. 
Again,  the  hard  envelopes  of  the  body  and  limbs  are  not  formed  of  dis- 
tinct plates,  like  those  of  the  Echinus-shell ;  but  are  only  divided  by 
sutures  at  the  joints,  for  the  purpose  of  permitting  the  requisite  freedom 
of  motion.  It  might  have  been  thought  that  here,  if  anywhere,  a  process 
of  interstitial  growth  would  have  existed,  to  adapt  the  capacity  of  the 
envelopes  to  the  dimensions  of  the  contained  parts,  as  the  latter  increase 
with  the  growth  of  the  animal ;  but,  true  to  the  general  principle,  that 
epidermic  structures  are  not  only  extra-vascular,  but  that  they  undergo 
no  change  when  they  are  once  fully  formed,  we  find  that  the  hard  enve- 
lopes of  Articulated  animals  are  thrown  off,  or  exuviated,  when  the  con- 
tained parts  require  an  increase  of  room ;  and  that  a  new  covering  is 
formed  from  their  surface,  adapted  to  their  enlarged  dimensions. 

285.  This  is  well  known  to  occur  at  certain  intervals  in  Crabs,  Lob- 
sters, and  other  Crustacea ;  which  thus  exuviate  not  merely  the  outer 
shell,  with  the  continuation  of  the  epidermis  over  the  eyes,  but  also  its ' 
internal  reflection,  which  forms  the  lining  of  the  oesophagus  and  stomach, 
and  the  tendinous  plates  by  which  the  muscles  are  attached  to  the  lining 
of  the  shell.  A  similar  moulting  may  be  observed  to  occur  in  some  of 
the  minute  Entomostracous  Crustacea  of  our  pools,  every  two  or  three 
days,  even  after  the  animals  seem  to  be  full  grown.  During  the  early 
growth  of  Insects,  Spiders,  Centipedes,  &c.,  a  similar  moult  is  frequently 
repeated  at  short  intervals ;  but  after  these  animals  have  attained  their 
full  growth,  which  is  the  case  with  Insects  at  their  last  change,  no  fur- 
ther moulting  takes  place,  the  necessity  for  it  having  ceased.  This 
moulting  is  precisely  analogous  to  the  exfoliation  and  new  formation  of 
the  Epidermis,  in  Man  and  most  other  Vertebrata ;  differing  from  it 
only  in  this,  that  the  latter  is  constantly  taking  place  to  a  small  extent, 
whilst  the  former  is  completely  effected  at  certain  intervals,  and  then 
ceases.  We  have  examples  of  a  periodical  complete  m/oult  in  Yertebrata, 
however,  among  Serpents  and  Frogs. 

286.  The  structure  of  the  hard  envelopes  of  Articulated  animals  cor- 
responds with  that  of  the  Epidermis  and  its  appendages  in  Man.  The 
firm  casings  of  Beetles,  for  example,  are  formed  of  layers  of  epidermic 
cells,  united  together,  and  having  their  cavities  filled  by  a  horny  secre- 
tion. The  densest  structure  is  found  in  the  calcareous  shells  of  the 
Crustacea;  which  consists  of  a  substance  precisely  analogous  to  the 
Dentine  of  Teeth  (§  311);  covered  on  the  exterior  with  a  layer  of 
pigment-cells.  The  calcareous  matter  consists  chiefly  of  carbonate 
of  lime ;  but  traces  of  the  phosphate  are  also  found.  The  animal  basis 
has  a  firm  consistent  structure,  resembling  that  of  teeth.     A  thin  ver- 


172  STRUCTURE  AND  ENDOWMENTS   OP  ANIMAL  TISSUES. 

tical  section  shows  the  tubuli  running  nearly  parallel,  but  with  occasional 
undulations,  from  the  internal  surface  towards  the  external;  but  no 
traces  of  the  original  calcigerous  cells  can  be  detected  in  the  fully-formed 
shell,  the  process  of  fusion  having  gone  so  far  as  to  obliterate  them. 
The  manner  in  which  these  tubuli  are  formed,  will  be  presently  con- 
sidered, under  the  head  of  Dental  substance. 

28T.  Now  the  condition  of  the  osseous  skeleton  of  Vertebrated  animals 
is  altogether  different.  Its  purpose  is  still  only  mechanical ;  its  sole  use 
being,  to  afford  support  and  protection  to  the  softer  textures,  and  to 
form  inflexible  levers  by  the  action  of  the  muscles,  upon  which  motion 
may  be  given  to  the  different  parts  of  the  fabric.  But  it  forms  a  part 
of  the  internal  substance  of  their  bodies ;  and  as  these  grow  in  every 
part,  and  not  merely  by  addition  to  this  or  that  portion,  so  must  the 
Bones  also,  in  order  to  keep  pace  with  the  rest  of  the  structure.  Hence 
we  find  them  so  formed,  that  the  processes  of  interstitial  deposition  may 
be  continually  going  on  in  their  fabric,  as  in  that  of  the  softer  tissues ; 
and  the  changes  in  their  substance  do  not  cease,  even  when  they  have 
acquired  their  full  size.  The  subsequent  continuance  of  these  changes 
appears  destined,  not  so  much  to  repair  any  waste  occasioned  by  decom- 
position,— for  this  must  be  very  trifling  in  a  tissue  of  such  solidity, — as 
to  keep  the  fabric  in  a  condition,  in  which  it  may  repair  the  injuries  in 
its  substance  occasioned  by  accident  or  disease.  The  degree  of  this 
reparative  power  is  proportional,  as  we  shall  presently  see,  to  the  activity 
of  the  normal  changes,  which  are  continually  taking  place  in  the  bone ; 
and  is  thus  much  greater  in  youth  than  in  middle  life,  and  greater  in 
the  vigour  of  manhood  than  in  old  age. 

288.  The  structure  of  Bones. is  well  adapted  to  demonstrate  the  dis- 
tinction between  the  tissues  themselves,  and  those  subsidiary  parts,  by 
which  they  are  connected  with  the  rest  of  the  fabric.     We  have  seen 
that  Cartilage  is  essentially  non-vascular  ;  that  is,  even  when  it  exists 
in  a  considerable  mass,  it  is  not  traversed  by  vessels,  but  is  nourished 
by  absorption  from  the  fluids  contained  in  the  vessels  distributed  on  its 
exterior.    Now  every  mass  of  Bone  is  penetrated  by  vessels ;  nevertheless 
these  do  not  penetrate  its  ultimate  substance,  and  may  be  easily  sepa- 
rated from  it,  leaving  the  bone  itself  as  it  was.     In  fact,  as  Prof.  Goodsir , 
observes,  "  a  well-macerated  bone  is  one  of  the  most  easily  made,  an( 
at  the  same  time  one  of  the  most  curious  anatomical  preparations.     I( 
is  a  perfect  example  of  a  texture  completely  isolated  ;  the  vessels,  nerveJ 
membranes,  and  fat,  are  all  separated,  and  nothing  is  left  but  the  non** 
vascular  osseous  substance."     Precisely  the  same  may  be  said  of  th( 
substance  of  a  Tooth,  from  which  the  vascular  lining  of  the  pulp-cavitj 
has  been  removed ;  for  it  then  possesses  neither  vessels,  nerves,  noi 
lymphatics  ;  and  yet,  as  we  shall  presently  see,  it  has  a  highly-organize( 
structure,  peculiar  to  itself. 

289.  The  general  characters  of  Osseous  texture  vary  according  to  the 
shape  of  the  Bone,  and  the  part  of  it  examined.  Thus  in  the  long  bonesi 
we  find  the  shaft  pierced  by  a  central  canal,  which  runs  continuously 
from  one  extremity  to  the  other ;  and  the  hollow  cylinder  which  sur-i 
rounds  this  is  very  compact  in  its  structure.  On  the  other  hand,  the 
dilated  ends  of  the  bone  are  not  penetrated  by  the  large  central  canal  i 


STRUCTURE   OF   BONE. 


173 


nor  are  they  composed  of  solid  osseous  substance.     They  are  made  up 
of  cancellated  structure,  as  it  is  termed ;  that  is,  of  osseous  lamellae  and 
fibres   interwoven   together   (like   those  of  areolar 
tissue,  on  a  larger  scale)  so  as  to  form  a  multitude  Fig.  45. 

;  of  minute  chambers  or  cancelU,  freely  communicating 
with  each  other,  and  with  the  cavity  of  the  shaft ; 
whilst  the  whole  is  capped  with  a  thin  layer  of  solid 
bone.     Again,  in  the  thin  flat  bones,  as  the  scapula, 

;  we  find  the  two  surfaces  composed  of  solid  osseous 

:  texture,  with  more  or  less  of  cancellated  structure 
interposed  between  the  layers.  And  in  the  thicker 
flat  bones,  as  the  parietal,  frontal,  &c.,  this  cancel- 

I  lated  structure  becomes  very  distinct,  and  forms  the 

!  diploe ;  this,  however,  is  sometimes  deficient,  leaving 

!  a  cavity  analogous  to  the  canal  of  the  long  bones : 

\  whilst  the  plates  which  form  the  surfaces  of  the  bone 

j  (the  external  and  internal  tables  of  the  skull),  re- 

I  semble  in  their  thickness  and  solidity,  as  well  as  in 

I  the  intimate  structure  presently  to  be  described,  the 

I  shaft  or  hollow  cylinder  of  those  bones.    Finally,  we 

;  frequently  meet  (especially  in  the  Ethmoid  and  Sphenoid  bones)  with 

j  thin  lamellae  of  osseous  substance,  resembling  those  which  elsewhere 

!  form  the  boundaries  of  the  cancelli ;  these  consist  of  but  one  layer  of 

,  bony  matter,  and  show  none  of  the  varieties  previously  adverted  to ;  they 
are  not  penetrated  by  vessels,  but  are  nourished  only  by  their  surfaces ; 
and  they  consequently  exhibit  to  us  the  elements  of  the  osseous  struc- 
ture in  their  simplest  form.     It  will  be  desirable,  therefore,  to  commence 

;  with  the  description  of  these. 

j  290.  When  a  thin  natural  lamella  of  this  kind  is  examined,  it  is  found 
to  be  chiefly  made  up  of  a  substance  which  is  nearly  homogeneous, 

'  sometimes  exhibiting  indistinct  traces  of  a  fibrous  arrangement ;  this, 
however,  may  be  generally  resolved  by  prolonged  boiling,  into  an  assem- 

•  blage  of  minute  granules,  varying  in  size  from  l-6000th  to  l-14,000th 

Fig.  46. 


Extremity  of  Os  femo- 
ris,  showing,  cancellateil 
structure :— a,  thin  layer 
of  bone,  in  contact  with 
the  articular  cartilage ; 
b,  cancelli. 


Lacunje  of  Osseous  substance,  magnified  500  diameters :— a,  central  cavity;  6,  its  ramifications. 

of  an  inch,  which  are  more  or  less  angular  in  shape,  and  seem  to  cohere 
by  the  medium  of  some  second  substance,  which  is  dissolved  by  the 
boiling.  They  are  composed  of  Calcareous  salts,  apparently  in  chemical 
union  with  the  Gelatine  that  forms  the  basis  of  the  osseous  substance. 
In  the  midst  of  this  granular  substance,  a  number  of  dark  spots  are  to 
be  observed,  the  form  of  which  is  very  peculiar.  In  their  general  out- 
line, they  are  usually  somewhat  oval ;  but  they  send  forth  numerous 
radiating  prolongations  of  extreme  minuteness,  which  may  be  frequently 


174 


STRUCTURE  AND   ENDOWMENTS   OF   ANIMAL  TISSUES. 


traced  to  a  considerable  distance.  These  spots,  known  as  the  osseous 
corpuscles  (sometimes  termed  the  Purkinjean  corpuscles^  after  the  name 
of  their  discoverer),  are  highly  characteristic  of  the  true  bony  structure, 
being  never  deficient  in  the  minutest  parts  of  the  bones  of  the  higher 
animals,  although  those  of  Fishes  are  frequently  destitute  of  them. 
These  corpuscles  were  formerly  supposed,  from  their  dark  appearance, 
to  be  opaque,  and  to  consist  of  aggregations  of  calcareous  matter  which 
would  not  transmit  the  light :  but  it  is  now  quite  certain,  that  they  are 
lacunce  or  open  spaces ;  and  that  the  radiating  prolongations  from  them, 
which  are  far  smaller  than  the  minutest  capillary  vessel,  are  canaliculi, 
or  delicate  tubes.  Of  these  canaliculi,  some  may  be  seen  to  interlace 
freely  with  each  other,  whilst  others  proceed  towards  the  surface  of  the 
bony  lamella ;  and  thus  a  system  of  passages,  not  by  any  means  wide 
enough  to  admit  the  blood-corpuscles,  but  capable  of  transmitting  the 
fluid  elements  of  the  blood,  or  matters  selected  from  them,  is  established 
through  the  whole  substance  of  the  lamella. 

291.  The  lacunae  of  Human  bone  have  an  average  length  of  l-1800th 
of  an  inch ;  and  they  are  usually  about  half  as  wide,  and  one-third  as 
thick.  The  diameter  of  the  canaliculi  is  from  l-12,000th  to  l-20,000th 
of  an  inch.  Their  size  and  form  differ  greatly,  however,  in  the  different 
classes  of  Vertebrata ;  so  that  it  is  usually  possible  to  refer  a  mere  frag- 
ment of  bone  to  its  proper  group,  by  an  examination  of  its  minute 
structure.  The  succeeding  figure  represents  the  arrangement  of  these 
lacunae  and  canaliculi  in  the  bony  scale  of  a  fish  (the  Lepidosteus) ; 
which  is  almost  the  only  existing  representative  of  a  large  class  of  bony- 
scaled  Fishes,  that  formerly  tenanted  the  seas.  Its  lacunae  will  be 
seen  to  differ  greatly  in  form  from  those  of  human  bone ;  and  the 
canaliculi  which  proceed  from  them  are  much  fewer  in  number. — The 
purpose  of  this  penetration  of  the  osseous  texture  by  such  a  complicated 
apparatus  of  tubuli,  can  scarcely  be  anything  else  than  the  maintenance 

Fig.  47. 


Section  of  the  bony  scale  of  Lepidosteus ;— a,  showing  the  regular  distribution  of  the  lacunaB  and  of 
the  connecting  canaliculi;  b,  small  portion  more  highly  magnified. 

of  its  vitality  by  the  continual  percolation  of  nutrient  fluid,  drawn  into 
the  system  of  lacunae  and  canaliculi  from  the  neighbouring  blood-vessels. 
Thus  the  nutrition  of  the  ultimate  osseous  texture,  though  carried  on 
upon  the  same  general  plan  with  that  of  Cartilage,  differs  in  this : — 
that  there  is  a  provision  in  Bone  for  the  ready  transmission  of  nutrient 
matter  through  its  texture,  by  means  of  minute  channels,  which  does 
not  exist  in  Cartilage ;  a  difference  obviously  required  by  the  greater 
solidity  of  the  substance  of  the  former,  which  does  not  allow  of  the 
diffused  imbibition,  that  is  permitted  by  the  softer  and  moister  nature 
of  the  latter.     We  shall  presently  find  that  these  channels  are  only 


I 


STRUCTURE   OF   BONE. 


175 


formed  at  a  late  stage  of  the  development  of  bone,  where  the  remaining 
tissue  has  acquired  its  completest  consolidation. 

292.  Now,  as  already  remarked,  the  simple  structure  just  described 
is  found,  not  merely  in  the  delicate  plates  which  form  the  thinnest  part 
of  certain  bones  in  Man,  but  also  in  those  lamellae,  which  form  the  walls 
of  the  cancelli  of  the  larger  and  thicker  bones.  Every  one  of  these 
lamellae  repeats,  in  fact,  the  same  history.  The  cancelli  are  lined  by  a 
membrane  derived  from  that  of  the  cavity  of  the  shaft,  over  which 
blood-vessels  are  minutely  distributed ;  between  these  blood-vessels  and 
the  osseous  texture  is  a  layer  of  cells ;  and  from  the  materials  selected 
and  communicated  by  these,  each  lamella  is  nourished,  through  its 
system  of  radiating  canaliculi  and  nutritive  centres.  The  cancelli,  at 
the  time  of  their  formation  in  the  foetal  bone,  are  entirely  filled  with 
such  cells ;  which  appear  (as  will  be  presently  explained)  to  be  the 
descendants  of  the  cells  of  the  original  cartilage ;  but  in  the  adult 
bone,  a  large  proportion  of  them  are  filled  with  fatty  matter,  which 
they  secrete  into  their  cavities. — The  vessels  of  the  cancellated  struc- 
ture at  the  extremities  of  the  long  bones  are  derived  from  those  of  the 
medullary  cavity,  which  is  penetrated  by  large  trunks  from  the  exterior  ; 
and  in  the  flat  bones,  they  form  a  system  of  their  own,  connected  with 
the  vessels  of  the  exterior  by  several  smaller  trunks. 

293.  The  solid  osseous  texture  which  forms  the  cylindrical  shafts  of 
the  long  bones,  and  the  thick  external  plates  of  the  denser  flat  bones, 
is  not  cut  ofi"  from  nutritive  action  in  the  degree  in  which  it  might  seem 
to  be ;  for  it  is  penetrated  by  a  series  of  large  canals,  termed  the 
Haversian  (after  Clopton  Havers,  their  discoverer),  which  form  a  net- 
work in  its  interior,  and  which  serve  for  the  transmission  of  blood- 
vessels through  its  substance  (Fig.  48).  These  canals,  in  the  long  bones, 
run  for  the  most  part  in  a  direction  parallel  to 
the  central  cavity ;  and  they  communicate  with 
this,  with  the  external  surface,  with  the  cancelli, 
and  with  each  other,  by  frequent  transverse 
branches;  so  that  the  whole  system  forms  an 
irregular  network,  pervading  every  part  of  the 
solid  texture,  and  adapted  for  the  establishment 
of  vascular  communications  throughout.  The 
diameter  of  the  Haversian  canals  varies  from 
l-2500th  to  l-200th  of  an  inch,  or  more ;  their 
average  diameter  may  be  stated  at  about  l-500th 
of  an  inch.  They  are  lined  by  a  membrane 
which  is  continuous  with  that  of  the  external 
surface,  and  which  carries  this  inwards,  so  to 
speak,  to  form  the  lining  membrane  of  the  cen- 
tral cavity,  and  of  the  cancelli ; — and  the  cavity 
of  the  tube  encloses  a  single  twig  of  an  artery 
or  vein.  Thus  we  may  consider  the  whole 
Osseous  texture  as  enclosed  in  a  membranous 

bag;  on  which  blood-vessels  are  minutely  dis-  ^"Su^ol thTSlS o^l^<^'^^ih^^ 
tributed,  and  which  is  so  carried  into  the  bone  ^"^^1^^,  "s^'diiatauroi 
by  involutions  and  prolongations,  that  no  part  another  venous  canai. 
of  the  latter  is  ever  far  removed  from  a  vascular  surface. 


Havorsir.n  Canal,  seen  on  a  lon- 
gitudinal section  of  the  compact 


176  STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

294.  In  the  adult  bone,  the  cells  which  fill  the  remaining  cavity  of 
these  canals  secrete  fatty  matter.  This  is  particularly  evident  in  the 
case  of  the  central  cavity,  which  may  be  considered  as  an  immensely 
dilated  Haversian  canal,  where  they  constitute  the  medulla  or  marrow. 
It  does  not  appear  that  these  take  any  active  part  in  the  nutrition  of 
the  bone ;  indeed,  in  the  bones  of  Birds  the  shaft  is  entirely  hollow, 
and  air  is  admitted  into  it  from  the  lungs,  so  that  its  lining  membrane 
is  rendered  subservient  to  the  aeration  of  the  blood. 

295.  The  arrangement  of  the  elementary  parts  of  the  osseous  sub- 
stance around  the  Haversian  canals  is  very  interesting  and  beautiful. 
When  a  transverse  section  of  a  long  bone  is  made,  the  open  orifices  of 
the  longitudinal  canals  present  themselves  at  intervals,  sometimes  con- 
nected by  a  transverse  canal  where  the  section  happens  to  traverse  this. 
Around  these  orifices,  we  see  the  osseous  matter  arranged  in  the  form 
of  cylinders,  which  appear  to  be  marked  by  concentric  circles  (Fig.  49, 
1,  2).  Now  when  one  of  these  circles  is  minutely  examined,  it.  is  found 
to  be  made  up  of  a  series  of  lacunae,  analogous  to  those  already 
described ;  these,  however,  are  seldom  or  never  so  continuous  as  to  form 
a  complete  circle.     The  long  sides  of  the  lacunae  are  directed,  the  one 

Fig.  49. 


Minute  structure  of  bone,  drawn  with  the  microscope  from  nature.  Magnified  300  diameters.  1.  One  of 
the  Haversian  canals  surrounded  by  its  concentric  lamellae.  The  lacuna  are  seen  between  the  lamellae; 
but  the  radiating  tubuli  are  omitted.  2.  An  Haversian  canal  with  its  concentric  laminae,  lacuna?,  and 
radiating  tubuli.  3.  The  area  of  one  of  the  canals.  4,  4.  Direction  of  the  lamellae  of  the  great  medullary 
canal.  Between  the  lamellae  at  the  upper  part  of  the  figure,  several  very  long  lacunae  with  their  tubuli  are 
seen.  In  the  lower  part  of  the  figure  the  outlines  of  three  other  canals  are  given,  in  order  to  show  their 
form  and  mode  of  arrangement  in  the  entire  bone. 

towards  the  Haversian  canal  (3)  in  the  centre,  the  other  towards  the 
circular  row  next  beyond  it.  And  when  the  course  of  the  canaliculi  is 
traced,  it  is  found  that  these  converge  on  the  inner  side  towards  the 
central  canal,  inosculating  with  those  of  the  series  next  within,  whilst 
those  of  the  outer  side  pass  outwards  in  a  radiating  or  diverging  direc- 
tion, to  inosculate  with  those  of  the  series  next  external.  Thus  a  com- 
plete communication  is  formed,  by  means  of  this  system  of  radiating 
canaliculi  and  intervening  lacunae,  between  the  central  canal  and  the 


I 


COMPOSITION   OF   BONE.  177 

outermost  cylindrical  lamella  of  bony  matter ;  and  each  of  these  lamellae 
derives  its  nourishment  from  the  vessels  of  the  central  canai,  through 
the  lamellae  which  intervene  between  itself  and  the  vascular  membrane 
lining  that  tube. 

296.  Thus  every  one  of  the  Haversian  canals  is  the  centre  of  a 
cylindrical  ossicle,  which  is  complete  in  itself,  as  far  as  its  elementary 
structure  is  concerned,  and  which  has  no  dependence  on,  or  connexion 
with,  other  similar  ossicles.  These  are  arranged,  however,  side  by  side, 
like  sticks  in  a  faggot ;  they  are  bound  together  by  a  thin  cylinder  of 
bone,  on  the  exterior  of  all,  which  derives  its  nourishment  from  the 
periosteum,  or  enveloping  membrane :  in  like  manner,  the  hollow  bundle 
is  lined  by  a  similar  cylinder,  which  surrounds  the  great  medullary 
cavity,  and  is  nourished  by  its  vascular  membranes;  and  the  spaces 
that  here  and  there  intervene  between  the  ossicles  are  filled  up  with 
laminae,  which  are  parallel  to  those  of  the  external  and  internal  cylinders, 
and  which  seem  to  derive  their  nutriment  from  them  (Fig.  49,  4).  In 
this  manner,  the  whole  structure  acquires  great  density  and  solidity. — 
The  structure  of  the  outer  and  inner  tables  of  the  skull,  and  of  other 
thick  solid  layers  of  bone,  is  precisely  similar ;  except  that  the  Haver- 
sian canals  have  no  such  definite  directions,  and  form  an  irregular  net- 
work. 

297.  Thus  we  see  that  each  of  the  lamellse  of  bone  surrounding  an 
Haversian  canal,  or  bounding  the  cancelli,  may  be  regarded  as  a  repe- 
tition of  the  simple  bony  plate,  which  draws  its  nourishment  direct  from 
the  vascular  membrane  covering  its  surface,  by  means  of  its  system  of 
lacunae  and  canaliculi.  The  membrane  lining  the  Haversian  canals, 
cancelli,  and  central  medullary  cavity,  is  an  internal  prolongation  of 
that  which  clothes  the  exterior ;— just  as  the  mucous  membranes,  with 
their  extensions  into  glandular  structures,  are  internal  prolongations  of 
the  true  skin.  Every  Haversian  canal  and  every  cancellus  are  repe- 
titions of  each  other  in  all  essential  particulars,  their  form  alone  being 
different.  The  central  medullary  canal  is  but  an  enlarged  Haversian 
canal  or  cancellus.  And  the  whole  cylindrical  shaft  is  a  collection  of 
ossicles,  each  of  which  is  a  miniature  representation  of  itself,  being  a 
hollow  cylinder,  with  a  central  vascular  cavity. 

298.  The  principal  features  of  the  Chemical  constitution  of  Bone  are 
easily  made  evident.  After  all  the  accessory  parts  have  been  removed, 
and  nothing  remains  but  the  real  osseous  texture,  tjiis  may  be  separated, 
by  simple  processes,  into  its  two  grand  constituents, — the  animal  basis, 
and  the  calcareous  matter.  The  latter  may  be  entirely  removed  by 
maceration  of  the  bone  in  dilute  Muriatic  or  Nitric  acid ;  and  a  substance 
of  cartilaginous  appearance  is  then  left,  which,  when  submitted  to  the 
action  of  boiling  water  for  a  short  time,  is  almost  entirely  dissolved 
away,  and  the  solution  forms  a  dense  jelly  on  cooling.  The  same  sub- 
stance. Gelatine,  may  be  obtained  by  long  boiling  under  pressure,  from 
previously  unaltered  bone ;  and  the  calcareous  matter  is  then  left  in  a 
friable  condition.  By  submitting  a  bone  to  a  heat  sufficient  to  decom- 
pose the  animal  matter,  without  dissipating  any  of  the  earthy  particles, 
we  may  obtain  the  whole  calcareous  matter  in  situ;  but  the  slightest 

iolence  is  sufficient  to  disintegrate  it.     The  bones  of  persons  long 

12 


1T8  STRUCTURE   AND  ENDOWMENTS   OF  ANIMAL   TISSUES. 

buried  are  often  found  in  this  condition  ;  their  form  and  position  being 
retained  until  they  are  exposed  to  the  air,  or  are  a  little  shaken,  when 
they  crumble  to  dust.  The  proportion  of  the  earthy  matter  of  Bones 
to  the  animal  basis  may  be  differently  stated,  according  as  we  include, 
in  our  estimate  of  the  latter,  the  contents  of  the  medullary  cavity,  the 
Haversian  canals,  and  the  cancelli,  or  confine  ourselves  to  that  portion 
only  of  the  animal  matter  which  is  united  with  the  calcareous  element 
in  the  proper  osseous  tissue.  According  to  the  recent  experiments  of 
Dr.  Stark,*  the  relative  amount  of  the  two  elements,  in  the  latter 
estimate,  is  subject  to  very  little  variation,  either  in  the  different  classes 
of  animals,  or  in  the  same  species  at  different  ages,  the  animal  matter 
composing  about  one-third,  or  33J  per  cent.,  and  the  mineral  matter 
two-thirds,  or  66f  per  cent.  The  degree  of  hardness  of  bone  does  not 
altogether  depend,  therefore,  on  the  amount  of  earthy  matter  they  may 
contain ;  for  the  flexible,  semi-transparent,  easily-divided  bones  of  Fish 
contain  as  large  an  amount  of  animal  matter,  as  the  ivory-like  leg-bones 
of  the  Deer  or  Sheep.  The  usual  analyses  of  Bone,  however,  have 
been  made  upon  the  former  kind  of  estimate :  and  they  show  that  the 
proportion  of  the  earthy  matter  to  the  whole  of  the  animal  substance 
contained  in  bone  varies  much  in  different  animals,  in  the  same  animal 
in  different  ages,  and  even  in  different  parts  of  the  same  skeleton.  The 
reason  of  this  will  be  apparent,  when  the  history  of  the  growth  of  Bone 
has  been  explained ;  since  there  is  a  gradual  filling-up  of  all  the  cavities 
at  first  occupied  by  fat-cells,  vessels,  &c.,  which  does  not  cease  with 
adult  age,  but  which  continues  during  the  whole  of  life.  In  this  manner 
the  bones  of  old  persons  acquire  a  high  degree  of  solidity,  but  they 
become  brittle  in  proportion  to  their  hardness.  From  the  same  cause, 
the  more  solid  bones  contain  a  larger  proportion  of  bone-earth  than 
those  of  a  spongy  or  cancellated  texture ;  the  temporal  bone,  for  exam- 
ple, containing  63i  per  cent.,  whilst  the  scapula  possesses  only  54  per 
cent.  In  the  former  of  these  bones,  the  proportion  is  nearly  the  same 
as  that  which  exists  in  pure  osseous  tissue,  the  amount  of  the  remaining 
tissues  which  it  includes  being  very  small,  on  account  of  the  solidity  of 
the  bone ;  but  the  latter  contains  in  its  cancelli  a  large  quantity  of 
blood-vessels,  fat-cells,  &c.,  which  swell  the  proportion  of  the  animal 
matter  from  33J  to  46  per  cent. 

299.  The  Lime  of  bones  is  for  the  most  part  in  a  state  of  Phosphate, 
especially  among  the  higher  animals ;  the  remainder  is  a  Carbonate. 
In  Human  bones,  the  proportion  of  the  latter  seems  to  be  about  one- 
sixth  or.  one-seventh  of  the  whole  amount  of  bone-earth.  In  the  bones 
of  the  lower  animals,  however,  the  proportion  of  Carbonate  is  greater ; 
and  it  is  curious  that  in  callus,  exostosis,  and  other  irregular  osseous 
formations  in  the  higher  animals,  the  proportion  of  the  Carbonate 
should  be  much  greater  than  in  the  sound  bone.  In  caries,  however, 
the  proportion  of  the  Carbonate  is  less  than  usual.  The  composition 
of  the  Phosphate  of  Lime  in  Bones,  is  somewhat  peculiar ;  eight  pro- 
portions of  the  base  being  united  with  three  of  the  acid.  According  to 
Professor  Graham,  it  is  to  be  regarded  as  a  compound  of  two  tribasic 

*  Edinburgh  Medical  and  Surgical  Journal,  April,  1845. 


I 


I 


COMPOSITION   OF   BONE.  179 

pnDSphates ;  one  atom  of  the  neutral  phosphate  (in  which  one  propor- 
tional of  the  ucid  is  united  with  two  of  lime  and  one  of  water),  being 
united  with  two  proportionals  of  the  alkaline  phosphate  (in  which  one 
part  of  acid  is  united  with  three  of  the  base),  together  with  an  atom  of 
water,  which  is  driven  off  by  calcination.  Besides  these  components, 
some  Chemists  assert  that  a  small  quantity  of  Fluoride  of  calcium  is 
present  in  Bone ;  but  this  is  rather  doubtful,  since  it  has  been  shown 
by  Dr.  G.  0.  Rees  that  the  solvent  action  upon  glass,  which  has  been 
supposed  to  be  characteristic  of  fluoric  acid,  may  be  imitated  by  phos- 
phoric acid  in  combination  with  water,  which,  if  heated  upon  glass  of 
inferior  quality  until  it  volatilizes,  will  act  upon  it  with  considerable 
energy. — Other  saline  matters,  such  as  phosphate  of  magnesia,  oxides 
of  iron  and  manganese,  and  chloride  of  sodium,  are  found  in  bones  in 
small  amount. 

300.  The  first  development  of  Bone  is  usually  preceded  by  the  for- 
mation of  a  Cartilaginous  structure,  which  occupies  the  place  after- 
wards-to  be  taken<by  the  bone;  and  it  is  commonly  considered  that  the 
bone  is  formed  by  the  calcification  of  the  cartilage-substance.  This, 
however,  does  not  appear  to  be  the  case,  as  will  be  presently  shown ; 
and  it  would  probably  be  more  correct  to  say  that  the  cartilage  is  super- 
seded by  bone.  Moreover,  Bone  is  frequently  developed  in  the  sub- 
stance of  Fibrous  membranes  ;  and  the  structure  produced  by  this  intra- 
memhranous  ossification  cannot  be  distinguished  from  that  which  is 
generated  by  the  intra-cartilaginous. — We  shall  commence  the  history 
of  the  development  of  Bone,  with  the  period  in  which  its  condition 
resembles  that  of  the  permanent  Cartilages.  As  already  mentioned, 
there  is  no  essential  difference  between  the  temporary  and  permanent 
Cartilages,  in  regard  to  their  ultimate  structure ;  the  former,  however, 
are  more  commonly  traversed  by  vessels,  especially  when  their  mass  is 
considerable.  These  vessels,  however,  do  not  pass  at  once  from  the 
exterior  of  the  cartilage  into  its  substance ;  but  they  are  conveyed  in- 
wards along  canals,  which  are  lined  by  an  extension  of  the  perichondrium 
or  investing  membrane,  and  which  may  thus  be  regarded  as  so  many 
involutions  of  the  outer  surface  of  the  cartilage.  These  canals  are  espe- 
cially developed  at  certain  points,  which  are  to  be  the  centres  of  the 
ossifying  process;  of  these  puncta  ossifieationis,  we  usually  find  one  in 
the  centre  of  the  shaft  of  a  long  bone,  and  one  in  each  of  its  epiphyses  ; 
in  the  flat  bones  there  is  one  in  the  middle  of  the  surface,  and  one  in 
each  of  the  principal  processes.  Up  to  a  late  ;stage  of  the  ossifying 
process,  the  parts  which  contain  distinct  centres  are  not  connected  by 
bony  union,  so  that  they  fall  apart  by  maceration;  and  even  when  they 
should  normally  unite,  they  sometimes  remain  separate, — as  in  the  case 
of  the  Frontal  bone,  in  which  we  frequently  meet  with  a  continuation 
of  the  sagittal-suture  down  the  middle,  dividing  it  into  two  equal  halves, 
which  have  originated  in  two  distinct  centres  of  ossification.  It  is  inte- 
resting to  remark  that,  in  the  two  lowest  classes  of  Vertebrata,— Fishes 
and  Reptiles,— we  find  the  several  parts  of  the  osseous  system  present- 
ing, in  a  permanent  form,  many  of  the  conditions  which  are  transitory 
in  the  higher ;  thus  the  different  portions  of  each  vertebra,  the  body, 
lateral  arches,  spinous  and  transverse  processes,  &c.,  which  have  then- 


180 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 


distinct  centres  of  ossification,  but  which  early  unite  in  Man,  remain 
permanently  distinct  in  the  lower  Fishes ;  the  division  of  the  frontal 
bone,  just  adverted  to,  is  constant  amongst  Fishes  and  Reptiles ;  and  in 
these  classes  we  meet  with  a  permanent  separation  of  the  parts  of  the 
occipital  and  temporal  bones,  which,  being  formed  from  distinct  centres 
of  ossification,  are  at  first  distinct  in  the  higher  animals.  ^ 

301.  During  the  formation  of  the  punctum  ossificatioms,  and  the 
spread  of  the  vessels  into  the  cartilaginous  matrix,  certain  changes  are 
taking  place  in  the  substance  of  the  latter,  preparatory  to  its  conversion 
into  bone.  Instead  of  single  isolated  cells,  or  groups  of  two,  three,  or 
four,  such  as  we  have  seen  to  be  characteristic  of  ordinary  Cartilage 
(§  267),  we  find,  as  we  approach  the  ossifying  centre,  clusters  made  up 
of  a  larger  number,  which  appear  to  be  formed  by  a  continuance  of  the 
same  multiplying  process  as  that  already  described  (Fig.  50).     And 


^P     09   i 


Fig.  60. 


ft!^  % 


sl^te 


m 


m 


OD^   (^ 


Section  of  Cartilage,  near  the  seat  of  ossification ;  each  single  cell  haying  given  birth  to  four,  five,  or  six 
cells,  which  form  clusters.  These  clusters  become  larger  towards  the  right  of  the  figure,  and  their  cells 
more  numerous  and  larger ;  their  long  diameter  being  l-1500th  of  an  inch. 

when  we  pass  still  nearer,  we  see  that  these  clusters  are  composed  of  a 
yet  greater  number  of  cells,  which  are  arranged  in  long  rows,  whose 
direction  corresponds  with  the  longitudinal  axis  of  the  bone ;  these  clus- 
ters are  still  separated  by  intercellular  substance,  and  it  is  in  this,  that 
the  ossific  matter  is  first  deposited  (Fig.  51).     Thus  if  we  separate  the 

Fig.  61. 


The  same  cartilage  at  the  seat  of  ossification:  the  clusters  of  cells  are  arranged  in  columns;  the  intercel- 
lular spaces  between  the  columns  being  l-3250th  of  an  inch  in  breadth.  To  the  right  of  the  figure,  osseous 
fibres  are  seen  occupying  the  intercellular  spaces,  at  first  bounding  the  clusters  laterally,  then  splitting 
them  longitudinally  and  encircling  each  separate  cell.  The  greater  opacity  of  the  right  hand  border  is  due 
to  a  threefold  cause,  the  mcrease  of  osseous  fibres,  the  opacity  of  the  contents  of  the  cells,  and  the  multipli- 
cation of  oil-globules. 

cartilaginous  and  the  osseous  substance  at  this  period,  we  find  that  the 
ends  of  the  rows  of  cartilage-cells  are  received  into  deep  narrow  cups  of 


CONVERSION  OF  CARTILAGE  INTO  BONE.  181 

e,  formed  by  the  transformation  of  the  intercellular  substance  be- 
tween them.  Immediately  upon  the  ossifying  surface,  the  nuclei,  which 
were  before  closely  compressed,  separate  considerably  from  one  another, 
by  the  increase  of  material  within  the  cells ;  and  the  nuclei  themselves 
become  larger  and  more  transparent.  These  changes  constitute  the  first 
stage  of  the  process  of  ossification,  which  extends  only  to  the  calcifica- 
tion of  the  intercellular  substance ;  in  this  stage  there  are  no  blood- 
vessels directly  concerned.  The  bony  lamellae  thus  formed,  mark  out 
the  boundaries  of  the  cancelli  and  Haversian  canals,  which  are  after- 
wards to  occupy  a  part  of  the  space  that  is  hitherto  filled  by  the  rows 
of  cartilage  corpuscles. 

302.  Up  to  this  point,  there  is  no  essential  difference  in  the  accounts 
of  those  who  have  most  carefully  studied  the  process  of  ossification ;  but 
in  regard  to  the  history  of  its  subsequent  stages,  there  is  much  discre- 
pancy ;  and  this  especially  with  respect  to  the  origin  of  the  bone-lacunae, 
which  some  regard  as  metamorphosed  cartilage-cells,  others  as  the  spaces 
originally  occupied  by  their  nuclei,  whilst  others  do  not  regard  them  as 
in  any  way  derived  from  the  cartilage-cells,  but  consider  them  as  a  new 
formation.  Much  may  doubtless  be  urged  in  favour  of  each  view ;  the 
author's  own  observations  incline  him  to  the  latter,  and  lead  him  to 
regard  the  lacunae  as  cells,  which,  like  the  pigment-cells  of  Batrachia, 
&c.,  have  sent  out  the  stellate  prolongations  that  constitute  the  canali- 
culi.  All  stages  of  gradation  may  be  traced,  between  simple  rounded 
cavities, — whose  correspondence  in  size  with  the  cells  that  are  scattered 
in  the  midst  of  the  consolidating  blastema  leaves  scarcely  any  doubt  of 
their  identity  with  these, — and  the  lenticular  lacuna  with  numbers  of 
canaliculi  proceeding  from  it.  These  gradations  are  particularly  well 
seen  during  the  process  of  ossification ;  so  that  it  seems  probable  that 
the  radiating  extension  of  the  cells  takes  place  during  the  consolidation 
of  the'  surrounding  tissue. — It  is  an  additional  argument  against  the 
idea  that  the  bone-lacunae  in  any  way  originate  from  the  cartilage-cells, 
that  they  are  found  to  present  exactly  the  same  characters  in  bone 
which  is  developed  in  the  substance  of  fibrous  membrane  (after  the 
manner  to  be  presently  described),  and  in  the  formation  of  which,  there- 
fore, cartilage  has  had  no  participation. 

303.  Although,  in  a  large  proportion  of  the  skeleton,  the  formation 
of  Bone  is  thus  preceded  by  that  of  cartilage,  yet  such  is  by  no  means 
invariably  or  necessarily  the  case ;  for  the  flat  bones,  such  as  the  scapula, 
and  those  forming  the  roof  of  the  skull,  have  usually  only  a  centre  of 
cartilage,  beyond  which  the  ossifying  process  extends  in  membrane 
only.  This  membrane  is  chiefly  composed  of  fibrous  fasciculi,  corre- 
sponding with  those  of  the  white  fibrous  tissues ;  but  amongst  these  are 
seen  numerous  cells,  some  about  the  size  of  blood-discs,  but  others  two 
or  three  times  larger,  containing  granular  matter ;  and  a  soft  amorphous 
or  faintly  granular  matter  is  also  found  interposed  amidst  the  fibres  and 
cells.  The  process  of  ossification  here  seems  essentially  to  consist  in 
the  consolidation  of  the  fibres  by  earthy  matter;  for  the  first  bony 
deposit  is  seen  as  an  irregular  reticulation,  very  loose  and  open  towards 
its  edges,  and  there  frequently  presenting  itself  in  the  form  of  distinct 
spicula,  which  are  continuous  with  fasciculi  of  fibres  in  the  surroundmg 


182  STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

membrane.  The  limits  of  the  calcifying  deposit  may  be  traced  by  the 
opaque  and  granular  character  of  the  parts  affected  by  it;  and  it  gradu- 
ally extends  itself,  involving  more  and  more  of  the  surrounding  mem- 
brane, until  the  foundation  is  laid  for  the  entire  bone.  Everywhere  the 
part  most  recently  formed  consists  of  a  very  open  reticulation  of  fibro- 
calcareous  spicula,  whilst  the  older  part  is  rendered  harder  and  more 
compact  by  the  increase  in  the  number  of  these  spicula.  As  the  process 
advances,  and  the  plate  of  bone  thickens,  a  series  of  grooves  or  furrows, 
radiating  from  the  ossifying  centre,  are  found  upon  its  surface;  and 
these,  by  a  further  increase  in  thickness,  occasioned  by  a  deposit  of 
ossific  matter  all  around  them,  are  gradually  converted  into  close  canals 
(the  Haversian),  which  contain  blood-vessels,  and  are  lined  by  processes 
of  the  investing  membrane.  The  lacunae  and  canaliculi  seem  to  take 
their  origin  in  the  cells  which  are  interspersed  among  the  fibres,  their 
prolongations  extending  themselves,  and  insinuating  themselves  through 
the  spaces  left  between  the  interlacing  fibres,  whilst  the  process  of  cal- 
cification is  going  on. 

304.  The  first  osseous  tissue  which  is  formed  by  either  of  these  pro- 
cesses, has  an  irregular  cancellated  structure,  analogous  to  that  which 
is  found  at  the  extremities  of  the  long  bones  in  adults.  This  is  gradu- 
ally modified  by  changes  which  essentially  consist  in  absorption  and 
new  deposition ;  for  the  absorptive  process  first  unites  minute  areolae 
into  larger  ones,  by  removing  their  partitions  ;  and  it  is  upon  their  in- 
terior w^alls  that  new  osseOus  lamellae  are  now  deposited,  from  materials 
supplied  by  the  blastema  they  contain.  It  is  by  a  process  of  this  kind, 
that  the  central  medullary  cavity  is  first  formed  in  the  bones  of  young 
animals.  At  an  early  period,  no  such  cavity  exists,  and  its  place  is 
occupied  by  small  cancelli;  this  is  the  permanent  condition  of  the  bones 
in  most  Reptiles.  The  cancelli  gradually  enlarge,  however ;  and  those 
within  the  shaft  coalesce  with  one  another  until  a  continuous  tube  is 
formed,  around  which  the  cancelli  are  large,  open,  and  irregular.  At 
the  same  time,  the  diameter  of  the  surrounding  shaft  is  increasing  by 
the  process  of  interstitial  growth  just  described;  so  that  the  size  of  the 
medullary  cavity  at  last  becomes  greater  than  that  of  the  whole  shaft 
when  its  formation  commenced.  The  aggregation  of  the  osseous  matter 
in  a  hollow  cylinder,  instead  of  a  solid  one,  is  the  form  most  favourable 
to  strength,  as  may  be  easily  proved  upon  mechanical  principles.  The 
same  arrangement  is  adopted  in  the  arts,  wherever  it  is  desired  to  obtain 
the  greatest  strength  with  a  limited  amount  of  material. 

305.  The  growth  of  Bones  takes  place  by  the  addition  of  new  tissue 
to  the  part  already  formed ;  but  this  addition  may  take  place  in  three 
modes,— namely,  by  the  development  of  new  bone  in  the  cartilage  yet 
remaining  between  the  different  centres  of  ossification ;  by  the  develop- 
ment of  new  bone  in  the  membrane  covering  the  surface;  and  by  the 
interstitial  formation  of  new  layers  within  the  Haversian  canals  and 
cancelli  of  the  part  already  formed,  by  which  the  requisite  solidity  is 
given  to  it.  Of  the  first  process  we  have  the  most  characteristic  ex- 
ample in  the  increase  in  length  of  a  long  bone,  by  the  ossification  of 
the  cartilage  which  intervenes  between  the  shaft  and  the  epiphyses, 
and  which  continues  to  grow,  up  to  the  time  of  the  final  union  of  these 


■ 


REGENERATION   OF   BONE.  183 


parts.  Thus  it  was  long  since  proved  by  the  experiments  of  Hales  and 
Hunter,  that  the  growth  of  a  long  bone  takes  place  chiefly  towards  the 
extremities ;  for  they  found  that,  when  metallic  substances  were  inserted 
in  the  shaft  of  a  growing  bone  of  a  young  animal,  the  distance  between 
them  was  but  little  altered  after  a  long  interval,  whilst  the  space  be- 
tween the  extremities  of  the  bone  had  greatly  increased.  And  it  seems 
that,  at  a  later  period,  when  the  epiphyses  have  become  completely 
united  to  the  shaft,  an  elongation  continues  to  take  place,  by  the  slow 
ossification  of  the  articular  cartilage. — Again,  the  bone  is  progressively 
increased  in  thickness,  by  the  gradual  production  of  new  osseous  matter 
upon  its  surface ;  this  production  being  effected  by  the  conversion  of 
the  inner  layer  of  the  periosteum,  the  fibres  of  which  are  found  to  be 
continuous  with  those  of  the  animal  matrix  of  the  surface  of  the  bone. — 
And  it  is  by  the  successive  formation  of  new  layers  of  osseous  tissue, 
one  within  another,  giving  the  appearance  of  concentric  rings  when  the 
Haversian  canals  are  cut  across  (Fig.  49),  that  the  proportion  of  hard 
to  soft  parts  in  bone  is  gradually  increased ;  the  calibre  of  the  Haver- 
sian canals  being  correspondingly  diminished.  Of  this  we  have  a 
curious  exemplification  in  the  antlers  of  the  deer,  in  which  the  cavity 
of  the  canals  is  gradually  choked  up  by  the  formation  of  osseous 
tissue,  until  the  vascular  supply  is  cut  off,  and  the  death  of  the  bone  is 
the  result. 

306.  The  difference  in  the  relations  of  the  Osseous  substance  to  the 
l^fc  vascular  network,  at  different  ages, — accounting  for  the  variations  in  the 
■™^  rapidity  of  its  nutrition  and  reparation, — is  well  displayed  in  the  effects 

of  Madder.  This  substance  has  a  peculiar  afiinity  for  Phosphate  of 
Lime ;  so  that  when  the  latter  is  formed  by  precipitation  in  a  fluid 
tinged  with  madder,  it  attracts  colour  to  it  in  its  descent,  and  falls  to 
the  bottom  richly  tinted.  Now  when  animals  are  fed  with  this  sub- 
stance, it  is  found  that  their  bones  become  tinged  with  it,  the  period 
required  being  in  the  inverse  proportion  to  their  age.  Thus  in  very 
young  animals  a  single  day  sufiices  to  colour  the  entire  skeleton,  for  in 
them  there  is  no  osseous  matter  far  from  the  vascular  surfaces ;  when 
sections  are  made,  however,  of  the  bones  thus  tinged,  it  is  found  that 
the  colour  is  confined  to  the  immediate  neighbourhood  of  the  Haversian 
canals,  each  of  which  is  encircled  by  a  crimson  ring.  In  full-grown 
animals,  the  bones  are  very  slowly  tinged ;  because  the  osseous  texture 
is  much  more  consolidated  and  less  permeable  to  fluid  than  in  earlier 
life ;  and  because  the  vascular  membrane  lining  the  Haversian  canals 
is  removed  further  from  the  outer  and  older  layers  of  osseous  tissue 
which  surround  them,  by  the  interposition  of  newer  concentric  layers, 
which  diminish  the  diameter  of  the  canals.  In  the  bones  of  half-grown 
animals,  a  part  of  the  bone  is  nearly  in  the  perfect  condition,  while  a 
part  is  new  and  easily  coloured ;  so  that  the  action  of  this  substance 
enables  us  to  distinguish  the  new  from  the  old. 

307.  The  Regeneration  of  Bone,  after  loss  of  its  substance  by  disease 
or  injury,  is  extremely  complete ;  in  fact  there  is  no  other  structure  of 
so  complex  a  nature,  which  is  capable  of  being  so  thoroughly  repaired. 
Although  the  regenerative  power  appears  to  be  so  much  less  in  Verte- 
brated  animals,  than  it  is  in  the  lower  Invertebrata,  yet  it  is  probably 


184  STRUCTURE  AND  ENDOWMENTS  OF  ANIMAL  TISSUES. 

not  at  all  lower  in  reality, — the  new  structures  actually  formed  being 
as  complex  in  the  one  case  as  in  the  other.  It  is  nowhere,  perhaps, 
more  remarkably  manifested,  than  in  the  re-formation  of  nearly  an  entire 
bone,  "when  the  original  one  had  been  lost  by  disease ;  all  the  attach- 
ments of  muscles  and  ligaments,  as  well  as  the  external  form  and  inter- 
nal structure,  being  ultimately  found  as  complete  in  the  new  bone,  as 
they  originally  were  in  that  which  it  has  replaced.  Much  discussion 
has  taken  place  in  regard  to  the  degree,  in  which  the  different  membra- 
nous structures,  that  surround  bone  and  penetrate  its  substance,  par- 
ticipate in  its  regeneration ;  some  having  supposed  the  periosteum  to 
have  the  power  of  itself  forming  new  bone,  others  attributing  the  same 
power  to  the  membrane  lining  the  medullary  cavities.  It  appears  cer- 
tain, however,  that  new  osseous  tissue  may  be  formed  in  a  great  variety 
of  modes.  It  has  been  ascertained  by  Mr.  Paget*  that  it  may  be  pro- 
duced through  the  intermediation  of  perfect  fibrous  tissue,  either  when 
this  previously  existed  as  such  (as  the  periosteum  or  interosseous  mem- 
brane), or  when  it  has  been  newly  formed  by  the  fibrillation  of  the  plastic 
fluid  effused  as  the  material  for  reparation.  The  agency  of  the  perios- 
teum is  seen  in  many  cases  of  necrosis,  in  which  that  membrane  has 
been  completely  detached  from  the  dead  shaft,  and  new  bone  has  been 
generated  from  its  interior.  The  ossification  of  a  newly-produced  fibrous 
membrane  is  believed  by  Mr.  Paget  to  be  the  ordinary  mode  of  repara- 
tion of  fractures  of  the  skull ;  and  it  takes  place  in  a  manner  essentially 
the  same  as  that  of  the  original  intra-membranous  development  of  bone. 
But  new  bone  may  also  be  formed,  according  to  that  most  excellent  ob- 
server, by  ossification  of  the  fibrous  tissue  in  its  rudimental  state  (§  193). 
In  abnormal  bone-growths,  it  sometimes  appears  as  if  the  tissue  had 
been  formed  by  the  ossification  of  cells ;  but  more  commonly  the  calci- 
fication takes  place  in  an  earlier  stage  of  tissue-production,  that  of  the 
"nucleated  blastema,"  in  which  a  granular  osseous  deposit  is  seen,  which 
gradually  increases  so  as  to  form  the  lamellae  of  a  fine  cancellous  texture, 
at  the  same  time  inclosing  the  nuclei,  which  seem  to  occupy  the  places 
afterwards  to  remain  as  the  lacunae.  It  is  seldom  that  the  reparation 
of  bone  takes  place  through  the  intermediation  of  cartilage;  though 
this  is  occasionally  formed,  rather,  perhaps,  in  the  lower  animals  than 
in  the  human  subject. 

308.  The  reparation  of  Bone,  after  disease,  or  injury,  takes  place  ex- 
actly upon  the  same  plan  as  its  first  formation.  A  plastic  or  organiza- 
ble  exudation  is  first  poured  out  from  the  neighbouring  blood-vessels, 
and  this  forms  a  sort  of  bed  or  matrix,  in  which  the  subsequent  processes 
take  place.  At  first  all  new  bone  possesses  a  minutely  cancellous  struc- 
ture, much  like  that  of  the  foetal  bones  in  their  first  construction ;  but 
this  gradually  assimilates  itself  to  the  structure  of  the  bones  which  it 
repairs,  its  outer  portions  acquiring  a  more  compact  laminated  struc- 
ture, while  its  interior  substance  acquires  wider  cancellous  spaces,  and  a 
perfect  medulla.  When  the  shaft  of  a  long  bone  of  an  animal  has  been 
fractured  through,  and  the  extremities  have  been  brought  evenly  to- 
gether, it  is  found  that  the  new  matter  first  ossified  is  that  which  oc- 
cupies the  central  portion  of  the  deposit,  and  which  thus  connects  the 

*  Lectures  on  Reproduction  and  Repair,  Medical  Gazette,  1849. 


r 


FORMATION   OF   TEETH.  185 


i 


medullary  cavities  of  the  broken  ends,  forming  a  kind  of  plug  that 
enters  each.  This  was  termed  by  Dupuytren,  by  whom  it  was  first  dis- 
tinctly described,  the  provisional  callus.  This  is  usually  formed  in  the 
course  of  five  or  six  weeks,  or  less  in  young  subjects ;  but  at  that  period 
the  contiguous  surfaces  of  the  bone  itself  are  not  cemented  by  bony 
union ;  and  the  formation  of  the  permanent  callus  occupies  some  months, 
during  which  the  provisional  callus  is  gradually  absorbed,  and  the  con- 
tinuity of  the  medullary  canal  restored,  in  the  same  manner  as  it  was 
at  first  established.  The  permanent  callus  has  all  the  characters  of  true 
bone.  It  seems  to  have  been  established  by  the  observations  of  Mr. 
Paget,  however,  that  these  statements  do  not  usually  apply  to  the  case 
f  Man ;  in  whom,  when  the  limb  is  kept  at  rest,  the  union  between  the 
actured  ends  is  accomplished  by  ossification  of  the  substance  connect- 
ng  them,  without  the  intermediation  of  a  provisional  callus ;  this  being 
only  formed  when  the  portions  of  the  bone  are  kept  in  continual  move- 
ment. 

809.  The  most  extensive  reparation  is  seen,  when  the  shaft  of  a  long 
bone  is  destroyed  by  disease.     If  violent  inflammation  occur  in  its  tissue, 
;the  death  of  the   fabric  is   frequently  the  consequence, — apparently 
hrough  the  blocking-up  of  the  canals  with  the  products  of  the  inflam- 
atory  action,  and  the  consequent  cessation  of  the  supply  of  nutriment. 
It  is  not  often  that  the  whole  thickness  of  the  bone  becomes  necrosed 
t  once ;  more  commonly  this  result  is  confined  to  its  outer  or  its  inner 
layers.     When  this  is  the  case,  the  new  formation  takes  place  from  the 
art  that  remains  sound ;  the  external  layers,  which  receive  their  vas- 
ular  supply  from  the  periosteum  and  from  the  Haversian  canals  con- 
tinued inwards  from  it,  throwing  out  new  matter  on  their  interior,  which 
is  gradually  converted  into  bone ;  whilst  the  internal  layers,  if  thei/ 
should  be  the  parts  remaining  uninjured,  do  the  same  on  their  exterior, 
deriving  their  materials  from  the  medullary  membrane  and  its  prolon- 
gations into  their  Haversian  canals.     But  it  sometimes  happens  that 
the  whole  shaft  sufi'ers  necrosis ;  and  as  the  medullary  membrane  and 
the  entire  system  of  Haversian  canals  have  lost  their  vitality,  reparation 
can  only  take  place  from  the  periosteuum,  and  from  the  living  bone  at 
the  two  extremities.     This  is  consequently  a  very  slow  process ;  more 
especially  as  the  epiphyses,  having  been  originally  formed  as  distinct 
parts  from  the  shaft,  do  not  seem  able  to  contribute  much  to  the  regene- 
ration of  the  latter. 

310.  We  next  proceed  to  the  Teeth,  which  ar^  organs  of  mechanical 
attrition,  developed  in  the  first  part  of  the  alimentary  canal,  for  the 
purpose  of  comminuting  the  food  conveyed  into  it.  Their  place  of  ori- 
gin is  altogether  difi*erent  from  that  of  bone,  as  they  commence  in  little 
papillary  elevations  of  the  mucous  membrane  covering  the  jaw ;  but  the 
substance  from  which  they  are  formed  is  the  same  primitive  cellular  tissue, 
as  that  in  which  Cartilage  itself  originates.  W^e  may  best  understand 
the  structure  and  development  of  the  Teeth  in  Man,  by  first  inquiring 
into  the  characters  presented  by  those  of  some  of  the  lower  animals, 
and  the  history  of  their  evolution.  In  the  foetal  Shark,  the  first  appear- 
ance of  the  tooth  is  in  the  form  of  a  minute  papilla  on  the  mucous  mem- 
brane covering  the  jaws  ;  the  substance  of  this  papilla  is  composed  of 
spherical  cells,  which  are  imbedded  in  a  kind  of  gelatinous  substance 


186  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

resembling  that  of  incipient  cartilage ;  whilst  its  exterior  is  composed 
of  a  dense,  structureless,  pellucid  membrane.  The  cellular  mass  is  not 
at  first  permeated  by  vessels ;  but  a  small  arterial  branch  is  distributed 
to  each  papilla,  and  spreads  out  into  a  tuft  of  capillaries  at  its  base 
(Fig.  52).   The  papilla  gradually  enlarges,  by  the  formation  of  new  cells 

Fig.  52. 


Yessels  of  Dental  Papilla. 

at  the  part  immediately  adjacent  to  the  blood-vessels,  which  supply  the 
material  requisite  for  .their  development;  and  ^vhen  it  has  acquired 
its  full  size,  the  process  of  calcification  takes  place  by  which  it  is  con- 
verted into  Dentine,  the  substance  most  characteristic  of  teeth. 

811.  This  Dentine,  which  in  the  Elephant's  tusk  is  known  as  Ivory, 
is  a  firm  substance,  in  which  mineral  matter  predominates  to  a  greater 
extent  than  in  bone ;  but  which  still  has  a  definite  animal  basis,  that 
retains  its  form  when  the  calcareous  matter  has  been  removed  by  mace- 
ration in  acid.  In  every  100  parts,  the  animal  matter  forms  about  28 ; 
and  of  the  mineral  portion,  phosphate  of  lime  constitutes  about  64J 
parts,  carbonate  of  lime  5^  parts,  and  phosphate  of  magnesia  and  soda, 
with  chloride  of  sodium,  about  2J  parts.  When  it  is  fractured,  it  seems 
to  possess  a  fibrous  appearance ;  the  fibres  radiating  from  the  centre  of 
the  tooth  towards  its  circumference.  But  when  a  thin  section  of  it  is 
submitted  to  the  microscope,  it  is  seen  that  this  fibrous  appearance  is 
due  to  a  peculiar  structure  in  the  dentine,  which  the  unaided  eye  cannot 
discover.  The  dentinal  substance  is  itself  very  transparent ;  but  it  is 
traversed  by  minute  tubuli,  which  appear  as  dark  lines,  generally  in  very 
close  approximation,  running  from  the  internal  portion  of  the  tooth 
towards  the  surface,  and  exhibiting  numerous  minute  undulations,  and 
sometimes  more  decided  curvatures,  in  their  course  (Fig.  53).     They 


«  ti] 

I 


STRUCTURE  AND  DEVELOPMENT  OP  DENTINE.         187 

bccasionally  divide  into  two  branches,  which  continue  to  run  at  a  little 
distance  from  one  another  in  the  same  direction  ;  and  they  also  fre- 
quently give  off  small  lateral  branches,  which  again  send  off  smaller 
ones.  In  some  animals  the  tubuli  may  be  traced  at  their  extremities 
into  minute  cells,  or  cavities,  analogous  to  the  lacunae  of  bone ;  and  the 
lateral  branchlets  occasionally  terminate  in  such  cavities,  which  are 
called  the  intertubular  cells.  The  diameter  of  the  tubuli  at  their  largest 
part,  averages  l-10,000th  of  an  inch  ;  their  smallest  branches  are  immea- 
surably fine.  It  is  impossible  that  even  the  largest  of  them  can  receive 
blood,  as  their  diameter  is  far  less  than  that  of  the  blood-discs  ;  but  it  is 
probable  that,  like  the  canaliculi  of  bone,  they  may  absorb  nutrient  matter 
from  the  vascular  surface,  with  which  their  internal  extremities  are  in 
relation. 

312.  In  the  Teeth  of  Man  and  of  most  Mammalia,  we  find  the  central 
portion  hollow  ;  and  lined,  in  the  living  tooth,  by  a  vascular  membrane. 
This  cavity,  with  its  vascular  wall,  is  analogous  to  a  large  cancellus  or 
Haversian  canal  of  Bone ;  and,  as  we  shall  presently  see,  it  is  formed 
in  a  similar  manner.     Upon  the  walls  of  the 

cavity,  all  the  tubuli  open ;  and  they  radiate  ^^g-  ^^^ 

from  this  towards  the  surface  of  the  upper 
part  of  the  tooth,  as  shown  in  the  accom- 
panying figure.  The  central  cavity  is  con- 
tinued as  a  canal  through  each  fang  or  root ; 

nd  the  dentinal  tubes  in  like  manner  radiate 
om  this,  towards  the  surface  of  the  fang. — In 

he  teeth  of  many  of  the  lower  animals,  how- 
ever, we  find  a  network  of  canals  extending 
through  the  substance  of  the  tooth,  instead  of 
a  single  cavity ;  and  these  canals  are  fre- 
quently continuous  with  the  Haversian  canals 
of  the  subjacent  bone,  so  that  the  analogy  obiique  section  of  Dentine  of  hu- 
between  the  two  is  complete.  From^  each  S^"tie°pi^M?u3"^^^^^ 
canal  the  dentinal  tubuli  radiate,  just  in  the 

manner  of  the  canaliculi  of  bone  (§  295) ;  and  thus  we  may  regard  a 
tooth  of  this  kind  as  repeating,  in  each  of  the  parts  surrounding  one  of 
these  canals,  the  structure  of  the  human  tooth. 

313.  The  process  by  which  the  cellular  mass,  or  pulpy  of  the  dental 
papilla  becomes  converted  into  the  Dentine  of  the  perfect  tooth,  has  not 
been  so  clearly  made  out,  as  to  be  beyond  all  question.  The  following, 
however,  is  the  account  given  of  it  by  Mr.  Tomes,*  who  has  very  care- 
fully examined  it.  The  dentinal  pulp  is  at  first  composed  of  a  mass  of 
nucleated  cells,  held  together  by  a  meshwork  of  delicate  fibres  and 
bands  constituting  an  imperfect  form  of  areolar  tissue,  the  interspaces 
between  them  being  occupied  by  a  homogeneous  plasma.  In  the  part 
which  is  nearest  to  the  coronal  surface  of  the  tooth  when  calcification  is 
about  to  commence,  the  areolar  tissue  has  usually  disappeared,  and  its 
place  is  occupied  by  a  finely-granular  gelatinous  substance.  The  cells 
are  at  first  disposed  without  any  regularity  in  the  midst  of  this ;  but 


I 


*  Lectures  on  Dental  Physiology  and  Surgery. 


188  STRUCTUKB  AND   ENDOWMENTS   OF   ANIMAL  TISSUES. 

immediately  preceding  the  conversion  of  tlie  pulp  into  dentine,  the  cells 
are  seen  to  enlarge,  arid  to  become  arranged  in  lines,  nearly  parallel  to 
each  other,  and  perpendicular  to  the  coronal  surface  of  the  tooth ;  they 
then  elongate  in  such  a  manner,  that  their  extremities  come  into  appo- 
sition; and  they  finally  coalesce,  so  that  each  row  of  cells  forms  a 
continuous  tube.  Whilst  this  change  is  in  progress,  the  gelatinous 
intercellular  substance  is  becoming  consolidated  by  calcareous  deposit ; 
which  also  hardens  the  thick  walls  of  the  tubes,  so  that  only  their  inte- 
rior, formed  by  the  coalescence  of  the  original  cell  cavities,  remains 
uncondensed,  thus  constituting  the  dentinal  tubuli.  This  process  takes 
place  first  on  the  surface  of  the  pulp,  and  gradually  extends  inwards. 
As  the  more  external  and  larger  cells  become  hardened,  the  inner  ones 
increase  in  size,  assume  the  linear  arrangement,  and  in  their  turn  become 
converted,  with  the  intercellular  substance,  into  tubular  dentine ;  until 
at  last  the  great  bulk  of  the  pulp  is  thus  transformed,  leaving  only  a 
comparatively  small  portion,  which,  with  its  nerves  and  blood-vessels, 
occupies  the  central  cavity  of  the  tooth. 

314.  Thus  the  substance  of  the  outer  portion  of  the  pulp  is  actually 
converted  into  dentine,  and  does  not  form  it  by  a  process  of  excretion^ 
as  was  formerly  supposed.  Sometimes  it  happens  that  the  normal 
changes  are  interrupted,  and  that  some  of  the  original  meshwork  remains 
persistent ;  and  it  is  probably  to  this  that  the  appearance  of  large  cells, 
not  unfrequently  seen  in  Human  teeth  (Fig.  53)  is  due. — Although  in 
the  most  characteristic  form  of  Dentine,  no  blood-vessels  exist,  yet  there 
are  certain  species,  both  among  Mammals,  Eeptiles,  and  Eishes,  in  which 
the  Dentine  is  traversed  by  cylindrical  prolongations  of  the  central  cavity, 
conveying  blood-vessels  into  its  substance ;  and  the  presence  of  these 
medullary  canals,  giving  to  the  Dentine  a  vascular  character,  thus 
increases  its  resemblance  to  bone. — The  central  portion  of  the  pulp  is 
sometimes  converted  into  a  substance  still  more  nearly  resembling  bone, 
having  its  stellate  lacunae  as  well  as  its  vascular  canals.  This  change 
is  normal  or  regular  in  certain  animals,  as  in  the  extinct  Iguanodon  and 
Icthyosaurus,  and  in  the  Cachalot  or  Sperm-whale;  and  the  ossified 
pulp  bears  a  close  resemblance  to  the  bones  of  the  respective  animals 
although  it  is  not  formed  in  continuity  with  them.  A  similar  change 
occurs  in  the  Human  tooth ; — sometimes,  it  would  appear,  rapidly,  as 
the  result  of  disease  ;  but  in  general  more  slowly,  increasing  gradually 
with  the  advance  of  age. 

315.  It  is  not  easy  to  ascertain  the  amount  of  nutritive  change  that 
takes  place  in  the  substance  of  Dentine,  when  it  is  once  fully  formed. 
When  young  animals  are  fed  with  colouring-matter,  it  is  found  to  tinge 
their  teeth,  as  well  as  their  bones ;  and  if  the  tooth  be  in  process  of 
rapid  formation  at  the  time  of  the  experiment,  the  progressive  calcifica- 
tion of  the  pulp  from  without  inwards,  is  marked  by  a  series  of  concen- 
tric lines.  Even  in  the  adult,  some  tinge  will  result  from  a  prolonged 
use  of  this  substance ;  and  it  has  been  noticed  that  the  teeth  of  persons 
who  have  long  suffered  from  Jaundice  sometimes  acquire  a  tinge  of  bile. 
These  facts  show  that,  even  after  the  complete  consolidation  of  the 
Dentine,  it  is  still  pervious  to  fluids :  and  that  in  this  manner  it  may 
draw  into  itself,  from  the  vascular  lining  of  the  pulp-cavity,  a  substance 


SUCCESSION  OF  TEETH. — STRUCTURE   OF  ENAMEL.  189 

ipable  of  repairing  its  structure,  is  proved  by  the  circumstance  that  a 
new  layer  of  hard  matter  is  occasionally  thrown  out  upon  a  surface 
which  has  been  laid  bare  by  caries. 

316.  In  those  simple  teeth  which  consist  solely  of  Dentine,  the  mode 
of  production  already  described, — that  of  the  consolidation  of  a  papilla 
upon  the  mucous  membrane  of  the  mouth, — is  all  which  is  requisite. 
When  the  formation  of  the  tooth  itself  is  complete,  it  may  remain 
attached  only  to  the  mucous  membrane,  which  is  the  case  in  the  Shark, 
or  it  may  grow  downwards,  by  the  addition  of  new  dental  structure  at 
its  base,  until  it  comes  in  contact  with  the  bone  of  the  jaw.  Where  it 
is  only  attached  to  the  mucous  membrane,  as  in  the  Shark,  it  is  very 
liable  to  be  torn  away ;  but  a  new  tooth,  formed  from  a  distinct  papilla, 
is  ready  to  replace  it;  and  this  process  is  continually  repeated,  the 
development  of  new  papillae  being  apparently  unlimited.  On  the  other 
hand,  where  the  root  of  the  tooth  comes  in  contact  with  the  jaw,  it  may 
completely  coalesce  with  it.  which  is  the  case  in  many  Fishes,  the  Ha- 
versian canals  of  the  bones  being  continued  as  medullary  canals  into 
the  dentine ;  or  it  may  send  long  spreading  roots  into  the  bone,  which 
are  united  to  it  at  their  extremities.  In  the  classes  of  Fishes  and  Rep- 
tiles (with  scarcely  any  exceptions)  the  teeth  are  by  no  means  perma- 
nent, as  among  Mammalia ;  but  new  teeth  are  continually  succeeding 
the  old  ones.  The  mode  in  which  these  teeth  originate,  by  small  buds 
from  the  capsules  of  the  preceding,  will  be  understood  when  the  capsular 
development  of  all  the  higher  forms  of  the  dental  apparatus  has  been 
described. 

317.  It  is  obvious  that  there  is  no  provision,  in  the  simple  calcifica- 
tion of  the  dental  papilla,  for  any  variations  of  density,  other  than  those 
which  may  result  from  the  difi'erent  degrees  of  hardness  in  the  substance 
of  the  dentine  itself.  Now  in  the  teeth  of  Man  and  most  other  Mam- 
mals, and  in  those  of  many  Reptiles  and  some  Fishes,  we  find  two  other 
substances,  one  of  them  harder,  and  the  other  softer,  than  Dentine ;  the 
former  is  termed  Enamel ;  and  the  latter  Cementum  or  Orusta  petrosa. 
For  the  development  of  these,  a  peculiar  modification  of  the  apparatus 
is  requisite. 

318.  The  Enamel  is  composed  of  long  prismatic  cells,  exactly  resem- 
bling those  of  the  prismatic  shell-substance  formerly  described  (§  281), 
but  on  a  far  more  minute  scale ;  the  diameter  of  the  cells  not  being 
more,  in  Man,  than  l-5600th  of  an  inch.  The  length  of  the  prisms 
corresponds  with  the  thickness  of  the  layer  of  enapel ;  and-  the  two  sur- 
faces of  this  layer  present  the  ends  of  the  prisms,  which  are  usually  more 
or  less  regularly  hexagonal.  The  quantity  of  animal  matter^  in  the 
enamel  of  the  adult  is  extremely,  minute, — not  above  2  parts  in  100; 
and  it  is  only  at  a  very  early  age  that  the  true  character  of  the  animal 
structure  can  be  distinctly  seen.  Of  the  98  parts  of  mineral  matter  in 
the  enamel,  88  J  consist  (according  to  Berzelius)  of  phosphate  of  lime,  8 
of  carbonate  of  lime,  and  1 J  of  phosphate  of  magnesia.  The  course  of 
the  prismatic  cells  is  more  or  less  wavy ;  and  they  are  marked  by  nu- 
merous transverse  striae,  resembling  those  of  the  prismatic  shell-sub- 
stance, and  probably  originating  in  the  same  cause, — the  coalescence  of 
a  line  of  shorter  cells,  to  form  the  lengthened  prism.     The  Enamel  is 


190 


STRUCTUBE  AND  ENDOWMENTS   OP  ANIMAL  TISSUES. 


Fig.  54. 


usually  destitute  of  tubuli ;  but  Mr.  Tomes  has  shown  that  it  is  occa 
sionally  penetrated  by  prolongations  of  the  tubuli  of  the  dentine,  and 
that  this  peculiarity,  which  is  occasional  and  abnormal  in  Man,  is  cha- 
racteristic of  the  teeth  of  many  Marsupials.  In  density  and  resisting 
power,  the  Enamel  far  surpasses  any  other  organized  tissue,  and  ap- 
proaches some  of  the  hardest  of  mineral  sub- 
stances. In  Man,  and  in  Carnivorous  animals, 
it  covers  the  crown  of  the  tooth  only,  with  a 
simple  cap  or  superficial  layer  of  tolerably  uni- 
form thickness  (Fig.  54,  1),  which  follows  the 
surface  of  the  dentine  in  all  its  inequalities; 
and  its  component  prisms  are  directed  at  right 
angles  to  that  surface,  their  inner  extremities 
resting  in  slight  but  regular  depressions  on  the 
exterior  of  the  dentine.  In  the  teeth  of  many 
Herbivorous  animals,  however,  the  Enamel 
forms  (with  the  Cementum)  a  series  of  vertical 
plates,  which  dip  down  (as  it  were)  into  the  sub- 
stance of  the  dentine,  and  present  their  edges 
alternately  with  it,  at  the  grinding  surface  of 
the  tooth ;  and  there  is  in  such  teeth  no  con- 
tinuous layer  of  dentine  over  the  crown.  The 
purpose  of  this  arrangement  is  evidently  to  pro- 
vide, by  the  unequal  wear  of  these  three  sub- 
stances,— of  which  the  Enamel  is  the  hardest 
and  the  Cementum  the  softest, — for  the  constant 
maintenance  of  a  rough  surface,  adapted  to  tri- 
turate the  tough  vegetable  substances  on  which  these  animals  feed. — 
The  Enamel  is  the  least  constant  of  the  Dental  tissues.  It  is  more  fre- 
quently absent  than  present  in  the  teeth  of  the  class  of  Fishes ;  it  is 
wanting  in  the  entire  order  of  Ophidia  (Serpents)  among  existing  Rep- 
tiles ;  and  it  forms  no  part  of  the  teeth  of  the  Edentata  (Sloths,  &c.) 
and  Cetacea  (Whales)  amongst  Mammals. 

319.  The  Cementum^  or  Orusta  Petrosa,  has  the  characters  of  true 
Bone ;  possessing  its  distinctive  stellate  lacunae  and  radiating  canaliculi. 
Where  it  exists  in  small  amount,  we  do  not  find  it  traversed  by  medullary 
canals ;  but,  like  Dentine,  it  is  occasionally  furnished  with  them,  and 
thus  resembles  Bone  in  every  particular.  These  medullary  canals  enter 
its  substance  from  the  exterior  of  the  tooth ;  and  consequently  pass  to- 
wards those,  which  radiate  from  the  central  cavity  towards  the  surface 
of  the  dentine,  where  it  possesses  a  similar  vascularity,  as  was  remarka- 
bly the  case  in  the  teeth  of  the  extinct  Megatherium.  In  the  Human 
tooth,  however,  the  Cementum  has  no  such  vascularity.  It  forms  a  thin 
layer,  which  envelopes  the  root  of  the  tooth,  commencing  near  the  ter- 
mination of  the  capping  of  Enamel  (Fig.  54,  2).  This  layer  is  very  sub- 
ject to  have  its  thickness  increased,  especially  at  the  extremity  of  the 
fangs,  by  hypertrophy,  resulting  from  inflammation ;  and  sometimes 
large  exostoses  are  thus  formed  (Fig.  54,  4),  which  very  much  increases 
the  difficulty  of  extracting  the  tooth.  When  the  tooth  is  first  developed, 
the  Cementum  envelopes  its  crown,  as  well  as  its  body  and  root ;  but 


Vertical  section  of  human 
molar  tooth :— 1,  enamel ;  2,  ce- 
mentum or  crusta  petrosa;  3, 
dentine  or  ivory;  4,  osseous  ex- 
crescence, arising  from  hypertro- 
phy of  cementum ;  5,  cavity ;  6, 
osseous  cells  at  outer  part  of  den- 
tine. 


I 


FORMATION   OF   DENTAL   CAPSULE.  191 


the  layer  is  very  thin  where  it  covers  the  Enamel,  and  being  soft,  it  is 
soon  worn  away  by  use.  In  the  teeth  of  many  Herbivorous  Mammals, 
it  dips  down  with  the  Enamel  to  form  the  vertical  plates  of  the  interior 
of  the  tooth ;  and  in  the  teeth  of  the  Edentata  as  well  as  of  many  Rep- 
tiles and  Fishes,  it  forms  a  thick  continuous  envelope  over  the  whole  of 
the  surface,  until  worn  away  at  the  crown. 

320.  The  development  of  these  additional  structures  is  provided  for 
by  the  enclosure  of  the  primitive  papilla,  from  which  the  Dentine  is 
formed,  within  a  Capsule,  which,  at  one  period,  completely  covers  it  in : 
between  the  inner  surface  of  the  capsule,  and  the  outer  surface  of  the 
dentinal  papilla,  a  sort  of  epithelium  is  developed,  by  the  calcification 
of  which,  the  Enamel  is  formed ;  and  the  Cementum  is  generated  by 
the  conversion  of  the  capsule  itself  into  a  bony  substance.  The  pro- 
esses  by  which  this  capsular  investment  is  produced,  and  the  tooth 

completed  and  evolved,  will  now  be  briefly  described,  as  they  occur  in 
the  Human  foetus. 

321.  The  dental  papillae  begin  to  make  their  appearance,  at  about 
the  seventh  week  of  embryonic  life,  upon  the  mucous  membrane  cover- 
ing the  bottom  of  a  deep  narrow  groove  (Fig.  b^,  a\  that  runs  along 
the  edge  of  the  jaw  (Fig.  bb,  h) ;  and  during  the  tenth  week,  processes 
from  the  sides  of  this  "  primitive  dental  groove,"  particularly  the  ex- 
ternal one,  begin  to  approach  one  another,  so  as  to  divide  it,  by  their 
meeting,  into  a  series  of  open  follicles,  at  the  bottom  of  which  the  pa- 
pillae may  still  be  seen.  At  the  thirteenth  week  all  the  follicles  being 
completed,  the  papillae,  which  were  at  first  round  blunt  masses  of  cells, 
began  to  assume  forms  more  characteristic  of  the  teeth  which  are  to  be 
developed  from  them ;  and  by  their  rapid  growth,  they  protrude  from 

Fig.  55. 


Successive  stages  of  the  development  of  the  deciduous  or  temporary  teeth,  and  of  the  origin  of  the 
sacs  of  the  permanent  set.  ' 

the  mouths  of  the  follicles  (Fig.  bb,  c).  At  the  same  time,  the  edges 
of  the  follicles  are  lengthened  into  little  valve-like  processes,  or  oper- 
cula,  which  are  destined  to  meet  and  form  covers  to  the  follicles  (Fig. 
bb,  d).  There  are  two  of  these  opercula  in  the  Incisive  follicles,  three 
for  the  Canines,  and  four  or  five  for  the  Molars.  And  by  the  fourteenth 
week,  the  two  lips  of  the  dental  groove  meet  over  the  mouths  of  the 
follicles,  so  as  completely  to  enclose  each  papilla  in  a  distinct  capsule 
(Fig.  bb,  e).  At  this  period,  before  the  calcification  of  the  primitive 
pulps  commences,  a  provision  is  made  for  the  production  of  the  second 
or  permanent  molars;  whose  capsules  originate  in  buds  or  offsets  from 
the  upper  part  of  the  capsules  of  the  temporary  or  milk-teeth  (Fig.  55,/). 


192  STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

These  offsets  are  in  the  condition  of  open  follicles,  communicating  with 
the  cavity  of  the  primitive  tooth  ;  but  they  are  gradually  closed  in,  and 
detached  altogether  from  the  capsules  of  the  milk-teeth  (Fig.  55,  g,  h,  i), 

322.  Soon  after  the  closure  of  the  follicles  of  the  Milk-teeth,  the  con- 
version of  the  cells  of  the  original  papilla  into  Dentine  commences,  ac- 
cording to  the  method  already  described  (§  313).  Whilst  this  is  going 
on,  the  follicles  increase  in  size,  so  that  a  considerable  space  is  left  be- 
tween their  inner  walls  and  the  surface  of  the  dental  papillae ;  which 
space  is  filled  up  with  a  gelatinous  granular  matter,  the  Enamel  pulp. 
The  portion  of  this  which  is  converted  into  enamel,  however,  is  very 
small ;  being  only  a  thin  layer,  which  is  left  on  the  inner  surface  of  the 
capsule  after  the  remainder  has  disappeared.  The  interior  of  the  dental 
saCj  at  the  time  when  the  conversion-process  has  reached  the  base  of  the 
dentinal  pulp,  is  in  the  villous  and  vascular  condition  of  a  Mucous  mem- 
brane,— which  indeed  it  really  is,  having  been,  as  we  have  seen,  once 
continuous  with  the  lining  of  the  mouth ;  and  the  layer  of  prismatic  cells 
which  covers  its  free  surface,  and  by  the  calcification  of  which  the  enamel 
is  produced,  may  be  regarded  as  an  epithelium.  The  completion  of  the 
Enamel,  and  the  ossification  of  the  capsule  so  as  to  form  the  Cementum, 
take  place  at  a  subsequent  period. 

323.  We  have  thus  seen  that  the  history  of  the  first  development  of 
the  Human  teeth  may  be  divided  into  three  stages,  the  papillary,  the 
follicular,  and  the  saccular.  The  papillary  corresponds  precisely  with 
the  complete  mode  of  dental  development  in  the  Shark  and  other  Fish, 
— as  already  mentioned.  The  follicular,  which  commences  with  the  en- 
closure of  the  papillae  in  open  follicles,  and  terminates  when  the  papillae 
are  completely  hidden  by  the  closure  of  the  mouths  of  those  follicles, 
has  also  its  permanent  representation  in  the  development  of  the  teeth 
of  many  Reptiles  and  Fishes ;  the  primitive  papilla3  of  which,  though 
enclosed  in  follicles,  are  never  covered  in  at  the  summit,  and  thus  free 
themselves  from  their  envelopes  by  simply  growing  upwards  through 
their  open  mouths.  But  in  Man,  and  in  all  other  animals  which  agree 
with  him  in  going  on  to  the  saccular  stage,  there  must  also  be  an  erup- 
tive stage,  which  consists  in  the  bursting-forth  of  the  tooth  from  the 
enclosing  capsule ;  the  summit  of  the  tooth  being  carried  against  the  lid 
of  the  sac,  by  the  growth  of  its  roots  (Fig.  55,  h).  By  the  continuance 
of  the  same  growth,  the  teeth  are  caused  to  penetrate  the  gum,  and  are 
gradually  raised  above  its  surface  (Fig.  55,  i). 

324.  All  the  permanent  teeth,  which  are  destined  to  replace  the 
temporary  set,  originate,  as  already  stated,  in  buds  or  ofi'sets  from  the 
capsules  of  the  latter.  But  behind  the  last  temporary  molars,  which 
are  replaced  by  the  permanent  bicuspids,  three  permanent  molars  are 
to  be  developed,  on  each  side  of  either  jaw.  The  first  of  these  is  formed 
on  precisely  the  same  plan  with  the  milk-teeth ;  but  is  not  completed 
until  a  later  period.  The  capsule  of  the  second  is  formed  at  a  later 
period  from  that  of  the  first,  by  a  process  of  budding  exactly  analogous 
to  that,  by  which  the  other  permanent  capsules  are  formed  from  the 
corresponding  temporary ;  and  at  a  still  later  period,  the  capsule  of  the 
third  permanent  molar  is  formed  as  a  bud  from  that  of  the  second.  The 
evolution  of  this  molar  does  not  usually  take  place,  until  the  system 


DEVELOPMENT  AND   RENEWAL   OF  TEETH. 


193 


has  acquired  its  full  development ;  and  the  process  of  budding  then 
ceases  in  Man, — being  limited  to  a  single  act  of  reproduction  in  the 
case  of  the  ordinary  Milk-teeth,  and  to  a  double  one  in  that  of  the  first 
permanent  Molar.  In  many  animals  of  the  lower  classes,  however,  the 
process  goes  on  through  the  whole  of  life  without  any  limit ;  the  newly- 
formed  teeth,  however,  usually  taking  the  places  of  those  of  the  previous 
set,  and  not  being  developed  at  their  sides  like-  the  second  and  third 
permanent  molars  of  Man.  By  a  process  of  this  kind,  the  continual 
renewal  of  the  Teeth  takes  place  in  those  Reptiles  and  Fishes,  whose 
dentition  goes  on  to  the  saccular  stage  ;  in  those  at  which  it  stops  at  the 
papillary,  the  successive  teeth  are  formed  from  new  and  independent 
papillae.  The  analogy  between  the  continued  succession  of  teeth  in  the 
lower  Vertebrata,  by  the  gemmiparous  reproduction  of  their  capsules, 
and  the  development  of  the  capsules  of  the  permanent  teeth  of  Man 
from  those  of  the  temporary  set,  is  made  further  evident  by  the  fact, 
that  a  third  set  occasionally  makes  its  appearance  in  persons  advanced 
in  life  ;  the  development  of  which  would  not  be  intelligible,  if  we  could 
not  refer  it  to  the  continuance  of  the  same  process  in  the  other  capsules, 
as  that  which  regularly  takes  place  to  a  limited  extent  in  the  permanent 
molars  of  Man,  and  which  goes  on  without  limit  through  the  whole  lives 
of  the  lower  Vertebrata. 

325.  The  chief  exception  to  the  rule,  that  no  Reptiles  or  Fishes  have 
permanent  teeth,  is  found  in  the  curious  Dicynodon ;  an  extinct  Reptile 
which  had  two  large  tusks  growing  from  persisteTit  pulps,  like  those  of 
the  Elephant,  the  front  teeth  of  the  Rodentia,  and  the  grinders  of  the 
Edentata.  In  such  teeth,  the  base  of  the  pulp  remains  unconverted, 
and  a  new  development  of  cells  is  continually  taking  place  in  that  situa- 
tion ;  these  new  cells  are  in  their  turn  converted  into  dentine,  in  con- 
tinuity with  that  previously  formed ;  and  thus  the  tooth  or  tusk  is  con- 
tinually lengthening  at  its  base,  in  a  degree  which  compensates  for  its 
usual  wear  at  its  summit.  If  anything  should  prevent  that  wear, — 
as  when  the  opposite  tooth  has  been  broken  ofi", — there  is  an  absolute 
increase  in  the  length  of  the  tooth,  from  the  continued  growth  at  its 
base ;  which  may  become  a  source  of  great  inconvenience  to  the  animal. 
There  is  nothing,  in  the  Human  subject,  at  all  analogous  to  this  mode 
of  development  from  persistent  pulps  ;  the  process  being  checked  by  the 
closure  of  the  root  around  the  base  of  the  pulp,  which  obstructs  the 
supply  of  blood  it  receives. 

326.  The  following  table  shows  the  usual  periods  at  which  the  diffe- 
rent teeth  of  the  two  sets  first  show  themselves  above  the  gum.  It  must 
be  borne  in  mind,  however,  that  these  periods  are  subject  to  very  great 
variation ;  and  that  the  average  alone  can  therefore  be  expressed. 


TEMPORARY  0R_  DECIDUOUS  TEETH. 

Months 

Central  Incisors, 
Lateral  Incisors, 


PERMANENT  TEETH. 


Anterior  Molars, 
Canines,  . 
Posterior  Molars, 


i 
8—10 
12  —  13 
14  —  20 
18  —  36 


I 


First  Molar,  . 
Central  Incisors, 
Lateral  Incisors, 
First  Bicuspid, 
Second  Bicuspid, 
Canines, 
Second  Molars, 
Third  Molars, 


Years. 
6Jt0     7 

7  —  8 

8  —   9 
9—10 

10   —11 
12   -^12^ 
12i  — 14 
1-6   —30 


13 


194  STRirCTURB  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

327.  We  have  seen  that  the  teeth  are  formed,  in  the  first  instance, 
upon  the  surface  of  the  Mucous  membrane  of  the  mouth ;  and  conse- 
quently they  really  form  a  part  of  the  external  or  dermo-skeleton,  and 
not  of  the  internal  or  osseous  skeleton.  They  correspond,  therefore, 
with  the  external  skeletons  of  the  Invertebrata ;  and  thus  the  analogy 
which  has  been  pointed  out,  between  the  enamel  of  teeth  and  the  pris- 
matic cellular  substance  of  the  shells  of  Mollusca,  and  between  the  den- 
tine and  the  shells  of  the  higher  Crustacea,  holds  good  also  in  regard 
to  the  situation  of  these  structures.  Although  the  teeth  are  the  only 
ossified  portions  of  the  dermo-skeleton  in  Man,  we  find  the  body  par- 
tially or  completely  enclosed  in  an  armour  of  bony  scales  or  plates,  in 
certain  Mammalia,  Reptiles,  and  Fishes ;  and  in  some  species  of  the 
last-named  class,  which  have  now  ceased  to  exist,  the  scales  seem  to 
have  had  the  texture  of  Enamel. 

328.  In  connexion  with  the  Teeth,  the  structure  and  development  of 
the  Hair  may  be  described ;  this  substance  being  generated  very  much 
in  the  same  manner  as  dentine, — by  the  conversion  of  a  pulp  enclosed 
in  a  follicle ;  though  the  product  of  the  transformation  is  difierent. 
The  Hair-follicle  is  formed  by  the  inversion  of  the  Skin,  as  the  Tooth- 
follicle  is  by  an  inversion  of  the  Mucous  membrane ;  and  it  is  lined  by 
a  continuation  of  the  epidermis.  From  the  bottom  of  the  follicle,  a 
sort  of  papilla  rises  up,  formed  of  cells ;  the  exterior  of  this,  which  is 
the  densest  part,  is  known  as  the  hulh ;  whilst  the  softer  interior  is 
termed  the  pulp.  The  follicle  itself  is  extremely  vascular ;  and  even 
the  bulb  is  reddened  by  a  minute  injection ;  though  no  distinct  vessels 
can  be  traced  into  it. — It  has  been  imagined  until  recently,  that  the 
Hair,  like  the  other  extra-vascular  tissues,  is  a  mere  product  of  secre- 
tion ;  its  material,  which  is  chiefly  horny  matter  of  the  same  composition 
with  that  of  the  epidermis  and  its  other  appendages  (§  227),  being  ela- 
borated from  the  surface  of  the  pulp.  This,  however,  proves  to  be  a 
very  erroneous  account  of  it ;  as  is  shown  by  the  results  of  microscopic 
inquiries  into  its  structure.  Although  the  Hairs  of  difierent  animals 
vary  considerably  in  the  appearances  they  present,  we  may  generally 
distinguish  in  them  two  elementary  parts  ; — a  cortical  or  investing  sub- 
stance, of  a  fibrous  horny  texture ;  and  a  medullary  or  pith-like  sub- 
stance occupying  the  interior.  The  fullest  development  of  both  sub- 
stances is  to  be  found  in  the  spiny  hairs  of  the  Hedge-hog,  and  in  the 
quills  of  the  Porcupine,  which  are  but  hairs  on  a  magnified  scale.  The 
cortical  substance  forms  a  dense  horny  tube,  to  which  the  firmness  of 
the  structure  seems  chiefiy  due ;  whilst  the  medullary  substance  is  com- 
posed of  an  aggregation  of  very  large  cells,  which  seem  not  to  possess 
any  fluid  contents  in  the  part  of  the  hair  that  is  completely  formed. 
The  structure  of  the  feather  of  Birds  is  precisely  analogous :  the  cor- 
tical horny  tube  existing  alone  in  the  quill,  but  being  filled  with  a  cel- 
lular medulla  in  the  stem  of  the  feather  itself.  The  smaller  hairs  of 
the  Sable  (Fig.  ^^^  b)  show  the  cortical  and  medullary  substances  in  a 
very  characteristic  form ;  the  former  being  here  plainly  seen  to  be  made 
up  of  flattened  imbricated  cells  resembling  those  of  the  epidermis  ;  whilst 
the  cells  of  which  the  latter  is  composed  are  nearly  globular.  In  the 
hair  of  the  Musk-deer  (Fig.  m,  a),  we  find  the  medullary  substance  to 


STRUCTURE  AND  DEVELOPMENT  OF  HAIR. 


195 


composed  of  an  assemblage  of  cells  whose  walls  are  flattened  against 
each  other,  as  in  a  Vegetable  pith;  whilst  the  cortical  envelope  is 
scarcely  distinguishable.     In  the  hair  of  the  Mouse  and  other  small 

Fig.  56. 


1  ■  w] 


structure  of  Hair: — a,  hair  of  Musk-deer,  consisting  almost  entirely  of  polygonal  cells ;  b,  hair  of  Sable, 
showing  large  rounded  cells  in  its  interior,  covered  by  imbricated  scales  or  flattened  cells. 

Eodents,  we  see  the  horny  tube  crossed  at  intervals  by  partitions,  which 
are  sometimes  complete,  sometimes  only  partial ;  these  are  the  walls  of 
the  single  or  double  line  of  cells,  of  which  the  medullary  substance  is 
made  up. 

329.  In  the  Human  hair,  the  representation  of  the  cortical  envelope 
f  the  hair  of  other  animals  is  found  in  a  thin  transparent  horny  film 
hich  is  composed  of  flattened  cells  or  scales,  arranged  in  an  imbricated 
anner,  their  edges  forming  delicate  lines  upon  the  surface  of  the  hair, 
which  are  sometimes  transverse,  sometimes  oblique,  and  sometimes 
apparently  spiral  (Fig.  57,  a).  Within  this,  we  find  a  cylinder  of 
fibrous  texture,  which  forms  the  principal  part  of  the  shaft  of  the  hair, 


structure  of  the  Human  Hair :— A,  external  surface  of  the  shaft,  showing  the  transverse  8tria9  and  jagged' 
boundary,  caused  by  the  imbrications  of  the  scaly  cortex ;  B,  longitudinal  section  of  the  shaft,  showing  the 
fibrous  character  of  the  medullary  substance,  and  the  arrangement  of  the  pigmentary  matter;  C,  transverse 
section,  showing  the  distinction  between  the  cortical  and  medullary  substances  and  the  central  collection  of 
pigmentary  matter ;  D,  similar  transverse  section  without  the  dark  centre. 

and  it  is  in  the  centre  alone,  which  is  frequently  more  distinctly  cellular, 
that  we  find  any  close  resemblance  to  the  ordinary  condition  of  the  me- 
dullary substance.  The  constituent  fibres  of  the  shaft  are  marked  out 
by  delicate  longitudinal  striae,  which  may  be  traced  in  vertical  sections 
of  the  hair  (b)  :  but  they  may  be  still  more  completely  demonstrated  by 


196  STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

crushing  the  hair,  after  it  has  been  macerated  for  some  time  in  dilute 
acid.  In  dark  hairs,  the  pigmentary  granules  are  frequently  scattered 
between  the  fibres :  but  they  are  frequently  found  in  greater  abundance 
in  the  central  cells,  where  they  form  a  dark  spot  in  the  middle  of  the 
transverse  section  (c).  Sometimes,  however,  no  such  collection  is  seen ; 
and  whatever  pigmentary  matter  exists  in  the  hair  is  equally  diffused 
through  the  whole  of  it,  or,  is  even  accumulated  rather  towards  its  exte- 
rior (d).  This  colouring  matter  seems  related  to  Hsematine ;  it  is 
bleached  by  chlorine ;  and  when  it  gives  a  dark  hue  to  the  hair,  it  usually 
contains  a  good  deal  of  iron. 

330.  The  fibres  of  which  the  chief  part  of  the  shaft  is  made  up  are 
probably  cells,  which  have  become  elongated  by  the  process  already 
noticed  (§  193),  and  which  have  at  the  same  time  secreted  horny  matter 
into  their  interior.  This  change  is  continually  going  on  in  the  hulh  of 
the  hair,  at  the  base  of  the  part  previously  completed ;  and  by  the  pro- 
gressive formation  of  new  cells  in  the  bulb,  a  constant  growth  of  the 
shaft  is  provided  for.  The  central  medullary  substance  is  rather 
derived  from  the  cells  of  the  pulp,  in  which  a  continuous  growth  goes 
on,  at  the  same  rate  with  that  of  the  bulb.  The  imbricated  layer  of 
cells  which  forms  the  true  cortical  substance  may  be  said  to  be  a  pro- 
longation of  the  ordinary  Epidermis  over  the  surface  of  the  hair,  being 
developed  from  the  external  layer  of  the  bulb,  where  it  is  continuous 
with  the  epidermic  lining  of  the  follicle.  Thus  the  Hair  is  constantly 
undergoing  elongation  by  the  addition  of  new  substance  at  its  base ; 
precisely  in  the  same  manner  as  the  teeth  of  certain  Mammals  grow 
from  persistent  pulps.  The  part  once  formed  usually  undergoes  no 
subsequent  alteration ;  but  there  is  evidence  that  it  may  be  afi"ected  by 
changes  at  its  base,  the  efi'ect  of  which  is  propagated  along  its  whole 
extent.  Thus,  it  is  well  known  that  cases  are  not  unfrequent,  in  which, 
under  the  influence  of  strong  mental  emotion,  the  whole  of  the  hair  has 
been  turned  to  gray,  or  even  to  a  silvery  white,  in  the  course  of  a  single 
night ;  a  change  which  can  scarcely  be  accounted  for  in  any  other  way 
than  by  supposing  that  a  fluid,  capable  of  chemically  afi*ecting  the 
colour,  is  secreted  at  the  base  of  the  hair,  and  transmitted  by  imbibition 
through  the  medullary  substance  to  the  opposite  extremity.  The  know- 
ledge of  the  organized  structure  of  hair  enables  us  better  to  understand 
Bome  of  the  effects  of  disease,  and  especially  of  that  peculiar  aff'ection 
termed  Plica  Polonica.  The  hair  of  individuals  suff'ering  from  it  is  dis- 
posed to  split  into  fibres,  often  at  a  considerable  distance  from  the 
roots,  and  to  exude  a  glutinous  substance ;  and  these  two  causes  unite 
in  occasioning  that  peculiar  matting  of  the  hair,  which  has  given  origin 
to  the  name  of  the  disease.  In  the  hair  thus  aff'ected,  there  is  evidently 
a  power  of  transmitting  fluid  absorbed  at  the  roots :  and  it  is  said  that 
even  blood  exudes  from  the  stumps,  when  the  hairs  are  cut  off  clos€  to 
the  skin. 

6.    Of  Cells  coalesced  into  Tubes  with  Secondary  Deposit. 

331.  Most  of  the  tissues  which  have  been  hitherto  described,  diff"er  in 
no  essential  particulars  from  those  of  Plants ;  the  chief  departure  from 


MUSCULAR   FIBRE.  197 

;lie  forms  presented  by  the  latter,  being  in  the  Fibrous  tissues,  which, 
as  already  observed,  are  introduced  for  the  sake  of  facilitating  the 
movements  of  the  several  parts  of  the  structure,  one  upon  the  other. 
The  various  cellular  tissues  find  their  exact  representatives  in  those  of 
the  Vegetable  fabric;  and  the  denser  parts  of  the  Animal,  such  as 
Bone,  Cartilage,  &c.,  are  represented  by  the  solid  substances  formed 
by  the  Plant  in  the  heart-wood  of  the  stem,  the  stone  of  fruits,  &c., 
these  substances  acquiring  their  density  in  precisely  the  same  manner 
with  the  Osseous  tissues,  by  the  secreting-  action  of  their  own  cells, 
which  draw  a  solidifying  material  from  the  general  circulating  fluid. 
But  we  now  come  to  two  tissues  of  the  highest  importance  in  the  Animal 
fabric,  the  presence  of  which  is,  indeed,  its  distinguishing  characteristic. 
These  are  the  Muscular  and  the  Nervous  tissues.  The  former  is  the 
one  by  w^hich  all  the  sensible  movements  of  the  body  are  effected ;  and 
the  latter  furnishes  the  instrument  by  which  sensations  are  received, 
and  by  which  the  will  excites  the  muscles  to  action,  besides  serving  as 
the  medium  for  other  operations,  in  which  motion  is  produced  without 
the  intervention  of  either  sensation  or  will.  These  tissues,  with  the 
apparatus  of  bones  and  joints  on  which  the  muscles  act,  constitute  the 
purely  animal  portion  of  the  fabric  ;  and  if  a  being  could  be  constructed, 
i  in  which  they  should  be  capable  of  continued  activity  without  any  other 
■■issistance,  it  would  be  in  all  essential  particulars  an  Animal.  But,  as 
l^ftre  shall  presently  see,  the  plans  on  which  these  tissues  are  formed,  in 
IHpEict,  the  very  conditions  of  their  existence  and  activity,  are  such,  that 
f^^hey  require  constant  nutrition  and  re-formation ;  so  that  the  Animal 
I  cannot  exist  without  an  apparatus  for  preparing,  circulating,  and  main- 
taining in  constant  purity,  a  fluid  by  which  nutrient  operations  may  be 
effected,  and  which  shall  also  be  the  means  of  carrying  off  the  products 
\  of  the  waste  consequent  upon  the  action  of  those  tissues.  This  appa- 
i  ratus  constitutes  the  Vegetative  portion  of  the  frame,  the  elementary 
,  parts  concerned  in  which  have  been  already  noticed. 
I  332.  When  we  examine  an  ordinary  Muscle  with  the  naked  eye,  we 

observe  that  it  is  made  up  of  a  number  of  fasciculi  or  bundles  of  fibres  ; 
!      which  are  arranged  side  by  side  with  great  regularity,  in  the  direction 
j       in  which  the  muscle  is  to  act,  and  which  are  united  by  areolar  tissue. 
j      These  fasciculi  may  be  separated  into  smaller  parts,  which  appear  like 
j      simple  fibres ;  but  when  these  are  examined  by  the  microscope,  they 
I       are  found  to  be  themselves  fasciculi,  composed  of  minuter  fibres  bound 
I       together  by  delicate  filaments  of  areolar  tissue.;    By  carefully  sepa- 
!       rating  these,  we  may  obtain  the  ultimate  Muscular  Fibre.     This  fibre 
I       exists  under  two  forms,  the  striated  and  the  non-striated;  the  former 
'       makes  up  the  whole  substance  of  those  muscles  over  which  the  will  has 
control,  or  which  are  usually  called  into  operation  through  the  nerves ; 
whilst  the  latter  exists  in  the  muscles  which  the  will  cannot  influence, 
and  which  are  excited  to  contraction  by  stimuli  that  act  directly  upon 
them.     The  muscles  of  the  former  class  minister  especially  to  the  animal 
functions ;  those  of  the  latter  to  the  functions  of  organic  or  vegetative 
life.     The   appearance  presented   by  the  striated  fibres  of  ordinary 
muscles  is  shown  in  Fig.  58 ;  that  of  the  non-striated  fibres  of  the 
muscles  of  organic  life,  in  Fig.  59. 


UB9 


STRUCTURE  AND  ENBOWMENTS   OF  ANIMAL  TISSUES. 


333.  When  the  striated  fibre,  which  must  be  considered  as  the  highest 
form  of  Muscular  tissue,  is  more  closely  examined,  it  is  seen  to  consist 
of  a  delicate  tubular  sheath,  quite  distinct  on  the  one  hand  from  the 
areolar  texture  which  binds  the  fibres  into  fasciculi,  and  equally  distinct 


Fig.  68. 


Fig.  59. 


Fasciculus  of  striated  Muscular 
Fibre,  showing  at  a  the  trans- 
verse striae,  and  at  6,  the  longi- 
tudinal striae. 


Non-striated  Muscular  Fibre; 
at  b,  in  its  natural  state;  at  a, 
showing  the  nuclei  after  the  action 
of  acetic  acid. 


from  the  internal  substance  of  the  fibre.  This  cannot  always  be  brought 
into  view,  on  account  of  its  transparency;  it  becomes  most  evident, 
when,  as  occasionally  happens,  the  contents  of  the  fibre  are  separated 
transversely  by  the  drawing  apart  of  its  extremities  without  the  rupture 
of  the  sheath ;  but  it  may  also  be  sometimes  seen  rising  up  in  wrinkles 
upon  the  surface  of  the  fibre,  when  the  latter  is  in  a  state  of  contraction. 
This  membranous  tube,  which  has  been  termed  the  Myolem7na,  has 
nothing  to  do  with  the  production  of  the  striae,  these  being  due,  as  will 
be  presently  shown,  to  the  peculiar  arrangement  of  its  contents.  It  is 
not  perforated  either  by  nerves  or  capillary  vessels,  and  forms,  in  fact, 
a  complete  barrier  between  the  real  elements  of  Muscular  structure  and 
the  surrounding  parts.  That  it  has  no  share  in  the  contraction  of  the 
fibre  is  evident  from  the  fact  just  mentioned,  in  regard  to  its  wrinkled 
aspect  when  the  fibre  is  shortened. 

334.  Although  Muscular  Fibres  are  commonly  described  as  cylin- 
drical in  form,  yet  they  are  in  reality  rather  polygonal,  their  sides 
being  flattened  against  those  of  the  adjoining  fibres  (Fig.  62).  In  some 
instances,  the  angles  are  sharp  and  decided ;  in  others  they  are  rounded 
ofi",  so  as  to  leave  spaces  between  the  contiguous  fibres,  for  the  passage 
of  vessels.  In  Insects,  the  fibres  often  present  the  form  of  flattened 
bands,  on  which  the  transverse  striae  are  very  beautifully  marked.  The 
size  of  the  fibres  is  subject  to  great  variation,  not  merely  in  diff'erent 
classes  of  animals,  but  in  difi'erent  species,  in  diff'erent  sexes  of  the  same 
species,  and  even  in  diff'erent  parts  of  the  same  muscle.     Thus  Mr. 


STRIATED   MUSCULAR   FIBRE. 


199 


lowman  estimates  the  average  diameter  of  the  fibres  in  the  Human 
male  at  l-352d  of  an  inch ;  the  largest  being  l-192d,  and  the  smallest 
l-507th.  In  t}iQ  female^  he  found  the  average  to  be  l-454th  of  an  inch ; 
whilst  the  largest  was  l-384th,  and  the  smallest  l-615th.  The  average 
size  of  the  Muscular  fibre  is  greater  among  Reptiles  and  Fishes,  than 
in  other  Vertebrata ;  but,  on  the  other  hand,  the  extremes  are  much 
wider.  Thus  its  dimensions  vary  in  the  Frog  from  1-lOOth  to  1-lOOOth 
of  an  inch  ;  and  in  the  Skate  from  l-65th  to  l-300th. 

335.  When  the  striated  Muscular  Fibre  is  examined  still  more  closely, 
it  is  found  to  contain  an  assemblage  of  very  minute  elements,  which 
appear  to  be  flattened  disk-like  cells,  of  very  uniform  size.  These 
primitive  particles  are  adherent  to  each  other  both  by  their  flat  surfaces, 
and  by  their  edges.  The  former  adhesion  is  usually  the  most  powerful, 
and  causes  the  substance  of  the  fibre,  when  it  is  broken  up,  to  present 
itself  in  the  form  of  delicate  fibrillce,  each  of  which  is  composed  of  a 
single  row  of  the  primitive  particles  (Fig.  60).  On  the  other  hand,  the 
lateral  adhesion  is  sometimes  the  stronger,  and  causes  the  fibre  to  break 
across  into  disks,  each  of  which  is  composed  of  a  la^er  of  the  primitive 


Fig.  60. 


striated  muscular  fibre  separating  into  fibrillae  (from  a  Terebratula). 

particles  (Fig.  61).  That  the  fibre  is  a  solid  collection  of  these  elemen- 
tary parts,  and  not  hollow  in  the  centre,  as  some  have  supposed,  is 
shown  by  making  a  thin  transverse  section  of  a  fasciculus  (Fig.  62) ;  by 
which  also  the  polygonal  form  of  the  fibre  is  made  apparent. 


Fig.  61. 


Fig.  62. 


An  ultimate  fibre,  in  which  the 
transverse  splitting  into  disks,  in 
the  direction  of  the  striation  of 
the  ultimate  fibrils,  is  seen. 


Transverse  section  of  ultimate  fibres  of 
the  biceps.  In  this  figure  the  polygonal 
form  of  the  fibres  is  seen,  and  their  com- 
position of  ultimate  fibrils. 


336.  When  the  fibrillse  are  separately  examined,  under  high  magni- 
fying power,  they  are  seen  to  present  a  cylindrical  or  slightly-beaded 


200 


STRUCTURE  A'SB   ENDOWMENTS   OP  ANIMAL  TISSUES. 


form,  and  to  be  made  up  of  a  linear  aggregation  of  distinct  cells.  We 
observe  the  same  alternation  of  light  and  dark  spaces,  as  when  the 
fibrillse  are  united  into  fibres  or  into  small  bundles;  but  it  may  be 
distinctly  seen,  that  each  light  space  is  divided  by  a  transverse  line ; 
and  that  there  is  a  pellucid  border  at  the  sides  of  the  dark  spaces,  as 
well  as  between  their  contiguous  extremities  (Fig.  63).  This  pellucid 
border  seems  to  be  the  cell-wall ;  the  dark  space  enclosed  by  it  (which 
is  usually  bright  in  the  centre)  being  the  cavity  of  the  cell,  which  is 
filled  with  a  highly-refracting  substance.  When  the  fibril  is  in  a  state 
of  relaxation,  las  seen  at  a,  the  diameter  of  the  cells  is  greatest  in  the 
longitudinal  direction :  but  when  it  is  contracted,  the  fibril  increases  in 
diameter  as  it  diminishes  in  length ;  so  that  the  transverse  diameter  of 
each  cell  becomes  equal  to  the  longitudinal  diameter,  as  seen  at  J ;  or 
even  exceeds  it.  Thus  the  act  of  Muscular  contraction  seems  to  con- 
sist in  a  change  of  form  in  the  cells  of  the  ultimate  fibril- 
Fig.  63.  ige^  consequent  upon  an  attraction  between  the  walls  of 
their  two  extremities ;  and  it  is  interesting  to  observe,  how 
very  closely  it  thus  corresponds  with  the  contraction  of 
certain  Vegetable  tissues,  of  which  the  component  cells 
(§  345)  appear  to  produce  a  movement,  when  they  are 
irritated  by  means  of  a  similar  change  of  form.  The 
essential  difierence,  therefore,  between  the  muscular  tissue 
of  Animals,  and  the  contractile  tissues  of  Plants,  consists 
in  the  subjection  of  the  former  to  nervous  influence  (§  353). 
The  diameter  of -the  ultimate  fibrillae  will  of  course  be  sub- 
ject to  variations,  in  accordance  with  their  contracted  or 
relaxed  condition;  but  seems  to  be  otherwise  tolerably 
uniform  in  difi*erent  animals,  being  for  the  most  part  about 
l-10,000th  of  an  inch.  It  has  been  observed,  however, 
as  high  as  l-5000th  of  an  inch,  and  as  low  as  l-20,000th, 
even  when  not  put  upon  the  stretch.  The  average  dis- 
tance of  the  striae,  too,  is  nearly  uniform  in  difi'erent  ani- 
mals; though  considerable  variations  present  themselves 
ultimate  '^fibriii*  lu  cvcry  individual,  and  in  difi'erent  parts  of  the  same 
cniarfl*b?e:-^ra  J^^scle.  Thus  the  maximum  distance  varies  in  difi'erent 
SiV  rdal^  animals  from  l-15,000th  to  l-20,000th  of  an  inch ;  the  mini- 
tion;  fc,  a  fibril  in  mum  from  l-7500th  to  l-4500th  of  an  inch;  while  the 
coniiSstionr^ '*  mean  does  not  depart  widely  in  any  instance  from 
l-10,000th.  . 
337.  The  Muscular  tissue  of  Organic  life  is  very  difi'erent  from  that 
which  has  been  now  described.  It  exists  under  two  forms ;  that  of 
fibres  and  that  of  cells.  The  fibres  are  distinguished  from  the  prece- 
ding by  the  absence  of  transverse  markings,  but  appear  to  be  tubular, 
their  contents  having  a  granular  existence,  without  any  definite  ar- 
rangement of  the  particles  into  disks  or  fibrillse.  Their  size  is  usually 
much  less  than  that  of  the  striated  muscular  fibre ;  but  owing  to  the 
extreme  variation  in  the  degree  of  fiattening  which  they  undergo,  it  is 
difficult  to  make  even  an  average  estimate  of  their  dimensions.  Those 
of  the  alimentary  canal  of  Man  are  stated  by  Dr.  Baly  to  measure 
from  about  the  l-2500th  to  the  l-5600th  part  of  an  inch  in  diameter. 


I 

u 

B 

M 

B 

1 

1 

W 

i 

■ 

1 

=■ 

§ 
B 

NON-STRIATED   MUSCULAR  FIBRE. 


201 


They  generally  present  nodosities  or  enlargements  at  frequent  intervals 
(Fig.  64) ;  the  character  of  which  will  be  presently  apparent.  These 
fibres  are,  like  those  of  the  other  muscles,  arranged  in  a  parallel 
manner  into  bands  or  fasciculi;  but  these  fasciculi  are  generally 
interwoven  into  a  network,  without  having  any  fixed  points  of  attach- 
ment. It  is  of  this  kind  of  structure,  that  the  proper  muscular  coat  of 
the  oesophagus,  of  the  stomach  and  intestinal  canal,  and  of  the  bladder, 
is  chiefly  composed.  It  has  been  recently  shown  by  Prof.  Kblliker, 
that  contractile  tissue  exists,  even  in  the  adult  state  of  the  highest 
animal,  under  its  very  simplest  form ;  that,  namely,  of  cells,  which  are 
usually  more  or  less  elongated.  These  are  composed  of  a  soft,  light 
yellow  substance,  which  swells  in  water  and  acetic  acid,  becoming  pale 
in  the  latter,  and  which  is  nearly  homogeneous,  so  that  it  is  difficult  to 
distinguish  the  cell-wall  clearly  from  the  cell-contents;  but  they  are 
jspecially  characterized  by  the  possession  of  long  staff-like  nuclei  (Fig. 


Fig.  64. 


Fig.  65. 


A.  A  muscular  fibre  of  organic  life 
from  the  urinary  bladder,  magni- 
fied 600  diameters.  Two  of  the  nu- 
clei are  seen. 

B.  A  muscular  fibre  of  organic 
life,  from  the  stomach,  magnified 
600  diameters.  The  diameter  of 
this  and  of  the  preceding  fibre, 
midway  between  the  nuclei,  was 
l-4750th  of  an  inch. 


Fusiform  contractile  cells : — a, 
trabecula  of  spleen,  with  the 
cells  in  situ;  B,  a  single  cell  iso- 
lated ;  c,  a  similar  cell  treated 
with  acetic  acid ; — a,  o,  cells  ;b,b, 
nuclei. 


65,  b,  b),  which  are  sometimes  only  rendered  perceptible  by  acetic  acid. 
These  cells  are  sometimes  so  little  elongated,  especially  in  the  walls  of 
the  blood-vessels,  that  they  might  be  taken  for  epithelium-cells ;  on  the 
other  hand,  they  frequently  pass  into  the  form  of  the  non-striated  fibres 
already  described.  They  are  very  commonly  fusiform  (Fig.  65,  b),  and 
are  then  arranged  in  the  manner  shown  in  Fig.  65,  A.  This  form  of 
muscular  structure  is  often  found  without  any  admixture  of  other  tissue, 
as  in  the  smaller  arteries,  veins,  and  lymphatics.  But  it  is  most  com- 
monly intermixed  with  the  various  forms  of  the  simple  fibrous  tissues ; 
and  in  this  state  it  is  found  in  the  circular  coat  of  the  larger  arteries 
and  veins,  in  the  erectile  tissues  generally,  in  the  skin,  and  especially 
the  dartos,  to  which  it  gives  a  contractility  that  is  manifested  under 
the  influence  of  cold  or  of  mental  emotions,  and  thus  produces  that 
general  roughness  and  rigidity  of  the  surface  which  is  known  as  cutis 
anserina,  whilst  it  throws  the  scrotum  into  wrinkles. 

338,  From  the  study  of  the  early  development  of  Muscular  Fibre,  it 


202 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 


appears  that  the  Myolemma,  or  external  transparent  tube,  is  the  part 
first  formed:  this  being  distinctly  visible,  long  before  any  traces  of 
fibrillse  can  be  observed  in  it.  This  tube  takes  its  origin,  like  the 
straight  ducts  of  Plants,  in  cells  laid  end  to  end ;  the  cavities  of  which 
coalesce,  by  the  disappearance  of  the  partitions,  at  a  subsequent  period. 
The  nuclei  of  these  original  cells  may  be  distinctly  seen,  for  some  time 
after  the  appearance  of  the  transverse  striae,  which  indicate  the  forma- 
tion of  the  fibrillae  in  their  interior ;  and  they  project  considerably  from 
the  sides  of  the  fibres.  In  the  fully-formed  muscle  of  animal  life,  how- 
ever, they  are  not  perceptible,  except  when  the  fibre  is  treated  with 
weak  acid ;  the  effect  of  which  is  to  render  the  nuclei  more  opaque, 
whilst  the  surrounding  structure  becomes  more  transparent  (Fig.  66). 


Mass  of  ultimate  fibres  from  the  pectoralis  major  of  the  human  foetus,  at  nine  months.  These  fibres 
have  been  immersed  in  a  solution  of  tartaric  acid,  and  their  "  numerous  corpuscles,  turned  in  various  direc- 
tions, some  presenting  nucleoli,"  are  shown. 

They  are  usually  numerous  in  proportion  to  the  size  of  the  fibre.  There 
is  every  probability  that  these  nuclei  continue  to  act,  like  the  "  germinal 
spots"  of  the  glandular  follicles,  as  centres  of  nutrition;  from  which  the 
minute  cells  that  compose  the  fibrillse  are  developed  as  they  are  required. 
The  diameter  of  the  Muscular  Fibre  of  the  foetus  is  not  above  one-third 
of  that  which  it  possesses  in  the  adult ;  and  as  the  size  of  the  ultimate 
particles  is  the  same  in  both  cases,  their  number  must  be  greatly  multi- 
plied during  the  growth  of  the  structure.  But  we  shall  find  reason  to 
believe,  that  the  decay  of  these  particles  is  constantly  taking  place, 
with  a  rapidity  proportional  to  the  functional  activity  of  the  Muscle ; 
and  their  generation,  which  occurs  as  continually,  when  the  nutrient 
operations  proceed  in  their  regular  course,  is  probably  accomplished  by 
a  development  from  these  centres,  at  the  expense  of  the  blood  with 
which  the  Muscle  is  copiously  supplied. 

339.  From  the  preceding  history  it  appears,  that  there  is  no  diffe- 
rence, at  an  early  stage  of  development,  between  the  striated  and  the 
non-striated  forms  of  muscular  fibre.  Both  are  simple  tubes,  containing 
a  granular  matter  in  which  no  definite  arrangement  can  be  traced,  and 
presenting  enlargements  occasioned  by  the  presence  of  the  nuclei.  But 
whilst  the  striated  fibre  goes  on  in  its  development,  until  the  fibrillae, 
with  their  alternation  of  light  and  dark  spaces,  are  fully  produced,  the 
non-striated  fibre  retains  throughout  life  its  original  embryonic  condi- 
tion.— And  it  may  further  be  remarked,  that  the  contractile  cells,  of 
which  many  of  the  non-striated  muscular  structures  are  composed,  are 
the  permanent  types  of  those  which  are  found  in  the  earliest  condition 


If 


11^ 


VESSELS   AND   NERVES   OF  MUSCLES.  203 

of  the  heart ;  whose  walls  are  composed  of  a  similar  tissue,  for  some 
time  after  its  rhythmical  movements  have  become  established. 

340.  We  have  seen  that  the  Muscular  tissue,  properly  so  called,  is 
,s  extra-vascular  as  cartilage  or  dentine  ;  for  its  fibres  are  not  pene- 
trated by  vessels  ;  and  the  nutriment  required  for  the  growth  of  its  con- 
tained matter  is  drawn  by  absorption  through  the  myolemma.  But  the 
substance  of  Muscle  is  extremely  vascular  ;  the  capillary  vessels  being 
distributed  in  nearly  parallel  lines,  in  the  minute  interspaces  between 
the  fibres  (Fig.  67) ;  so  that  it  is  probable  that  there  is  no  fibre,  which 

Fig.  67. 


Capillary  network  of  Muscle. 

is  not  in  close  relation  with  a  capillary.  Hence  there  is  every  provi- 
sion for  the  active  nutrition  of  this  tissue ;  the  arterial  circulation  bring- 
ing the  materials  for  its  growth  and  renovation ;  whilst  the  venous  con- 
veys away  the  products  of  the  waste  or  disintegration,  which  is  consequent 
upon  its  active  exercise. — The  supply  of  blood  is  not  merely  requisite 
for  the  nutrition  of  the  muscular  tissue ;  but  it  also  afibrds  a  condition 
which  is  requisite  for  its  action.  This  condition  is  oxygen.  It  is  not 
enough  that  blood  should  circulate  through  the  muscles  ;  for  that  blood, 
to  exercise  any  beneficial  influence,  must  be  arterialized.  Consequently 
the  muscles  of  warm-blooded  animals  soon  lose  their  contractile  power, 
after  the  supply  of  arterial  blood  has  been  suspended,  either  by  the  ces- 
sation of  the  circulation,  or  by  the  want  of  aeration  of  the  blood ;  but 
those  of  cold-blooded  animals  preserve  their  properties  for  a  much  longer 
period,  in  accordance  with  the  general  principle  formerly  stated, — that, 
the  lower  the  usual  amount  of  vital  energy,  the  longer  is  its  persistence, 
after  the  withdrawal  of  the  conditions  on  which  it  is  dependent. 

341.  The  Muscles  of  Animal  Life  are,  of  all  the  tissues  except  the 
Skin,  the  most  copiously  supplied  with  Nerves.  These,  like  the  blood- 
vessels, lie  on  the  outside  of  the  Myolemma  of  each  fibre ;  and  their 
influence  must  consequently  be  exerted  through'  it.  The  arrangement 
of  these  nerves  is  shown  in  the  succeeding  figure.  Their  ultimate  fibres 
or  tubes  cannot  be  said  to  terminate  anywhere  in  the  muscular  substance ; 
for  after  issuing  from  the  trunks,  they  form  a  series  of  loops,  which 
either  return  to  the  same  trunk,  or  join  an  adjacent  one  (Fig.  68).  The 
occasional  appearance  of  a  termination  to  a  nervous  fibril  is  usually 
caused  by  its  dipping  down  between  the  muscular  fibres,  to  pass  towards 
another  stratum  ;  but  it  appears  from  recent  inquiries  to  be  sometimes 
due  to  a  subdivision  of  the  central  axis  into  a  brush-like  group  of  minute 
fibrillge,  which. form  a  yet  minuter  plexus  around  the  muscular  fibres.-— 
The  non-striated  muscles,  however,  are  very  sparingly  supplied  with 


204 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 


nerves ;  and  these  are  derived  (for  the  most  part,  if  not  entirely)  from 
the  Sympathetic  system,  rather  than  from  the  Cerebro-spinal. 


Fig.  68. 

,iiiiaii!!3aii.miiiii!!iii.!mi,ci»faj<'i.i{\\-  _ 


-Vjr 


Portion  of  Muscle,  showing  tlie  arrangement  of  the  motor  nerves  supplying  it. 

842.  Every  Muscular  Fibre,  of  the  striated  kind  at  least,  is  attached 
at  its  extremities  to  fibrous  tissue ;  through  the  medium  of  which  it 
exerts  its  contractile  power  on  the  bone  or^ther  substance,  which  it  is 
destined  to  move.  The  muscular  fibre  usually  ends  abruptly  by  a  per- 
fect disk ;  and  the  myolemma  seems  to  terminate  there.  The  tendinous 
fibres  are  attached  to  the  whole  surface  of  the  disk  ;  and  seem  to  spread 
themselves  from  it  over  the  whole  myolemma.  Thus  the  whole  muscle 
is  penetrated  by  minute  fasciculi  of  tendinous  fibres ;  and  these  collect 
at  its  extremities  into  a  tendon.  Sometimes  the  muscular  fibres  are 
attached  obliquely  to  the  tendon,  which  forms  a  broad  band  that  does 
not  subdivide  ;  this  is  seen  in  the  legs  of  Insects  and  Crustacea,  in  which 
the  muscular  fibres  have  what  is  called  a  penniform  arrangement,  being 
inserted  into  the  tendon,  on  either  side,  like  the  laminae  of  a  feather 
into  its  stem.  The  forms  which  dijQTerent  muscles  present,  have  reference 
purely  to  the  mechanical  purposes,  which -they  have  respectively  to 
accomplish.  The  elements  are  the  same  in  all,  both  as  regards  structure 
and  properties. 

343.  Notwithstanding  the  energy  of  growth  in  Muscular  tissue,  it  is 
doubtful  if  it  is  ever  regenerated,  when  there  has  been  actual  loss  of 
substance.  Wounds  of  Muscles  are  united  by  Areolar  Tissue,  which 
gradually  becomes  condensed ;  but  its  fibres  never  acquire  any  degree 
of  contractility. 

344.  It  is  probable  that  the  pure  Muscular  Fibre  is  identical  in  ulti- 
mate composition,  or  nearly  so,  with  the  Fibrine  of  the  blood.  It  differs, 
however,  in  this :  that  the  fibrine  of  muscle  is  soluble  in  dilute  muriatic 
acid,  whilst  that  of  blood  swells  up  without  dissolving.  The  fibrine  of 
veal  bears  a  closer  resemblance  to  that  of  blood,  than  to  that  of  adult 
muscle.  In  ordinary  muscle,  the  solid  matter  forms  about  23  parts  in 
100 :  the  remainder  consisting  of  water.  The  solid  matter  contains 
about  7  J  per  cent  of  fixed  salts. 

345.  We  now  come  to  investigate  the  remarkable  property,  which  is 


CONTRACTILITY   OF   ORGANIZED  TISSUES.  205 

the  distinguishing  characteristic  of  Muscular  tissue ; — that  of  contract- 
ing on  the  application  of  a  stimulus.  Some  approaches  to  this  property- 
are  manifested  by  certain  Vegetable  structures.  Thus,  if  the  small 
enlargement  at  the  base  of  the  footstalk  of  the  leaf  of  the  Sensitive 
Plant  be  touched  ever  so  slightly,  the  leaf  will  be  immediately  drawn 
down  by  the  contraction  of  the  tissue  of  the  part  irritated.  If  the  leaf 
itself  be  touched,  the  same  effect  results,  but  apparently  through  a  diffe- 
rent channel ;  the  tissue  of  the  leaf  contracts  where  it  is  touched,  and 
forces  some  of  its  fluid  along  the  vessels  of  the  footstalk  into  the  upper 
side  of  the  little  excrescence  at  its  base,  by  the  distension  of  which  the 
leaf  is  forced  down.  In  the  Dionoea  museipula,  or  Yenus's  Fly-trap, 
there  is  a  similar  transmission  of  the  effect  of  the  stimulus  from  one 
part  to  another ;  for  the  two  lobes  of  the  leaf,  which  form  the  trap,  are 
made  to  close  together,  when  an  insect  settles  upon  either  one  of  three 
spines  which  project  from  the  surface  of  each  lobe,  or  when  the  points 
of  these  spines  are  touched  with  any  hard  body.  Many  other  instances 
of  Vegetable  movement  might  be  brought  together.  Some  of  them  are 
obviously  produced  by  an  enlargement  or  contraction  of  the  cells,  occa- 
sioned by  variations  in  the  amount  of  fluid  they  contain ;  and  these 
variations  depend  upon  the  hygrometric  state  of  the  atmosphere.  With 
these  we  have  nothing  to  do.  But  there  are  many,  in  which  (as  in 
the  case  of  the  Sensitive-plant  first  mentioned)  a  stimulus  applied  to  a 
part  occasions  the  immediate  contraction  of  its  cells,  and  a  consequent 
motion  in  the  same  part.  And  there  are  also  several,  in  which  the  con- 
traction produces  motion  in  a  distant  part,  as  in  the  Dionoea ;  but  this 
propagation  appears  to  be  of  a  simply  mechanical  character;  being 
accomplished  through  the  medium  of  fluid,  which  is  forced  from  one 
part  by  its  own  contraction,  and  caused  to  distend  another. 

346.  From  these  examples,  however,  it  is  evident  that  the  property 
of  contractility  is  not  entirely  restricted  to  the  Animal  kingdom ;  and 
we  shall  find  that  the  simplest  form  under  which  it  manifests  itself  in 
the  Animal  body,  bears  a  close  relationship  with  that  which  is  displayed 
in  Plants.  The  non-striated  fibre  of  the  alimentary  canal,  which  is  sub- 
servient to  the  functions  of  Vegetative  life  alone,  is  called  into  action 
much  more  readily  by  a  stimulus  directly  applied  to  itself,  than  it  is  in 
any  other  mode.  Such  is  not  the  case,  however,  with  the  striated  fibre, 
of  which  the  muscles  of  Animal  life  are  composed ;  this  being  much 
more  readily  called  into  action  by  a  peculiar  stimulus  conveyed  through 
the  nerves  supplying  those  muscles,  than  by  any  other  more  directly 
applied  to  them.  ^ 

347.  The  Contractility  of  Muscular  Fibre  shows  itself  under  two 
forms.  Its  most  obvious  and  striking  manifestations  are  those  that 
occur  in  the  voluntary  muscles  and  in  the  heart ;  which,  when  in  action, 
exhibit  powerful  contractions  alternating  with  relaxations.  The  property 
which  is  concerned  in  these  is  distinguished  as  Irritahility.  On  the 
other  hand,  we  find  that  these  same  muscles  exhibit  a  tendency  to  a 
moderate  and  permanent  contraction,  which  is  not  shown  by  them  when 
they  are  dead,  and  which  cannot  therefore  be  the  result  of  elasticity  or 
of  any  simple  physical  property ;  this  endowment,  which  seems  to  exist 


206  STRUCTURE  AND   ENDOWMENTS   OP  ANIMAL   TISSUES. 

in  the  greatest  amount  in  certain  forms  of  the  non-striated  fibre,  is  called 
Tonicity. 

848.  That  the  Irritability  of  Muscles  is  a  property  inherent  in  them, 
and  is  in  this  respect  analogous  to  the  peculiar  vital  endowments  of  any 
other  form  of  tissue,  cannot  be  any  longer  a  matter  of  doubt ;  though 
many  Physiologists  have  sought  to  show,  that  it  is  in  some  way  derived 
from  the  nerves.  Not  only  may  an  entire  Muscle  be  made  to  contract, 
by  the  application  of  a  proper  stimulus,  long  after  the  division  of  the 
nervous  trunks  supplying  it ;  but  even  a  single  fibre,  completely  isolated 
from  all  its  nervous  connexions,  may  be  seen  to  contract  under  the 
Microscope.  Moreover,  in  the  non-striated  muscular  fibre,  it  is  often 
difficult  to  excite  contractions  through  the  nerves  at  all,  when  a  stimulus 
directly  applied  to  itself  will  immediately  produce  sensible  and  vigorous 
movements.  The  energy  of  the  contractile  power  depends  in  great  part 
upon  the  state  of  nutrition  of  the  muscle  ;  and  this  again  is  influenced 
by  the  degree  in  which  it  is  exercised.  Nqw  as  the  Muscles  of  Animal 
Life  are  all  excited  to  action,  in  the  usual  state  of  things,  through  the 
medium  of  their  nerves,  it  follows  that  if  the  nerves  be  paralysed,  the 
muscles  will  be  seldom  or  never  called  into  use.  When  disused,  they 
will  receive  very  little  nourishment ;  the  disintegrating  changes  will  not 
be  counterbalanced  by  reparative  processes ;  and  in  consequence,  the 
muscular  structure  will  be  gradually  so  far  impaired,  as  to  lose  its  pecu- 
liar properties, — and  will  even,  in  time,  almost  totally  disappear.  Yet 
even  after  the  almost  complete  departure  of  muscular  contractility, 
through  the  metamorphosis  of  the  structure  consequent  upon  disuse,  it 
may  be  again  recovered,  if  the  muscles  be  called  into  exercise ;  but  the 
recovery  of  the  power  is  very  slow,  and  proceeds  'pari  passu  with  the 
improvement  in  the  nutrition  of  the  part,  being  more  tedious  in  propor- 
tion to  the  length  of  the  previous  disuse. 

349.  That  the  Irritability  of  Muscular  fibre  belongs  to  itself,  and  is 
not  derived  in  any  way  from  the  nerves,  is  further  shown  in  the  fol- 
lowing manner.  If  a  set  of  muscles  (as  those  of  the  leg  of  a  Rabbit 
or  Frog)  be  repeatedly  thrown  into  action  by  galvanism,  until  the 
stimulus  will  no  longer  occasion  their  contraction,  their  irritability  is 
then  said  to  be  exhausted ;  by  rest,  however,  it  is  recovered, — the  nu- 
tritive processes  making  good  the  loss  previously  suffered.  Now  it  has 
been  shown  by  Dr.  J.  Reid,  that  this  recovery  may  take  place,  even 
after  the  division  of  all  the  nerves  supplying  the  limb  ;  provided  that 
the  nutrition  of  the  part  be  not  interfered  with.  It  has  been  further 
shown  by  the  same  excellent  Physiologist,  that,  if  the  nerves  of  a  limb 
be  divided,  the  loss  or  retention  of  the  contractility  of  the  muscles  en- 
tirely depends  upon  the  degree  of  exercise  to  which  they  are  subjected, 
and  consequently  upon  the  nutrition  they  receive.  The  muscles  of  the 
hind-leg  of  a  Rabbit,  whose  sciatic  nerve  had  been  divided,  were  found 
to  lose  their  contractility  almost  completely  in  the  course  of  seven 
weeks.  They  were  much  smaller,  paler  and  softer,  than  the  corre- 
sponding muscles  of  the  opposite  leg ;  and  they  scarcely  weighed  more 
than  half  as  much  as  the  latter.  Now  when  the  nerves  of  both  hind- 
legs  of  a  Frog  were  cut,  and  the  muscles  of  one  of  the  limbs  thus 
paralysed  were  daily  exercised  by  a  weak  galvanic  battery,  while  those 


b> 


INHERENT   CONTRACTILITY   OP  MUSCULAR  FIBRE.  207 


of  the  other  were  allowed  to  remain  at  rest,  it  was  found  after  the 
lapse  of  two  months  that  the  muscles  of  the  exercised  limb  retained 
their  original  size  and  firmness,  and  contracted  vigorously,  whilst  those 
of  the  other  had  shrunk  to  one-half  their  former  size.  Though  the 
latter  still  retained  their  contractility,  there  could  be  no  doubt  that  they 
would  soon  lose  it,  in  consequence  of  the  change  already  far  advanced 
in  their  physical  structure  ;  this  change  not  being  as  rapid  in  cold-blooded 
animals,  as  in  Birds  and  Mammals. 

350.  By  these  and  other  facts,  then,  it  may  be  regarded,  as  com- 
pletely proved,  that  the  Irritability  of  Muscles  is  a  vital  endowment, 
belonging  to  them  in  virtue  of  their  peculiar  structure ; — that,  so  long 
as  this  structure  is  maintained  in  its  normal  condition  by  the  nutritive 
processes,  so  long  is  the  property  capable  of  being  manifested ; — but 
that  any  cause  which  interferes  with  the  nutrition  of  a  muscle,  impairs 
or  destroys  its  irritability.  No  cause  is  so  effectual  in  doing  this,  as 
complete  disuse;  and  no  means  is  so  sure  to  produce  complete  disuse 
of  a  muscle,  as  the  division  of  its  nerve,  since  its  being  called  into 
exercise  in  any  other  way  is  very  improbable ;  hence  the  section  of 
the  nerve  is  almost  certain  to  produce,  in  time,  the  loss  of  the  contrac- 
tility of  the  muscle.  But  if  a  means  be  devised,  by  which  the  muscle 
may  still  be "  called  into  action  in  any  other  way, — ^as  in  Dr.  Reid's 
experiment  just  quoted, — its  irritability  is  retained,  because  its  regular 
nutrition  is  continued. 

351.  We  have  now  to  inquire,  then,  into  the  circumstances  under 
which  this  peculiar  endowment  acts ;  or  the  means  by  which  it  may 
be  called  into  operation,  the  mode  in  which  the  contraction  takes  place, 
and  the  conditions  which  are  necessary  for  its  performance.  All  Mus- 
cular Fibre,  which  has  not  lost  its  contractility,  may  be  made  to  con- 
tract by  a  stimulus  applied  directly  to  itself ;  and  this  stimulus  may  be 
of  different  kinds.  The  simplest  is  the  contact  of  a  solid  substance ; 
thus  we  may  excite  muscular  contractions  by  simply  touching  the  fibre, 
just  as  we  cause  contraction  in  the  tissue  of  the  Dionsea  or  Sensitive 
Plant.  Most  substances  of  strong  chemical  action,  such  as  acids  and 
alkalies,  will  call  forth  the  contractility  of  muscular  fibre,  when  applied 
to  it ;  and  the  same  result  is  produced  by  heat,  cold,  and  electricity, — 
the  last-named  agent  being  the  most  powerful  of  all.  The  effect  of  the 
application  of  any  of  these  stimuli  varies  considerably,  according  to  the 
kind  of  Muscle  on  which  it  is  exerted.  If  we  irritate  a  portion  of  a 
muscle  composed  of  striated  fibre  (any  one  of  the  yoluntary  muscles,  for 
example),  the  fasciculus  of  fibres  which  is  touched  will  immediately 
contract,  and  that  one  only;  and  the  contracted  fasciculus  will  soon 
relax,  without  communicating  its  movement  to  any  other. 

352.  If  we  irritate  a  portion  of  non-striated  fibre,  however,  as  that 
of  the  Alimentary  canal,  the  fasciculus  which  is  stimulated  will  contract 
less  suddenly,  but  ultimately  to  a  greater  amount ;  its  relaxation  will 
be  less  speedy ;  and  before  it  takes  place,  other  fasciculi  in  the  neigh- 
bourhood begin  to  contract;  their  contraction  propagates  itself  to 
others ;  and  so  on.  In  this  manner,  successive  contractions  and  relax- 
ations may  be  produced  through  a  considerable  part  of  the  canal,  by  a 
single  prick  with  a  scalpel ;  a  sort  of  wave  of  contraction  being  trans- 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

mitted  in  the  direction  of  its  length,  and  being  followed  by  relaxation. 
Again,  in  the  Muscular  structure  of  the  Bladder  and  Uterus,  powerful 
contractions  are  excited  by  irritation,  and  these  produce  a  great  degree 
of  shortening :  but  they  do  not  alternate  in  the  healthy  state  with  any 
rapid  and  decided  elongation ;  whilst,  on  the  other  hand,  an  irritation 
applied  to  one  spot  causes  more  extensive  contractions,  than  are  seen  to 
occur  as  its  immediate  consequence  in  the  preceding  cases.  In  the 
Heart,  the  muscular  structure  of  a  large  part  of  the  organ  is  thrown 
into  rapid  and  energetic  contraction,  by  a  stimulus  applied  at  any  one 
point ;  and  this  contraction  is  speedily  followed  by  relaxation.  And 
in  the  fibrous  tissue  of  the  middle  coat  of  the  Arteries,  the  contraction 
takes  place  rather  after  the  manner  of  that  of  the  bladder  and  uterus, 
and  a  prolonged  application  of  the  stimulus  is  often  necessary  to  produce 
the  effect;  but  when  the  contraction  commences,  it  produces  a  consi- 
derable degree  of  shortening,  which  takes  place  in  other  fasciculi  than 
those  directly  irritated,  and  does  not  speedily  give  way  to  relaxation. 

353.  On  the  other  hand,  when  the  stimuli  which  excite  muscular 
contraction  are  applied  to  the  Nerve,  which  supplies  a  voluntary  muscle 
composed  of  striated  fibre,  they  produce  a  simultaneous  contraction  in 
the  whole  muscle ;  the  efiiect  of  the  stimulus  being  at  once  exerted 
upon  every  part  of  it.  In  the  ordinary  action  of  such  muscles,  the 
nervous  system  is  always  the  channel  through  which  they  are  called 
into  play,  whether  to  carry  into  effect  the  determinations  of  the  mind 
(§  391),  or  to  perform  ^ome  office  necessary  to  the  continuance  of  life, 
such  as  the  movements  concerned  in  Respiration  (§  394).  The  nerves 
of  the  striated  fibre  are  all  derived  at  once  from  the  brain  or  spinal 
cord.  The  ordinary  actions  of  the  non-striated  fibre,  on  the  contrary, 
are  executed  in  respondence  to  stimuli  applied  directly  to  themselves. 
It  is  so  difficult  to  excite  contractions  in  it  through  the  medium  of  its 
nerves,  that  many  Physiologists  have  denied  the  possibility  of  doing  so ; 
and  the  nerves  lose  their  power  of  conveying  the  influence  of  stimuli 
very  soon  after  death,  although  the  contractility  of  the  muscles  may 
remain  for  a  considerable  time.  The  nerves  of  the  non-striated  fibre 
are  chiefly  those  belonging  to  the  Sympathetic  system ;  but,  as  will  be 
shown  hereafter  (chap,  xii.),  those  which  excite  motion  are  probably 
derived  in  reality  from  the  Cerebro-spinal  system,  through  the  commu- 
nicating branches  which  unite  the  two. 

354.  When  a  Muscle  is  thrown  into  contraction,  its  bulk  does  not 
appear  to  be  at  all  affected.  Its  extremities  approach,  so  that  it  is 
shortened  in  the  direction  of  its  fibres ;  but  its  diameter  enlarges  in 
the  same  proportion.  It  was  formerly  supposed  that  the  ultimate 
fibres,  in  the  act  of  contraction,  threw  themselves  into  zigzag  folds ; 
but  this  is  now  well-ascertained  not  to  be  the  case.  The  fibre,  like 
the  entire  muscle,  preserves  its  straight  direction  in  shortening,  and 
increases  in  diameter.  The  fibrillse  themselves,  as  already  mentioned 
(§  336),  exhibit  an  evident  change,  in  regard  to  the  distances  of  their 
successive  light  and  dark  portions ;  and  the  fibre,  which  is  made  up  of 
these,  exhibits,  in  its  contracted  state,  a  very  close  approximation  of 
the  transverse  striae ;  to  such  an  extent  that  they  become  two,  three, 
or  even  four  times  as  numerous  in  a  given  length,  as  they  are  in  a 


Ii 


AGT    OF   MUSCULAR   CONTRACTION.  209 


similar  length  of  a  non-contracted  fibre.  According  to  Mr.  Bowman's 
observations,  the  contraction  usually  commences  at  the  extremities  of 
a  fibre;  but  it  may  occur  also  at  one  or  more  intermediate  points. 
The  first  appearance  of,  contraction  is  a  dark  spot,  caused  by  the  ap- 
proximation of  the  striae ;  and  this  gradually  extends  itself,  so  as  to 
involve  a  greater  or  less  proportion  of  the  length  of  the  fibre.  The 
approximation  of  the  solid  portions  forces  out  the  fluid,  which  was 
previously  contained  amongst  the  fibrillse;  and  this  is  seen  to  lie  in 
bullae  or  blebs  beneath  the  myolemma,  which  is  drawn  up  into  wrinkles. 

355.  The  successive  stages  of  the  act  of  contraction  can  only  be 
thus  observed,  when  it  takes  place  very  slowly,  as  in  the  rigor  mortis, 
or  slow  contraction  after  death,  the  phenomena  of  which  will  be  pre- 
sently noticed  (§  367).  But  the  resulting  change  in  muscular  fibres, 
which  haye  been  made  to  contract  by  galvanism  or  any  other  stimulus, 
is  essentially  the  same.  This  may  be  best  seen  in  transparent  Entozoa, 
Crustacea,  and  others  among  the  lower  Articulated  Animals,  whilst 
alive.  Again,  in  persons  who  have  died  from  Tetanus,  a  considerable 
number  of  the  fibres  are  found  to  have  been  ruptured  by  violent  spas- 
modic action  ;  the  contractile  force,  called  into  action  by  the  powerful 
stimulation  of  the  nerves,  having  overcome  the  tenacity  of  the  fibre: 
and  in  such  cases,  the  same  approximation  of  the  transveise  striae, 
and  proportional  increase  in  the  diameter  of  the  fibre,  are  to  be 
observed. 

356.  It  appears  that,  even  when  considerable  force  of  contraction  is 
being  exerted,  the  whole  fibre  is  seldom  or  never  in  contraction  at 
once;  but  that  a  continual  interchange  is  taking  place  amongst  its 
diff*erent  parts, — some  of  them  passing  from  the  contracted  to  the 
relaxed  state,  as  shown  by  the  separation  of  the  transverse  striae, — 
whilst  others  are  taking  up  the  duty,  and  passing  from  the  relaxed  to 
the  contracted  condition,  as  shown  by  the  approximation  of  the  striae. 
But  it  is  not  only  among  the  difi*erent  parts  of  the  individual  fibres, 
that  this  interchange  seems  to  take  place.  There  is  good  reason  to 
believe,  that,  when  a  muscle  is  kept  in  a  contracted  state,  by  an  effort 
of  the  will,  for  any  length  of  time,  only  a  part  of  its  fibres  are  in  con- 
traction at  any  one  time ;  but  that  a  constant  interchange  of  condition 
takes  place  amongst  them,  some  contracting  while  others  are  relaxing, 
so  that  the  entire  muscle  remains  contracted,  whilst  the  state  of  every 
individual  fibre  may  have  undergone  a  succession  of  alterations.  When 
the  ear  is  applied  to  a  muscle  in  vigorous  action,  an  exceedingly  rapid, 
faint,  silvery  vibration  is  heard,  which  seems  to  be  attributable  to  this 
constant  movement  in  its  substance. 

357.  Thus  it  appears  that  the  prolongation  of  the  contraction  of  a 
muscle,  through  any  length  of  time,  is  not  opposed  to  the  fact  that,  in 
the  individual  fibres,  relaxation  speedily  follows  contraction;  but  is 
only  a  peculiar  manifestation  of  it.  The  ordinary  movements  of  the 
Heart  exhibit  a  different  manifestation ;  its  fibres  contracting  simulta- 
neously, and  relaxing  together,  instead  of  alternating  amongst  them- 
selves like  those  of  a  voluntary  muscle.  The  occasional  zigzag  ar- 
rangement of  the  fibres,  which  has  been  supposed  to  be  their  contracted 
state,  is  really  dependent  upon  the  approximation  of  their  extremities, 


210  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

in  consequence  of  the  contraction  of  some  neighbouring  fibres,  whilst 
their  own  condition  is  that  of  relaxation.  It  may  be  artificially  pro- 
duced by  bringing  together  the  two  extremities  of  a  fasciculus,  after 
the  irritability  of  the  fibre  has  ceased ;  so  that  the  flexure  at  deter- 
minate points  must  be  owing  simply  to  the  physical  arrangement  of 
the  parts, — perhaps  to  the  passage  of  nerves  or  vessels  in  a  transverse 
direction. 

358.  We  have  now  to  consider  the  conditions  which  are  requisite  for 
the  manifestation  of  Muscular  Irritability.  It  has  been  already  pointed 
out,  how  close  is  the  dependence  of  the  property  upon  the  due  nutrition 
of  the  tissue ;  but  the  property  cannot  be  long  exercised  except  under 
another  condition,  which  is  consequently  of  almost  equal  importance, — 
the  circulation  of  arterial  blood  through  the  substance  of  the  muscle. 
The  length  of  time  during  which  the  contractility  remains,  after  the 
circulation  has  ceased,  has  been  shown  by  Dr.  M.  Hall  to  vary  inversely 
to  the  activity  of  the  respiration  of  the  animal.  In  coZc?-blooded  animals, 
the  standard  of  whose  respiration  is  low,  the  contractility  remains  for 
many  hours  after  death,  even  in  the  voluntary  muscles ;  and  the  muscles 
of  organic  life  retain  it  with  great  tenacity.  Thus  the  heart  of  a  Frog 
will  go  on  pulsating  for  many  hours  after  its  removal  from  the  body ; 
and  the  heart  of  a  Sturgeon,  which  had  been  inflated  with  air  and  hung 
up  to  dry,  has  been  seen  to  continue  beating,  until  the  auricle  had  be- 
come absolutely  so  dry  as  to  rustle  during  its  movements.  An  exceed- 
ingly feeble  Galvanic  current  is  sufficient  to  excite  the  muscles  of  these 
animals  to  contraction;  so  that  Matteucci,  in  his  experiments  upon 
Animal  Electricity,  has  been  accustomed  to  use  the  prepared  hind-leg 
of  a  Frog  as  the  best  indicator  of  the  passage  of  an  electric  current. 
Among  w^arw-blooded  animals,  whose  respiration  is  vastly  more  active, 
the  duration  of  the  irritability  is  proportionally  abbreviated;  and  the 
muscles  of  Birds,  whose  respiration  is  peculiarly  energetic,  lose  this 
property  at  an  earlier  period  after  the  cessation  of  the  circulation,  than 
do  those  of  Mammals.  From  experiments  on  the  bodies  of  executed 
criminals,  who  were  previously  in  good  health,  Nysten  ascertained  that, 
in  the  Human  subject,  the  contractility  of  the  several  muscular  struc- 
tures, as  tested  by  Galvanism,  departs  in  the  following  time  and  order : 
— the  left  ventricle  of  the  heart  first ;  the  intestinal  canal  at  the  end  of 
45  or  55  minutes ;  the  urinary  bladder  nearly  at  the  same  time ;  the 
right  ventricle  after  the  lapse  of  an  hour ;  the  oesophagus  at  the  expira- 
tion of  an  hour  and  a  half;  the  iris  a  quarter  of  an  hour  later ;  and  lastly, 
the  ventricles  of  the  heart,  especially  the  right,  which  in  one  instance 
contracted  16J  hours  after  death. 

359.  That  the  circulation  of  arterial  or  oxygenated  blood  through 
the  muscles,  is  the  essential  condition  of  the  continuance  of  their  irri- 
tability, appears  from  this, — that  after  the  general  death  of  the  system, 
and  even  after  the  removal  of  the  brain  and  spinal  cord,  the  muscles 
will  preserve  their  irritability,  and  the  action  of  the  heart  itself  will 
continue  for  a  long  time,  provided  that  the  circulation  be  kept  up 
through  the  lungs  by  artificial  respiration,  on  the  principles  hereafter 
to  be  explained  (§  688).  But  if,  whilst  the  general  circulation  con- 
tinues, the  circulation  through  a  particular  muscular  part  be  inter- 


I 


DEPENDENCE   OF   MUSCULAR   CONTRACTION   UPON   OXYGEN.        211 


rupted,  that  organ  will  lose  its  contractility  earlier  than  usual.  Thus 
it  has  been  shown  by  Mr.  Erichsen,  that,  if  the  coronary  arteries  (sup- 
plying the  substance  of  the  heart)  be  tied  in  a  dog  or  rabbit,  after  the 
animal  has  been  pithed,  and  the  circulation  is  being  maintained  by  arti- 
ficial respiration,  the  pulsation  of  the  heart  will  only  go  on  for  about  23 
minutes  after  the  ligature  has  been  applied,  or  about  33  minutes  after 
the  death  of  the  animal ;  instead  of  continuing  for  90  minutes,  which 
it  will  do  under  other  circumstances.  Further,  if  blood  charged  with 
carbonic  acid,  instead  of  with  oxygen,  circulate  through  the  muscles, 
their  irritability  is  speedily  impaired,  and  is  even  destroyed.  This  is 
best  seen,  when  animals  are  killed  by  being  caused  to  breathe  an  atmo- 
sphere highly  charged  with  carbonic  acid;  the  irritability  of  their 
muscles  departing  as  soon  as  they  are  dead.  In  fact,  the  destruction 
of  the  irritability  of  the  heart,  by  the  circulation  of  venous  blood  through 
its  substance,  is  one  of  the  immediate  causes  of  death.  A  similar  effect 
is  produced  by  the  respiration  of  other  gases,  which  are  either  poisonous 
in  themselves,  or  which  prevent  the  interchange  of  carbonic  acid  and 
oxygen,  which  ought  to  take  place  in  the  lungs.  On  the  other  hand, 
when  animals  have  been  made  to  respire  oxygen,  and  their  blood  has 
been  consequently  highly  arterialized,  the  contractility  of  their  muscles 
is  retained  for  a  longer  time  than  usual. 

360.  Hence  we  may  conclude  the  presence  of  oxygen  in  the  blood  to 
be  one  of  the  conditions  of  muscular  contraction  ;  although  it  is  much 
less  essential  in  the  case  of  cold-blooded,  than  in  that  of  warm-blooded 
animals.  It  is  interesting  to  remark,  that  the  muscles  of  hyhernating 
warm-blooded  Mammals  are  reduced  for  a  time  to  the  level  of  those  of 
cold-blooded  animals  ;  their  contractility  being  retained  almost  as  long 
as  that  of  the  latter ; — thus  confirming  the  general  principle  already 
stated,  as  to  the  relation  between  the  amount  of  respiration,  and  the 
duration  of  the  irritability. 

361.  The  Muscles,  as  we  have  seen,  are  largely  supplied  with  blood ; 
and  the  flow  of  blood  into  them  increases  with  the  use  that  is  made  of 
them.  The  demand  for  nutrition  is  obviously  augmented,  in  proportion 
to  the  activity  of  the  exercise  of  the  Muscular  system ;  for  the  slightest 
observation  sufiices  to  show,  that  a  much  smaller  amount  of  nourishment 
is  sufficient  to  sustain  the  body  in  its  normal  condition,  when  the  Mus- 
cular system  is  not  actively  exercised,  than  when  it  is  in  energetic 
operation.  The  quantity  which  is  ample  for  an  individual  leading  an 
inactive  life,  is  far  too  little  for  the  same  person  m  the  full  exercise  of 
his  muscular  power. — Again,  there  is  evidence  derive(J  from  observation 
of .  the  relative  amount  of  the  solid  matters  excreted  from  the  body 
under  different  circumstances  (§  731),  that  a  waste  or  disintegration  of 
the  muscular  tissue  takes  place,  whenever  it  is  actively  employed ;  and 
this  in  a  degree  strictly  proportional  to  the  amount  of  force  which  it  is 
called  upon  to  exercise.  In  fact,  it  would  appear  that  this  waste  is  a 
necessary  consequence  of  the  exercise  of  the  muscle  ;  every  act  of  con- 
traction involving  the  death  and  decomposition  of  a  certain  amount  of 
tissue.  And  as  the  presence  of  oxygen  is  always  necessary  for  the 
decomposition  of  organic  substances,  so  do  we  find  that  the  penetration 
of  the  muscular  tissue  by  oxygenated  blood  is  essential  to  the  manifes- 


212  STRUCTURE   AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

tation  of  its  contractile  power. — Every  act  of  contraction,  then,  may  be 
said  to  involve  the  death  of  a  certain  amount  of  muscular  tissue ;  and, 
on  the  principles  formerly  laid  down  (chap.  I.,  Sect.  3),  we  may  look 
upon  the  development  of  contractile  power  as  an  expenditure  of  the 
vital  force  which  that  tissue  previously  possessed,  and  which  ceases 
to  exist  as  such,  when  the  elements  of  the  tissue  enter  into  new 
combinations. 

362.  On  the  other  hand,  the  muscular  substance  is  repaired  by  an 
act  of  nutrition,  at  the  expense  of  the  fibrine  supplied  to  it  by  the 
circulating  fluid.  There  are  certain  muscles,  as  the  heart,  and  the 
muscles  of  respiration,  whose  action  is  necessarily  constant ;  and  their 
reparation  miist  take  place  as  unceasingly  as  their  waste.  In  these 
muscles,  no  sense  of  fatigue  is  ever  experienced.  But  in  the  muscles 
which  are  usually  put  in  action  by  the  will,  this  is  not  the  case.  Any 
prolonged  exertion  of  them  induces  fatigue  ;  and  this  fatigue  is  an  evi- 
dence of  their  impaired  condition,  and  of  the  necessity  of  rest  to  impart 
to  them  a  renewal  of  vigour.  The  rest  of  muscles  is  essential  to  the 
recovery  of  their  powers ;  and  this  recovery  is  due  to  the  nutritive 
operations,  which  then  take  place  unchecked,  and  which  repair  the 
losses  previously  sustained.  The  permanently-increased  flow  of  blood 
to  a  muscle,  which  takes  place  when  it  is  continually  being  called  into 
vigorous  action,  is  thus  on  the  one  hand  occasioned  by  the  demand  for 
oxygenated  blood  created  by  its  use,  whilst  on  the  other  hand  it  tends 
to  increase  the  power  of  the  muscle  by  an  augmentation  of  its  nutrition. 
Hence  it  is,  that,  the  more  a  muscle  is  exercised,  the  more  vigorous 
and  more  bulky  does  it  become.  This  is  equally  the  case,  whether 
the  exercise  of  the  muscle  be  voluntary  or  not.  We  see  examples  of 
it  in  the  arms  of  the  smith  and  in  the  legs  of  the  opera-dancer ;  and 
we  have  a  still  more  striking  manifestation  of  it  in  those  cases,  in 
which  an  obstruction  to  the  exit  of  urine  through  the  urethra,  has  called 
for  increased  efibrts  on  the  part  of  the  bladder,  the  continuance  of 
which  gives  rise  to  an  extraordinary  augmentation  in  the  thickness  of 
its  muscular  coat. 

363.  Thus  we  see  that  the  property  of  Irritability  is  a  vital  endow- 
ment peculiar  to  muscular  tissue,  and  dependent  for  its  existence  upon 
due  nutrition  of  that  tissue ;  that  it  may  be  called  into  exercise  by  cer- 
tain stimuli,  applied  either  to  the  muscle  itself,  or  to  the  nerve  supply- 
ing it,  provided  that  the  muscle  be  also  permeated  with  oxygen ;  that 
it  may  be  exhausj:ed  by  repeated  stimulation,  but  is  then  recovered  by 
rest,  provided  that  there  be  no  obstacle  to  the  nutrition  of  the  muscle ; 
that  the  nutrition  of  the  muscle  is  impaired  by  continued  repose,  and 
that  its  irritability  diminishes  in  the  same  proportion ;  that  the  nutri- 
tion is  increased  by  frequent  use,  and  that  the  power  of  the  muscle  then 
augments  in  like  degree ;  and  finally,  that  the  departure  of  muscular 
power,  which  ensues  upon  the  general  death  of  the  system,  is  depen- 
dent in  part  upon  the  cessation  of  the  supply  of  oxygen,  and  in  part 
tipon  changes  in  the  composition  of  the  muscle  itself,  which  are  no 
longer  compensated  by  the  functions  that  keep  it  in  its  normal  condition 
during  life.— The  rapidity  of  these  changes  is  the  greatest  in  warm- 
blooded animals,  in  which  also  the  muscular  irritability  is  most  depen- 


TONICITY   OF   MUSCLES. — RIGOR   MORTIS.  213 

dent  upon  the  presence  of  oxygen  in  the  muscular  substance ;  conse- 
quently the  irritability  departs  after  death  much  more  speedily  in  these 
than  in  cold-blooded  animals. 

364.  We  have  now  to  consider  the  other  form  of  Contractility ;  which 
produces  a  constant  tendency  to  contraction  in  the  Muscular  fibre,  but 
which  is  so  far  different  from  simple  Elasticity,  that  it  abates  after 
death,  before  decomposition  has  taken  place.  This  Tonicity  manifests 
itself  in  the  retraction  which  takes  place  in  the  ends  of  a  living  muscle, 
when  it  is  divided ;  the  retraction  being  permanent,  and  greater  than 
that  of  a  dead  muscle.  It  also  shows  itself  in  the  permanent  flexure 
of  joints,  when,  by  paralysis  of  the  extensors,  the  tonic  contraction  of 
the  flexors  is  not  antagonized.  In  the  healthy  state,  it  would  seem  as 
if  the  tonicity  of  the  several  groups  of  muscles  was  so  adjusted,  as  to  be 
in  mutual  counterpoise ;  but  the  balance  is  destroyed,  when,  in  conse- 
quence of  paralysis,  or  of  impaired  nutrition  from  other  causes,  the' 
tonicity  of  one  set  is  weakened.  This  is  the  case,  for  example,  in  the 
lead  palsy ;  in  which  the  extensors  of  the  forearm  and  hand  lose  their 
power,  so  that  the  tonic  contraction  of  the  flexors  keeps  the  fingers  con- 
stantly bent  upon  the  palm.  It  would  seem,  however,  that  the  tonicity 
of  the  flexors  is  usually  greater  than  that  of  the  extensors ;  as  the 
former  predominate,  when  all  are  equally  withdrawn  from  the  control  of 
the  nervous  system,  in  profound  sleep. 

365.  The  Tonicity  is  much  greater,  relatively  to  the  amount  of  irri- 
tability, in  the  non-striated,  than  in  the  striated  fibre ;  and  it  is  parti- 
cularly remarkable  in  the  fibrous  coat  of  the  arteries,  in  which  it  is 
difficult  to  procure  any  decided  indication-  of  irritability  by  the  applica- 
tion of  stimuli.  It  is  by  this  tonicity  of  the  walls  of  the  arteries,  that 
they  are  kept  in  a  state  of  constant  moderate  contraction  upon  their 
contents ;  and  that,  when  they  are  emptied,  they  contract  until  the 
tube  is  nearly  obliterated.  If  its  amount  be  too  great  (as  sometimes 
happens)  the  artery  approaches  the  condition  of  a  rigid  tube ;  which,  as 
will  be  shown  hereafter  (§  583),  is  unfavourable  to  the  regularity  of  the 
flow  of  blood  through  it,  though  the  rate  is  increased.  On  the  other 
hand,  if  it  be  unduly  diminished,  the  circulation  is  retarded,  by  the 
tendency  of  the  arterial  walls  to  yield  too  much  to  the  pulse-wave. 

366.  This  property  is  very  greatly  affected  by  temperature ;  being 
diminished  by  warmth  and  increased  by  cold.  Thus  when  an  artery 
is  exposed  to  the  air  for  some  time,  the  lowering  of  its  temperature 
occasions  its  contraction  to  such  an  extent,  that  its  tube  may  be  almost 
obliterated.  And  in  the  operation  of  crimping  ^fish,  immersion  of  the 
body  in  cold  water,  after  the  muscles  have  been  divided,  increases  the 
tonic  contraction  of  the  muscles,  and  thus  improves  the  firmness  of  their 
substance,  which  it  is  the  object  of  this  operation  to  produce. 

367.  The  Rigor  Mortis,  or  death-stiffening  of  the  muscles,  is  pro- 
bably to  be  regarded  as  a  manifestation  of  this  property,  occurring 
after  all  the  irritability  of  the  muscles  has  departed,  but  before  any 
putrefactive  change  has  commenced.  This  phenomenon  is  rarely  ab- 
sent ;  although  it  may  be  so  slight,  and  may  last  for  so  short  a  time,  as 
to  escape  observation.  The  period  which  elapses  before  its  commence- 
ment is  as  variable  as  its  duration ;  and  both  seem  to  be  dependent 


214  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

upon  the  vital  condition  of  the  system  at  the  time  of  death.  When  it 
has  been  weakened  or  depressed  by  previous  disease,  the  irritability  of 
the  muscles  speedily  departs ;  and  the  stiffening  comes  on  early,  and 
lasts  but  a  short  time.  Thus,  after  death  from  Typhus,  the  limbs  have 
been  sometimes  known  to  stiffen  within  15  or  20  minutes.  On  the  other 
hand,  when  the  general  vigour  of  the  system  has  not  been  previously 
impaired,  and  death  has  resulted  from  .some  sudden  cause,  the  irritability 
of  the  muscles  is  of  longer  duration,  and  their  stiffening  is  consequently 
deferred.  The  commencement  of  the  rigidity  usually  takes  place  within 
seven  hours  after  death ;  but  twenty  or  even  thirty  hours  may  elapse 
before  it  shows  itself.  Its  general  duration  is  from  twenty-four  to 
thirty-six  hours ;  but  it  may  pass  off  much  more  rapidly,  or  it  may  be 
prolonged  through  several  days.  It  affects  all  the  muscles  composed  of 
the  striated  fibre  with  nearly  the  same  intensity ;  except  that  the  flexors 
usually  contract  more  strongly  than  the  extensors  (as  in  sleep),  the 
fingers  being  closed  upon  the  palm,  the  hand  bending  on  the  fore-arm, 
and  the  lower  jaw  being  drawn  firmly  against  the  upper.  And  it  even 
manifests  itself  in  muscles  that  have  been  thrown  out  of  use  by  paralysis, 
provided  that  their  nutrition  has  not  been  seriously  impaired. 

368.  This  tonic  contraction,  however,  is  most  remarkably  manifested 
in  the  non-striated  fibre ;  and  especially  in  the  heart  and  blood-vessels. 
As  soon  as  the  muscular  walls  of  the  several  cavities  lose  their  irrita- 
bility, they  begin  to  contract  forcibly  upon  their  contents,  and  thus  be- 
come stiff  and  firm,  although  they  were  previously  flaccid.  In  this 
manner,  the  ventricles  of  the  heart,  which  are  the  first  parts  to  lose 
their  irritability,  become  rigid  and  contracted  within  an  hour  or  two 
after  death ;  and  usually  remain  in  that  state  for  ten  or  twelve  hours, 
sometimes  for  twenty-four  or  thirty-six,  then  again  becoming  relaxed 
and  flaccid.  This  rigid  contracted  state  of  the  heart,  in  which  the  walls 
are  thickened  and  the  cavities  diminished,  was  formerly  supposed  to  be 
a  result  of  disease,  and  was  termed  concentric  hypertrophy ;  but  it  is 
now  known  to  be  the  natural  condition  of  the  organ,  at  the  period  when 
the  rigor  mortis  occurs  in  it.  The  contraction  of  the  arterial  tubes  is 
so  great,  as  to  produce  for  the  time  a  great  diminution  in  their  calibre ; 
and  this  doubtless  contributes  to  the  passage  of  the  blood  from  the  arte- 
rial into  the  venous  system,  which  almost  invariably  takes  place  within 
a  few  hours  after  death.  The  arteries  then  enlarge  again,  and  become 
quite  flaccid,  their  tubes  being  emptied  of  the  previous  contents ;  and  it 
was  from  this  circumstance,  that  the  ancient  physiologists  were  led  to 
imagine  that  the  arteries  are  not  destined  to  carry  blood,  but  air. 

369.  As  soon  as  the  Rigor  Mortis  departs,  the  muscles  pass  into  a 
state^  of  decomposition ;  in  fact,  it  is  by  the  commencement  of  decom- 
position, that  the  cessation  of  this  vital  property  is  occasioned.  Thus 
we  may  regard  the  Rigor  IVJortis  as  the  last  act  of  the  Muscular  Con- 
tractility :  and  in  this  respect  it  corresponds  with  the  coagulation  of  the 
blood,  which  also  is  the  closing  act  of  its  life,  when  it  is  drawn  from  the 
living  body,  or  has  ceased  to  circulate  (§  184).  There  are,  indeed,  many 
remarkable  points  of  correspondence  between  the  two  phenomena;  which 
have  induced  some  physiologists  to  believe,  that  rigor  mortis  is  in  fact 
nothing  else  than  the  coagulation  of  the  blood  in  the  muscles.     It  has 


CONTRACTILE   FORCE   OF   MUSCLES.  215 

been  shown  by  Mr.  Bowman,  however,  that  the  stiffening  of  the  muscles 
after  death  is  due  to  the  permanent  contraction  of  their  component  fibres 
and  that  the  coagulation  of  the  blood  can  have  nothing  to  do  with  it. 
Nevertheless,  this  contraction  may  be  considered  as  being,  for  the  mus- 
cular fibre,  a  phenomenon  of  very  much  the  same  kind  as  the  coagula- 
tion of  the  fluid  fibrine  of  the  blood, — especially  resembling  the  subse- 
quent contraction  of  the  clot,  which  takes  place  gradually,  within  a  few 
hours  after  its  separation.  The  causes  which  prevent  the  coagulation 
of  the  blood  after  death  (§  187),  usually  prevent  also  this  last  manifes- 
tation of  the  tonicity  of  the  muscles  ;  their  vitality  being  completely  de- 
stroyed, like  that  of  the  blood,  by  sudden  and  powerful  shocks  operating 
on  the  nervous  system,  or  by  the  complete  exhaustion  consequent  upon 
violent  and  long-continued  exertion,  as  when  animals  are  run  to  death. 
And  again,  the  tonicity  of  muscles  survives  the  freezing  process ;  mani- 
festing itself  by  contraction  and  rigidity,  in  a  muscle  that  has  been 
frozen  immediately  after  death,  and  is  subseqently  thawed ;  just  as  the 
peculiar  properties  of  the  fibrine  of  the  blood  cause  its  coagulation  upon 
being  thawed,  if  it  have  been  frozen  immediately  upon  being  drawn 
from  the  vessels. 

370.  The  power  by  which  the  elements  of  Muscular  fibre  are  caused 
to  approach  one  another  in .  the  exercise  of  their  Contractility,  differs 
from  any  other  with  which  we  are  acquainted.  Its  complete  dependence 
upon  the  life  of  the  tissue  is  remarkably  shown  by  the  fact  (ascertained 
by  Valentin),  that,  after  the  cessation  of  the  irritability,  the  muscles 
tear  with  a  far  less  weight,  than  they  were  previously  able  to  draw,  when 
excited  by  galvanism ;  so  that  their  contractile  force  is  much  greater  than 
that,  which  the  simple  cohesiveness  of  the  tissue  can  sustain.  More- 
Over,  it  has  been  shown  by  the  experiments  of  Schwann,  that  the  con- 
tractile force  is  greatest,  when  the  muscle  is  most  extended ;  so  that, 
with  the  same  stimulus,  it  can  overcome  a  greater  resistance  by  its  con- 
traction, when  it  has  been  previously  stretched  to  its  full  length,  than  it 
can  when  it  has  been  already  in  part  shortened  by  the  exercise  of  its 
contractile  force.  The'power  diminishes  progressively  with  the  further 
shortening  of  the  muscle ;  until  at  last  no  further  contraction  can  be 
produced  by  any  stimulus,  the  extreme  limit  having  been  reached. 
Hence  it  seems  as  if  the  contractile  force  of  Muscles  differs  completely 
from  other  forms  of  Attraction,  as  those  of  Gravitation,  Electricity,  &c. ; 
since  it  is  the  universal  law  of  their  operation,  that  the  force  increases, 
in  proportion  to  the  decrease  between  the  squares  of  the  distances  be- 
tween the  attracting  bodies ;  whilst,  in  the  case  bf  muscle,  the  force  de- 
creases, in  proportion  as  the  distance  between  the  attracting  particles 
decreases.  But  it  is  to  be  remembered  that  the  law  of  attraction  just 
quoted  supposes  the  particles  to  be  quite  free  to  approach  one  another ; 
and  this  they  obviously  are  not  in  the  contraction  of  a  muscle,  since  the 
approach  cannot  take  place  without  a  change  of  place  between  the  solid 
and  fluid  elements  (§  354).  Hence  it  is  difficult,  if  not  impossible,^  to 
discover  the  law,  which  shall  truly  express  the  nature  of  the  attraction 
between  the  ultimate  particles  of  Muscle  at  different  distances ;  but  the 
law  discovered  by  Schwann  expresses  the  force  actually  developed,  at 
the  different  states  of  muscular  contraction. 


216  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 

371.  It  has  been  ascertained  by  the  researches  of  MM.  Becquerel  and 
Breschet,  that  the  temperature  of  a  muscle  rises,  when  it  is  thrown  into 
energetic  contraction.  The  increase  is  ordinarily  but  about  1°  Fahr. ; 
but  it  may  amount  to  twice  as  much,  if  the  muscle  be  kept  in  action  for 
some  time,  as  in  the  exercise  of  sawing.  Two  causes  may  be  assigned 
for  this  increase.  It  may  depend  upon  the  chemical  changes  which 
take  place  in  the  Muscle,  as  a  necessary  condition  of  the  production 
of  its  force  (§  361) ;  or  it  may  be  the  result  of  the  friction  taking 
place  between  different  parts,  during  the  constant  interchange  of  their 
actions  (§  356).  Perhaps  both  these  causes  concur  in  producing  the 
effect. 

372.  The  Nervous  System,  taken  as  a  whole,  is  the  instrument  of  all 
those  operations,  which  peculiarly  distinguish  the  Animal  from  the  Plant ; 
and  it  serves  many  additional  purposes,  connected  with  the  Organic  or 
Vegetative  functions,  which  the  peculiar  arrangements  of  the  Animal 
body  involve.  Wherever  a  distinct  Nervous  System  can  be  made  out 
(which  has  not  yet  been  found  possible  in  the  lowest  Animals),  it  con- 
sists of  two  very  different  forms  of  structure ;  the  presence  of  both  of 
which,  therefore,  is  essential  to  our  idea  of  it  as  a  whole.  We  observe, 
in  the  first  place,  that  it  is  formed  of  trunks,  which  are  distributed  to 
the  different  parts  of  the  body,  especially  to  the  muscles  and  to  the  sen- 
sory surfaces ;  and  of  the  ganglia,  which  sometimes  appear  merely  as 
knots  or  enlargements  on  these  trunks,  but  which  in  other  cases,  have 
rather  the  character  of  central  masses,  from  which  the  trunks  proceed. 
Now  it  is  easily  established  by  experiment,  that  the  active  powers  of 
the  nervous  system  reside  in  the  ganglia;  and  that  the  trunks  serve 
merely  as  conductors  of  the  influence,  which  is  to  be  propagated  towards 
or  from  them.  For  if  a  trunk  be  divided  in  any  part  of  its  course,  all 
the  parts  to  which  the  portion  thus  cut  off  from  the  ganglion  is  distri- 
buted, are  completely  paralysed ;  that  is,  no  impression  made  upon  them 
is  felt  as  a  sensation,  and  no  motion  can  be  excited  in  them  by  any  act 
of  the  mind.  Or  if  the  substance  of  the  ganglion  be  destroyed,  all  the 
parts,^  which  are  exclusively  supplied  by  nervous  trunks  proceeding 
from  it,  are  in  like  manner  paralysed.  But  if,  when  a  trunk  is  divided, 
the  portion  still  connected  with  the  ganglion  be  pinched,  or  otherwise  irri- 
tated, sensations  are  felt,  which  are  referred  to  the  points  supplied  by 
the  separated  portion  of  the  trunk ;  which  shows  that  the  part  remaining 
in  connexion  with  the  ganglion  is  still  capable  of  conveying  impressions, 
and  that  the  ganglion  itself  receives  these  impressions  and  makes  them 
felt  as  sensations.  On  the  other  hand,  if  the  separated  portion  of  the 
trunk  be  irritated,  motions  are  excited  in  the  muscles  which  it  supplies ; 
showing  that  it  is  still  capable  of  conveying  the  motor  influence,  though 
cut  off  from  the  usual  source  of  that  influence. 

373.  When  we  minutely,  examine  the  trunks  of  the  nerves,  we  find 
that  they  are  composed,  in  the  first  place,  of  a  Neurilemma  or  nerve- 
sheath,  consisting  of  areolar  tissue ;  the  ofiice  of  which  is  evidently  that 
of  protecting  the  nerve-tubes,  and  of  isolating  them  from  the  surround- 
ing structures,  at  the  same  time  that  it  allows  blood-vessels  to  pass  into 
the  interior  of  the  J:runk.  From  the  interior  of  the  neurilemma,  thin 
layers  of  areolar  tissue  pass  into  the  midst  of  the  enclosed  bundle  of 


'j 


STRUCTURE   OF  NERVOUS   FIBRES   AND   TRUNKS.  217 

nervous  fibres ;  separating  it  into  numerous  smaller  fasciculi,  which  are 
thus  bound  together  and  supplied  with  blood-vessels.  The  capillaries 
are  distributed  very  much  on  the  same  plan  as  those  of  Muscular  tissue 
(Fig.  66) ;  the  network  being  composed  of  straight  vessels,  which  run 
along  the  course  of  the  nerve,  between  the  nerve-tubes,  and  which  are 
connected  at  intervals  by  transverse  vessels.  When  the  neurilemma  has 
been  removed,  and  the  trunk  has  been  separated  into  its  component 
fasciculi,  we  may  still  further  subdivide  the  fasciculi  themselves  by 
careful  dissection,  until  we  arrive  at  the  ultimate  Nervous  Fibre,  which 
is  the  essential  element  of  the  structure.  Two  forms  of  this  fibre  exist 
in  the  nerves  of  higher  animals,  bearing  a  considerable  analogy  to  the 
two  forms  of  the  muscular  fibre ;  one  being  known  as  the  tubular ; 
whilst  the  other,  which  seems  to  be  in  a  state  of  less  complete  develop- 
ment, is  distinguished  as  the  gelatinous.  These  require  a  separate 
description. 

374.  The  Nervous  fibre,  in  its  most  complete  form,  is  distinctly  tubular. 
It  is  composed  externally  of  a  very  delicate  transparent  membrane, 
which  is  apparently  quite  homogeneous :  this  is  obviously  analogous  to 
the  myolemma  of  the  Muscular  fibre,  and  serves,  like  it,  to  isolate  the 
contained  substance  most  completely  from  surrounding  structures.  This 
membranous  tube  is  not  penetrated  by  blood-vessels,  nor  does  it  branch 
or  anastomose  with  others  ;  and  there  is  reason  to  believe  it  to  be  con- 
tinuous from  the  origin  to  the  termination  of  the  nervous  trunk.  Within 
yfche  tube  is  a  hollow  cylinder,  of  a  material  known  as  the  White  sub- 
mance  of  Schwann^  which  difi*ers  in  composition  and  refracting  power 
from  the  matter  that  occupies  the  centre  of  the  tube,  and  of  which  the 
outer  and  inner  boundaries  are  marked  out  by  two  distinct  lines.  And 
the  centre  or  axis  of  the  tube  is  occupied  by  a  transparent  substance, 
which  is  termed  the  axis-cylinder.  There  is  reason  to  believe  that  this  last 
is  the  essential  component  of  the  nervous  fibre ;  and  that  the  hollow 
cylinder  which  surrounds  it,  serves,  like  the  external  investment,  chiefly 
for  its  complete  isolation.  The  whole  of  the  matter  contained  in  the 
tubular  sheath  is  extremely  soft ;  yielding  to  very  slight  pressure.  The 
tubular  sheath  itself  varies  in  density  in  different  parts ;  being  stronger 
in  the  nervous  trunks,  than  in  the  substance  of  the  brain  and  spinal 
cord.  In  the  former,  it  is  not  difiicult  to  show,  that  the  regular  form 
of  the  nerve-tube  is  a  perfect  cylinder ;  though  a  little  disturbance  will 
cause  an  alteration  in  this, — a  small  excess  of  pressure  in  one  part 
forcing  the  contents  of  the  tube  towards  another,  where  they  are  more 
free  to  distend  it,  and  thus  producing  a  swelling.  The  greater  delicacy 
of  the  tubular  sheath  in  the  latter,  causes  this  result  to  take  place  with 
yet  more  readiness ;  so  that  a  very  little  manipulation,  exercised  upon 
the  fibres  of  the  brain  and  spinal  cord,  or  on  those  of  special  sense, 
occasions  them  to  assume  a  varicose  or  beaded  appearance,  which,  when 
first  observed  by  Ehrenberg,  was  thought  to  be  characteristic  of  them. 
When  the  fibres  of  these  parts,  however,  are  examined  without  any  such 
preparation,  they  are  found  to  be  as  cylindrical  as  the  others. — The 
diameter  of  the  tubuli  is  usually  between  l-2000th  and  l-4000th  of  an 
inch.  Sometimes,  however,  it  is  as  much  as  l-1500th ;  and  occasionally 
as  little  as  l-14,000th.     They  are  larger  in  the  nerve-trunks  than  in  the 


218  STRUCTURE  AND   ENDOWMENTS   OP  ANIMAL  TISSUES. 

brain ;  and  they  diminish  in  the  latter  as  they  approach  the  cortical 
substance.  The  fibres  of  the  nerves  of  special  sense  are  smaller  than 
the  average,  in  every  part  of  their  course. 

375.  The  gelatinous  fibres  cannot  be  shown  to  consist  of  the  same 
variety  of  parts  as  the  preceding ;  no  tubular  envelope  can  be  distin- 
guished ;  and  the  white  substance  of  Schwann  seems  wanting.  They 
are  flattened,  soft  and  homogeneous  in  their  appearance,  bearing  a  con- 
siderable resemblance  to  the  unstriped  Muscular  fibres ;  and,  like  them, 
they  contain  numerous  cell-nuclei,  which  are  arranged  with  tolerable 
regularity.  These  nuclei  are  brought  into  view  by  acetic  acid,  which 
dissolves  the  rest  of  the  fibre,  leaving  them  unchanged.  The  gelatinous 
fibres  are  usually  of  smaller  size  than  the  tubular,  their  diameter  ave- 
raging between  the  l-6000th  and  the  l-4000th  of  an  inch ;  and  they 
sometimes  show  a  disposition  to  split  into  very  delicate  fibrillae.  Being 
of  a  yellowish-gray  colour,  they  have  been  sometimes  distinguished  as 
the  gray  fibres.  These  two  classes  of  fibres  have  been  supposed  to  be 
essentially  distinct  in  character  and  ofiice ;  the  "tubular"  having  been 
regarded  as  ministering  to  the  Animal  functions  of  sensation  and 
motion  ;  and  the  "gelatinous"  as  connected  with  the  Organic  or  nutri- 
tive operations.  The  facts  which  will  be  presently  stated  (§  388) 
regarding  their  origin,  however,  as  well  as  their  joint  existence  in  almost 
every  nerve,  are  decidedly  adverse  to  this  view ;  and  we  shall  find  rea- 
son to  consider  them  as  difi'ering  chiefly  in  grade  of  development.  In 
fact  it  appears  that  the  very  same  fibre  may  be  "tubular"  in  one  part 
of  its  course,  and  "gelatinous"  in  another. 

376.  The  Nerve-fibres  appear  to  run  continuously,  from  one  extremity 
of  a  nervous  cord  to  the  other,  without  anything  like  union  or  anasto- 
mosis ;  each  ultimate  fibre  probably  having  its  distinct  ofiice,  which  it 
cannot  share  with  another.  The  fasciculi,  or  bundles  of  fibres,  however, 
occasionally  intermix  and  exchange  fibres  with  each  other ;  and  this 
interchange  may  take  place  among  either  the  fasciculi  of  the  same  trunk, 
or  among  those  of  different  trunks.  Its  object  is  evidently  to  diffuse 
among  the  different  branches  the  endowments  of  a  particular  set  of 
fibres.  Thus  we  shall  hereafter  see  that,  in  all  the  Spinal  Nerves  of 
Vertebrata,  one  set  of  roots  ministers  to  sensation,  and  another  to 
motion ;  the  sensory  fibres  are  'principally  distributed  to  the  skin,  and 
the  motor  fibres  to  the  muscles  ;  but  every  branch  contains  both  sensory 
and  motor  fibres,  which  are  brought  together  by  the  interlacement  of 
those  connected  with  both  sets  of  roots.  In  the  head,  we  have  some 
nervous  trunks  which  have  sensory  roots  alone ;  and  others  which  have 
motor  roots  only ;  these  in  like  manner  acquire  each  other's  functions 
in  some  degree  by  an  interchange  of  filaments, — the  sensory  trunk 
receiving  motor  fibres,  and  the  motor  trunk  receiving  sensory  fibres. 
An  interchange  of  this  kind,  upon  a  very  extensive  scale,  takes  place 
between  the  Cerebro-spinal  system,  whose  ganglionic  centres  are  the 
brain  and  spinal  cord,  and  the  Sympathetic  system,  whose  centres  con- 
sist of  a  number  of  scattered  ganglia.  The  former  sends  a  large  number 
of  fibres  into  the  latter,  by  the  twigs  of  communication  near  the  origins 
of  the  Spinal  nerves,  as  well  as  by  their  connecting  branches ;  whilst 


i 


COMMUNICATIONS   BETWEEN  NERVOUS  TRUNKS.  219 


the  latter  sends  a  smaller  number  of  fibres  into  the  former,  these  being 
chiefly  of  the  gelatinous  kind. 

377.  Sometimes  we  find  the  fasciculi  of  several  distinct  trunks  united 
into  an  extensive  plexus;  the  sole  object  of  which  appears  to  be,  to 
give  a  more  advantageous  distribution  to  fibres,  which  all  possess  corre- 
sponding endowments.  Thus  the  brachial  plexus  mixes  together  the 
fibres  arising  by  five  pairs  of  roots,  on  either  side,  from  the  spinal  cord ; 
and  sends  off  five  principal  trunks  to  supply  the  arm.  Now,  if  each  of 
these  trunks  had  arisen  by  itself,  from  a  distinct  segment  of  the  spinal 
cord,  so  that  the  parts  on  which  it  is  distributed  had  only  a  single  con- 
nexion with  the  nervous  centres,  they  woul4  have  been  much  more 
liable  to  paralysis  than  they  are.  By  means  of  the  plexus,  every  part 
is  supplied  with  fibres  arising  from  each  of  the  five  segments  of  the 
spinal  cord ;  and  the  functions  of  the  whole  must,  therefore,  be  sus- 
pended, before  complete  paralysis  of  any  part  could  occur  from  a  cause 
which  operates  above  the  plexus.  This  may  be  experimentally  shown 
on  the  Frog,  whose  crural  plexus,  is  formed  by  the  interlacement  of  the 
component  fasciculi  of  three  trunks  on  each  side ;  for  section  of  the 
roots  of  one  of  these  produces  little  effect  on  the  general  movements  of 
the  limb ;  and  even  when  two  are  divided,  there  is  no  paralysis  of  any 
of  its  actions,  all  being  weakened  in  nearly  an  equal  degree. — It  is  pro- 
bable, however,  that  (as  suggested  by  Dr.  Gull)  the  chief  use  of  this 
arrangement  is  to  bring  groups  of  muscles  into  relation  with  the  different 

i segments  of  the  cord,  in  such  a  mode  that  their  actions  may  be  combined 
And  harmonized.  We  shall  hereafter  (chap,  xii.)  find  reason  to  believe 
Ihat  the  will  does  not  at  once  act  through  the  nerves  upon  the  muscles ; 
Ibut  that  it  plays  (so  to  speak)  upon  the  spinal  cord,  each  segment  of 
which  has  its  own  particular  endowments,  and  ministers  to  a  particular 
set  of  movements.  And  thus,  the  greater  the  variety  of  movements 
-which  any  part  is  destined  to  perform,  the  more  complicated  will  be  the 
'  nervous  plexus  by  which  its  muscles  are  connected  with  the  centres  of 
motion. 

378.  The  second  primary  element  of  the  Nervous  System,  without 
which  the  fibrous  portion  would  seem  to  be  totally  inoperative,  is  com- 
posed of  nucleated  cells,  containing  a  finely  granular  substance,  and 
lying  somewhat  loosely  in  the  midst  of  a  minute  plexus  of  blood-vessels 
(Fig.  69,  a).  Their  normal  form  may  be  regarded  as  globular  (hence 
they  have  been  termed  nerve-  or  ganglion-globules) ;  but  this  is  liable  to 
alteration  from  the  compression  they  suffer,  so  that  they  may  become 
oval  or  polygonal.  The  most  remarkable  change  of  form,  however, 
which  they  undergo,  is  by  an  extension  into  one  or  more  long  processes, 

•giving  them  a  caudate  or  a  stellate  aspect  (b,  b).  These  processes  are 
composed  of  a  finely-granular  substance,  resembling  that  of  the  interior 
of  the  vesicle,  with  which  they  seem  to  be  distinctly  continuous ;  and  if 
traced  to  a  distance,  they  are  frequently  found  to  become  continuous 
with  the  axis-cylinders  of  the  nerve-tubes.  As  a  general  rule,  according 
to  Professor  Kolliker,  only  one  nerve-tube  is  connected  with  each 
ganglion-cell;  but  this  rule  is  not  without  its  exceptions,  especially 
among  the  lower  animals.  The  other  processes  seem  to  inosculate  with 
those  of  other  cells,  so  as  to  establish  a  direct  communication  between 


220 


STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL   TISSUES. 


them.  In  some  instances,  again,  the  ganglionic  cell  comes  into  relation 
with  the  fibre,  not  by  sending  out  a  prolongation  which  is  continuous 
with  it,  but  by  being  received  into  the  cavity  of  the  fibre  (so  to  speak), 
by  an  extension  of  the  tubular  wall  over  it.  In  other  cases,  moreover, 
the  fibres  merely  pass  around  and  amongst  the  ganglionic  cells,  without 
coming  into  direct  connexion  with  them ;  and  when  this  is  the  case,  the 
ganglionic  cells  retain  their  simply  globular  character. — Besides  the 
finely  granular  substance  just,  mentioned,  these  cells  usually  contain  a 
collection  of  pigment  granules,  which  give  them  a  reddish  or  yellowish- 
brown  colour :  this,  however,  is  frequently  absent,  especially  among  the 
lower  animals. — The  size  of  the  vesicles  is  liable  to  great  variation  ;  the 
globular  ones  are  usually  between  l-300th  and  l-1250th  of  an  inch  in 
diameter. 

Fig.  69. 


Primitive  fibres  and  ganglionic  globules  of  human  brain,  after  Purkinjc.  A,  ganglionic -globules  lying 
amongst  varicose  nerve-tubes,  and  blood-vessels,  in  substance  of  optic  thalamus ;  a,  globule  more  enlarged; 
0,  small  vascular  trunk,  b,  b,  globules  with  variously-formed  peduncles,  from  dark  portion  of  crus  cerebri. 
350  Diam. 

379.  The  vesicles  just  described  are  aggregated  together  in  masses  of 
variable  size ;  and  are  in  some  degree  held  together  by  the  plexus  of 
blood-vessels  (Fig.  70),  in  the  midst  of  which  they  lie.  They  are  sometimes 
imbedded  in  a  soft  granular  substance,  which  adheres  closely  to  their 
exterior  and  to  their  processes ;  this  is  the  case  in  the  outer  part  of  the 
cortical  substance  of  the  human  brain.  In  other  instances,  each  cell  is 
enclosed  in  a  distinct  envelope,  composed  of  smaller  cells,  closely  adhe- 
rent to  each  other  and  to  the  contained  cell ;  such  an  arrangement  is 
common  in  the  smaller  ganglia,  and  in  the  inner  portion  of  the  cortical* 
substance  of  the  brain.  The  substance  which  is  made  up  of  these  pecu- 
liar cells,  of  the  plexus  of  the  blood-vessels  in  which  they  lie,  and  of  the 
granular  matter  that  is  disposed  amongst  them,  is  altogether  commonly 
known  as  the  cineritious  or  gray  substance ;  being  distinguished  by  its 
colour,  in  Man  and  the  higher  animals  at  least,  from  the  white  substance 
(composed  of  nerve-tubes)  of  which  the  trunks  of  the  nerves,  as  well  as 
a  large  part  of  the  brain  and  spinal  cord,  are  made  up.  But  this  dis- 
tinction is  by  no  means  constant ;  for  the  gray  colour,  which  is  partly 


r 


STRUCTURE  OF  NERVOUS  GANGLIA. 


221 


due  to  the  pigment-granules  of  the  cells,  and  partly  to  the  redness  of 
the  blood  in  the  vessels,  is  wanting  in  the  Invertebrata  generally,  and  is 
not  characteristically  seen  in  the  classes  of  Fishes  and  Reptiles.  More- 
over, when  the  ganglionic  substance  exists  in  small  amount,  even  in 


Capillary  network  of  Nervous  Centres. 

Man,  its  colour  is  not  sufficiently  intense  to  serve  to  distinguish  it ;  and, 
as  we  have  already  seen,  there  are  nerve-fibres  which  possess  a  grayish 
hue.  The  real  distinction  evidently  lies  in  the  form  of  the  ultimate 
structure,  which  is  fibrous  in  the  one  case,  and  cellular  or  vesicular  in 
the  other ;  and  these  terms  will  be  henceforth  used  to  characterize  the 
two  kinds  of  nervous  tissue,  which  have  been  now  described. 

380.  A  ganglion,  then,  essentially  consists  of  a  collection  of  nerve- 
vesicles  or  ganglion-globules,  interspersed  among  the  nerve-fibres  ;  and 
it  is  in  the  presence  of  the  former  that  it  differs  from  a  plexus,  which 
it  frequently  resembles  in  the  arrangement  of  the  latter.  When  a 
nerve  enters  a  ganglion,  its  component  fibres  separate  and  pass  through 
the  ganglion  in  different  directions,  so  as  to  be  variously  distributed 
among  the  branches  which  pass  out  of  it  (Fig.  71);  coming,  in  their 

Fig.  71. 


Dorsal  ganglion  of  Sympathetic  nerve  of  Mouse  ;—a,  b,  cords  of  connexion  with  adjacent  sympattietic 
ganglia;  c,  c,  c,  c,  branches  to  the  viscera  and  spinal  nerve ;  d,  ganglionic  globules  or  cells  ;  e,  nervous  fibres 
crossing  the  ganglion. 

course,  into  relation  with  the  vesicular  matter,  which  occupies  the  inte- 
rior of  the  ganglion,  in  one  or  more  of  the  modes  already  specified 
(§  378).     Some  of  the  fibres  may  terminate  in  the  cells  of  the  ganglion, 


222 


STRUCTURE  AND   ENDOWMENTS  OF  ANIMAL  TISSUES. 


and  new  ones  may  originate  in  them ;  so  that  there  is  no  constant  cor- 
respondence between  the  number  of  fibres  which  enter  a  ganglion,  and 
of  those  which  pass  out  of  it. — The  only  exception  to  the  general  fact, 
that  the  vesicular  matter  occupies  the  centre  of  the  ganglia,  occurs  in 
the  brain  of  Vertebrata,  in  which  it  is  chiefly  disposed  on  the  exterior, 
forming  the  cortical  envelope.  The  reason  for  this  variation  is  probably 
to  be  found  in  the  very  large  amount  of  this  substance,  which  the  brain 
of  the  higher  Vertebrata  contains ;  and  in  the  necessity  of  the  free 
access  of  blood-vessels  to  it,  which  is  provided  for  by  a  great  extension 
of  its  surface  beneath  the  investing  vascular  membrane  (pia  mater), 
more  readily  than  it  could  be  in  any  other  mode. 

381.  But  the  vesicular  matter  is  not  found  in  the  central  masses  only 
of  the  Nervous  system ;  for  it  presents  itself  also  at  those  parts  of  the 
surface  or  periphery  which  are  peculiarly  destined  to  receive  the  im- 
pressions that  are  to  be  conveyed  to  the  central  organs.  Thus  on  the 
expansion  of  the  optic  nerve  which  forms  the  retina,  there  is  a  distinct 
layer  of  ganglionic  corpuscles  or  nerve- cells,  with  a  minute  plexus  of 
vessels,  possessing  all  the  essential  characters  of  the  vesicular  substance 
of  the  brain;  and  something  of  the  same  kind  has  been  seen  in  con- 
nexion with  the  corresponding  expansion  of  the  olfactive  and  auditory 
nerves.  Moreover,  the  study  of  the  history  of  the  development  of  these 
organs  has  shown  that  the  vesicular  matter  of  the  retina  is  an  offshoot 
(so  to  speak)  from  that  of  the  optic  ganglion,  that  of  the  labyrinth  of 
the  ear  being  in  like  manner  an  offshoot  from  that  of  the  auditory  gan- 
glion. Thus  it  is  obvious  that  the  fibres  of  the  connecting  nerve  are 
interposed  between  the  cells  of  the  peripheral  and  those  of  the  central 
organs,  for  the  sake  of  preserving  that  connexion  between  them  which 
would  otherwise  have  been  interrupted ;  and  that  the  vesicular  matter 
is  the  active  agent  in  the  origination  of  those  changes  which  take  place 
as  a  consequence  of  sensory  impressions,  whilst  for  the  conduction  of 
such  changes,  the  fibrous  structure  is  alone  required. 

382.  The  ultimate  distribution  of  the  nerve-fibres  in  the  skin  and 
tongue,  however,  has  not  been  so  clearly  made  out,  nor  can  their  rela- 
tion to  cells  be  distinctly  traced.  These  fibres  are  distributed,  for  the 
most  part,  to  the  papillae,  in  which  they  can  be  frequently  seen  to  form 


Fig.  72. 


Fig.  73. 


Capillary  network  at  margin  of  lips. 


Difltribntion  of  the  tactile  nerves  at  the  snrfiuse  of  the 
lip ;  as  seen  in  a  thin  perpendicular  section  of  the  skin. 


loops  (Fig.  72),  accompanied  by  similar  loops  of  blood-vessels  (Fig.  73); 
but  no  such  loops  can  be  seen  in  the  fungiform  papillae  of  the  tongue, 


CHEMICAL   COMPOSITION   OP  NERVOUS  MATTER.  223 

the  continuity  of  whose  nerve-fibres  cannot  be  distinguished  near  their 
apices.  Here,  however,  the  history  of  the  development  of  the  nervous 
plexuses  in  the  skin  seems  to  show,  that  the  fibres  may  be  considered  as 
commencing  in  a  peripheral  ganglionic  expansion ;  for  it  has  been  shown 
by  the  observations  of  Prof.  Kblliker  upon  the  tail  of  the  tadpole,  that 
the  nervous  plexuses  are  formed  in  the  same  manner  as  the  capillary 
netwrok ;  namely,  by  the  inosculation  of  the  prolongations  of  radiating 
cells,  whose  centres  are  at  a  considerable  distance  from  each  other. 
Hence  it  is  probable  that  cell-nuclei,  or  some  equivalent  centres  of  force, 
remain  in  connexion  with  the  peripheral  nerve-fibres  of  the  skin  and 
tongue,  as  with  those  of  other  sensory  surfaces.  Sometimes  the  ultimate 
plexuses  seem  to  be  formed  in  the  Skin,  as  in  Muscle,  by  the  subdivision 
of  the  primitive  fibres  (§  341). 

383.  We  have  now  to  speak  briefly  of  the  Chemical  Composition  of 
the  Nervous  matter ; — a  consideration  which  will  be  presently  shown  to 
be  of  much  importance.  As  formerly  remarked  (§  7),  the  vital  activity 
of  a  tissue  is  usually  greater,  as  the  proportion  of  its  solid  to  its  fluid 
contents  is  less  ;  and  this  rule  holds  good  most  strikingly  in  regard  to 
the  Nervous  substance,  the  vital  activity  of  which  is  far  greater  than 
that  of  any  other  tissue,  and  the  solid  matter  of  which  usually  consti- 
tutes no  more  than  a  fourth,  and  occasionally  does  not  exceed  an  eighth 
of  its  entire  weight.  The  proportion  of  water  is  greatest  in  infancy  and 
least  in  middle  life ;  and  it  has  been  observed  to  be  under  the  average 
in  idiots.  Of  the  solid  matter  of  the  brain,  about  a  third  consists  of 
fibrine  or  albumen ;  which  is  probably  the  material  of  the  membrane  of 
the  tubuli,  as  well  as  of  the  tissue  that  connects  them. — It  is  chiefly  with 
the  Fatty  matter,  which  constitutes  about  a  third  of  the  solid  substance, 
that  the  attention  of  Chemists  has  been  occupied.  This  is  stated  by  M. 
Fremy  (one  of  the  most  recent  analysts)  to  contain,  besides  the  ordinary 
fatty  matters,  and  Cholesterine  or  biliary  fat,  two  peculiar  fatty  acids, 
termed  the  Cerebric  and  the  Oleo-phosphoric.  Qerehric  acid,  when  puri- 
fied, is  white,  and  presents  itself  in  crystalline  grains.  It  ^  contains  a 
small  proportion  of  Phosphorus ;  and  difi'ers  from  the  ordinary  fatty 
matters  in  containing  Nitrogen,  as  also  in  containing  twice  their  propor- 
tion of  oxygen.  Oleo-phosphoric  acid  is  separated  from  the  former  by 
its  solubility  in  ether ;  it  is  of  a  viscid  consistence ;  but  when  boiled  for 
a  long  time  in  water  or  alcohol,  it  gradually  loses  its  viscidity,  and  re- 
solves itself  into  a  pure  oil,  which  is  elaine,  while  phosphoric  acid  re- 
mains in  the  liquor.  The  proportion  of  phosphorus  in  the  brain  is  con- 
siderable ;  being  from  8  to  18  parts  in  1000  of  the  whole  mass,  or  from 
l-20th  to  l-30th  of  the  whole  solid  matter.  It  seems  to  be  unusually 
deficient  in  the  brain  of  idiots.  The  remaining  third  and  sometimes 
more,  is  composed  of  a  substance  termed  Osmazome  (which  seems  to  be 
a  proteine-compound  in  a  state  of  decomposition),  together  with  saline 
matter.  No  satisfactory  examination  has  yet  been  made  into  the  com- 
parative composition  of  the  vesicular  and  fibrous  substances ;  but  accord- 
ing to  Lassaigne,  the  former  contains  much  more  water  than  the  latter, 
and  little  colourless  fat,  but  nearly  4  per  cent,  of  red  fat,  which  does 
not  exist  in  the  other. 

384.  Various  circumstances  lead  to  the  belief,  that  the  Nervous  tissue. 


224  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

during  the  whole  period  of  active  life,  is  continually  undergoing  changes 
in  its  substance,  bj  decay  and  renewal.  We  know  that,  after  death,  it 
is  one  of  the  first  of  all  the  animal  tissues  to  exhibit  signs  of  decompo- 
sition ;  and  there  is  no  reason  to  suppose,  that  this  tendency  is  absent 
during  life.  Hence  for  the  simple  maintenance  of  its  normal  character, 
a  considerable  amount  of  nutritive  change  must  be  required.  But  many 
circumstances  further  lead  to  the  conclusion,  that,  like  all  other  tissues 
activelv  concerned  in  the  vital  operations.  Nervous  matter  is  subject 
to.  a  waste  or  disintegration,  which  bears  an  exact  proportion  to  the 
activity  of  its  operations  ; — or,  in  other  words,  that  every  act  of  the 
Nervous  system  involves  the  death  and  decay  of  a  certain  amount  of 
Nervous  matter,  the  replacement  of  which  will  be  requisite  in  order  to 
maintain  the  system  in  a  state  fit  for  action.  We  shall  hereafter  see, 
that  there  are  certain  parts  of  the  Nervous  system,  particularly  such  as 
put  in  action  the  respiratory  muscles,  which  are  in  a  state  of  unceasing, 
though  moderate,  activity ;  and  in  these,  the  constant  nutrition  is  suffi- 
cient to  repair  the  efiiects  of  the  constant  decay.  But  those  parts,  which 
operate  in  a  more  powerful  and  energetic  manner,  and  which  therefore 
waste  more  rapidly  when  in  action,  need  a  season  of  rest  for  their  repa- 
ration. Thus  a  sense  of  fatigue  is  experienced,  when  the  mind  has  been 
long  acting  through  its  instrument — the  brain  ;  indicating  the  necessity 
for  rest  and  reparation.  But  when  sleep,  or  cessation  of  the  cerebral 
functions,  comes  on,  the  process  of  nutrition  takes  place  with  unchecked 
energy,  counterbalances  the  results  of  the  previous  waste,  and  prepares 
the  organ  for  a  renewal  of  its  activity.  In  the  healthy  state  of  the 
body,  when  the  exertion  of  the  nervous  system  by  day  does  not  exceed 
that,  which  the  repose  of  the  night  may  compensate,  it  is  maintained  in 
a  condition  which  fits  it  for  constant  moderate  exercise ;  but  unusual 
demands  upon  its  powers, — whether  by  the  long-continued  and  severe 
exercise  of  the  intellect,  by  excitement  of  the  emotions,  or  by  the  com- 
bination of  both  in  that  state  of  anxiety  which  the  circumstances  of 
man's  condition  too  frequently  induce, — occasion  an  unusual  waste, 
which  requires,  for  the  complete  restoration  of  its  powers,  a  prolonged 
repose. 

385.  There  can  be  no  doubt  that  (from  causes  which  are  not  known), 
the  amount  pf  sleep  required  by  different  persons,  for  the  maintenance 
of  a  healthy  condition  of  the  nervous  system,  varies  considerably;  some 
being  able  to  dispense  with  it,  to  a  degree  which  would  be  exceedingly 
injurious  to  others  of  no  greater  mental  activity.  Where  a  prolonged 
exertion  of  the  mind  has  been  made,  and  the  natural  tendency  to  sleep 
has  been  habitually  resisted,  by  a  strong  effort  of  the  will,  injurious 
results  are  sure  to  follow.  The  bodily  health  breaks  down,  and  too 
frequently  the  mind  itself  is  permanently  enfeebled.  It  is  obvious  that 
the  nutrition  of  the  Nervous  system  becomes  completely  deranged ;  and 
that  the  tissue  is  no  longer  formed,  in  the  manner  requisite  for  the  dis- 
charge of  its  healthy  functions. 

386.  As  the  amount  of  Muscular  tissue  that  has  undergone  disinte- 
gration, is  represented  (other  things  being  equal),  by  the  quantity  of 
urea  in  the  urine,  so  do  we  find  that  an  unusual  waste  of  the  nervous 
matter  is  indicated  by  an  increase  in  the  amount  of  'phosphatic  deposits. 


WASTE  AND   RENEWAL   OF   NERVOUS  SUBSTANCE.  225 

No  others  of  the  soft  tissues  contain  any  large  proportion  of  phospho- 
rus ;  and  the  marked  increase  in  these  deposits,  which  has  been  con- 
tinually observed  to  accompany  long-continued  wear  of  mind,  whether 
by  intellectual  exertion,  or  by  anxiety,  can  scarcely  be  set  down  to  any 
other  cause.  The  most  satisfactory  proof  is  to  be  found  in  cases,  in 
which  there  is  a  periodical  demand  upon  the  mental  powers ;  as,  for 
example,  among  clergymen,  in  the  preparation  for,  and  discharge  of, 
their  Sunday  duties.  This  is  found  to  be  almost  invariably  followed 
by  the  appearance  of  a  large  quantity  of  the  phosphates  in  the  urine. 
And  in  cases,  in  which  constant  and  severe  intellectual  exertion  has 
impaired  the  nutrition  of  the  brain,  and  has  consequently  weakened 
the  mental  power,  it  is  found  that  any  premature  attempt  to  renew  the 
activity  of  its  exercise,  causes  the  reappearance  of  the  excessive  phos- 
phatic  discharge,  which  indicates  an  undue  waste  of  nervous  matter. 

387.  As  the  disintegration  of  the  Nervous  System  is  thus  propor- 
tional to  its  exercise,  so  must  its  reparation  make  a  corresponding  de- 
mand upon  the  nutritive  processes.  And  accordingly  we  find,  that  it 
is  very  copiously  supplied  with  blood-vessels ;  and  that  the  amount  of 
food,  appropriated  to  its  maintenance  in  an  active  condition,  is  very 
considerable.  This  we  know  from  the  fact,  that  persons  of  active  minds, 
but  sedentary  bodily  habits,  commonly  require  nearly  as  much  food  as 
those,  in  whom  the  waste  of  the  Muscular  system  is  greater,  and  that 
of  the  Nervous  system  less,  in  virtue  of  their  bodily  activity  and  the 
less  energetic  operation  of  their  minds. 

388.  The  nerve-fibres  appear  to  originate,  according  to  the  observa- 
tions of  Prof.  Kolliker,  in  cells  which  become  fusiform  by  elongation 
(§  193),  and  which  then  coalesce  at  their  extremities ;  and  these  seem 
to  increase,  after  the  first  formation  of  the  trunks,  by  the  longitu- 
dinal subdivision  of  fusiform  cells  which  had  not  previously  undergone 
complete  metamorphosis  into  fibres,  as  well  as  by  the  development  of 
cells  de  novo.  The  nuclei  of  the  original  cells  may  be  frequently  seen 
in  the  nerve-tubes  at  a  later  period,  lying  between  their  membranous 
walls  and  the  substance  deposited  in  their  interior.  The  earliest  condi- 
tion of  both  forms  of  nerve-fibre  appears  to  be  precisely  the  same  ;  but 
the  gelatinous  remains  in  a  state  nearly  resembling  this ;  whilst  the 
tubular  is  developed  into  a  higher  form.  Various  gradations,  indeed, 
may  be  traced  between  the  two.  The  vesicular  matter  appears  to  be  in 
a  state  of  continual  change,  as  is  the  case  with  all  cells  whose  functions 
are  active.  The  appearances  observed  by  Henle^  in  the  cortical  sub- 
stance of  the  brain  lead  to  the  belief,  that  there  is  as  continual  a  suc- 
cession of  nerve-cells,  as  there  is  of  epidermic  cells  ;  their  development 
commencing  at  the  surface,  where  they  are  most  copiously  supplied  with 
blood-vessels  from  the  investing  membrane,  and  proceeding  as  they  are 
carried  towards  the  inner  layers,  where  they  oome  into  more  immediate 
relation  with  the  fibrous  portion  of  the  nerve-structure.  This  change 
of  place  is  probably  due  to  the  continual  death  and  decay  of  the  mature 
cells,  where  they  are  connected  with  the  fibres ;  and  the  constant  pro- 
duction of  new  generations  at  the  external  surface,— thus  carrying  the 
previously-formed  cells  inwards,  in  precisely  the  same  manner  that  the 
epidermic  cells  are  progressively  carried  outwards. 

15 


226  STRUCTURE  AND  ENDOWMENTS   OF  ANIMAL  TISSUES. 

389.  The  regeneration  of  Nervous  tissue  that  has  been  destroyed, 
takes  place  very  readily  in  continuity  with  that  which  is  left  sound. 
This  may  be  more  easily  proved  by  the  return  of  the  sensory  and  motor 
endowments  of  the  part,  whose  nerves  have  been  separated,  than  by 
microscopic  examination  of  the  reunited  trunks  themselves,  which  is 
not  always  satisfactory.  All  our  knowledge  of  the  functions  of  the 
nervous  system  leads  to  the  belief,  that  perfect  continuity  of  the  nerve- 
tubes  is  requisite  for  the  conduction  of  an  impression  of  any  kind, 
whether  this  be  destined  to  produce  motion  or  sensation ;  and  various 
facts,  well  known  to  Surgeons,  prove  that  such  restoration  may  be  com- 
plete. In  the  various  operations  which  are  practised  for  the  restoration 
of  lost  parts,  a  portion  of  tissue  removed  from  one  spot  is  grafted,  as  it 
were,  upon  another ;  its  original  attachments  are  more  or  less  completely 
severed, — frequently  altogether  destroyed, — and  new  ones  are  formed. 
Now  in  such  a  part,  so  long  as  its  original  connexions  exist,  and  the 
new  ones  are  not  completely  formed,  the  sensation  is  referred  to  the 
spot  from  which  it  was  taken  ;  thus  when  a  new  nose  is  made,  by  partly 
detaching  and  bringing  down  a  piece  of  skin  from  the  forehead,  the 
patient  at  first  feels,  when  anything  touches  the  tip  of  his  nose,  as  if  the 
contact  were  really  with  his  forehead.  After  time  has  been  given, 
however,  for  the.  establishment  of  new  connexions  with  the  parts  into 
whose  neighbourhood  it  has  been  brought,  the  old  connexions  of  the 
grafted  portion  are  completely  severed ;  and  an  interval  then  ensues, 
during  which  it  frequently  loses  all  sensibility ;  but  after  a  time  its 
power  of  feeling  is  restored,  and  the  sensations  received  through  it  are 
referred  to  the  right  spot.  A  more  familiar  case  is  the  regeneration  of 
Skin,  containing  sensory  nerves,  which  takes  place  in  the  well-managed 
healing  of  wounds  involving  loss  of  substance.  Here  there  must  ob- 
viously be,  not  merely  a  prolongation  of  the  nerve-tubes  from  the  sub- 
jacent and  surrounding  trunks,  but  also  a  formation  of  new  sensory 
papillae.  A  still  more  striking  example  of  the  regeneration  of  Nervous 
tissue,  however,  is  to  be  found  in  those  cases  (of  which  there  are  now 
several  on  record),  in  which  portions  of  the  extremities,  that  have  been 
completely  severed  by  accident,  have  been  made  to  adhere  to  the  stump  ; 
and  have,  in  time,  completely  recovered  their  connexion  with  the  Ner- 
vous as  with  the  other  systems,  as  is  indicated  by  the  restoration  of 
their  sensory  and  motor  endowments. — Of  the  degree  in  which  the  vesi- 
cular substance  of  the  Nervous  system  may  be  regenerated,  we  have  no 
certain  knowledge ;  but  there  can  be  little  doubt,  from  the  activity  of 
its  usual  nutritive  changes,  that  a  complete  reproduction  may  be  effected 
in  cases  of  loss  of  substance,  where  it  can  commence  from  a  neighbour- 
ing mass  of  the  same  tissue. 

390.  We  have  now  to  inquire  into  the  conditions,  under  which  the 
peculiar  properties  of  the  Nervous  System  are  manifested  in  an  active 
form  ;  and  it  will  first  be  desirable  to  explain,  somewhat  more  in  detail, 
the  nature  of  the  difi*erent  operations  to  which  it  is  subservient.  These 
operations  present  themselves  in  their  most  complex  form,  in  Man  and 
the  higher  animals ;  but  they  may  often  be  most  satisfactorily  studied 
in  the  lower.  In  the  first  place,  when  an  impression  is  made  upon  any 
part  of  the  surface  of  the  body  by  mechanical  contact,  by  heat,  elec- 


Ij  PROPERTIES    OF   NERVOUS   SYSTEM.  227 

tricity,  or  any  other  similar  agent, — or  upon  the  organs  of  special  sense 
(the  eye  and  ear,  the  nose  and  tongue),  by  light  or  sound,  by  odorous 
;   or  sapid  bodies, — these  impressions,  in  the  healthy  and  wakeful  state  of 
I   the  Nervous  system,  are  felt  as  sensations  ;  that  is,  the  mind  is  rendered 
;   conscious  of  them.     Now  there  can  be  no  doubt  that  the  mind  is  imme- 
i    diately  influenced,  not  by  the  impression  in  the  remote  organ,  but  by  a 
f   certain  change  in  the  condition  of  the  brain,  excited  or  aroused  by  that 
'    which  has  originated  elsewhere.     For  if  the  communication  with  the 
brain  be  cut  oft',  no  impression  on  the  distant  parts  of  the  nervous  system 
is  felt,  notwithstanding  that  the  mind  remains  perfectly  capable  of  re- 
ceiving it.    The  mind,  then,  is  only  rendered  conscious  of  external  objects, 
by  the  influence  which  they  exert  upon  the  hrain,  or  upon  a  certain  part 
of  it,  which,  being  the  peculiar  seat  of  sensation,  is  called  the  sensorium. 
Hence  we  recognise,  in  the  process  by  which  the  mind  is  rendered  con- 
scious of  external  objects,  three  distinct  stages ;  first,  the  reception  of 
the  impression  at  the  extremities  of  the  sensory  nerve ;  second,  the 
I    conduction   of  the  impression,   along  the  trunk  of  the  nerve,   to  the 
I    sensorium;    third,  the  change  excited  by  it  in  the  sensorium  itself, 
through  which  sensation  is  produced.     Here,  then,  the  change  in  the 
,    condition  of  the  nervous  system  commences  at  the  circumference,  and 
!    is  transmitted  to  the  centre ;  and  the  fibres  which  are  concerned  in  this 
ll^ransmission  are  termed  sensory. 

If  391.  On  the  other  hand,  when  an  emotion,  an  instinctive  impulse,  or 
^  an  act  of  the  will,  operates  through  the  central  organs  to  produce  a 
muscular  contraction,  the  first  change  is  in  the  condition  of  the  vesicular 
substance  of  those  organs.  The  influence  of  this  change  is  transmitted 
by  the  motor  nerves  to  the  muscles,  among  which  they  are  distributed ; 
and  the  desired  movement  is  the  result.  Here,  too,  we  have  at  least 
three  stages ;  first,  the  origination  of  the  change  by  an  impression  act- 
ing on  the  central  organ ;  second,  the  conduction  of  that  change  along 
the  motor  nerves  ;  and  third,  the  stimulation  of  the  muscles  to  contrac- 
tion. But  the  operation  here  commences  at  the  centre  ;  and  the  effects 
I  of  the  change  in  the  brain  are  transmitted  to  the  circumference,  by  a 
^  set  of  nervous  fibres  which  are  termed  motor.  The  complete  distinct- 
ness of  these  two  classes  of  fibres  was  first  established  by  Sir  C.  Bell. 
It  is  best  seen  in  the  nerves  of  the  head,  of  which  some  are  purely  sen- 
sory, and  others  purely  motor ;  but  it  may  also  .be  clearly  proved  to 
exist  at  the  roots  of  the  spinal  nerves  (although  their  trunks  possess 
mixed  endowments),  the  posterior  being  sensory,  wjailst  the  anterior  are 
motor. 

392.  But  although  sensations  can  only  be  felt  through  the  5mm,  and 
voluntary  motions  can  only  be  produced  by  an  action  of  the  mind  through 
the  same  organ,  yet  there  are  many  changes  in  the  animal  body,  in 
which  the  nervous  system  is  concerned,  which  yet  do  not  involve  the 
operation  of  the  brain,  being  produced  without  our  consciousness  being 
necessarily  excited,  and  without  any  act  of  the  will,  or  even  in  opposi- 
tion to  its  eff'orts.  Of  these  actions,  the  spinal  cord  of  Vertebrata,  and 
its  prolongation  within  the  cranium,  are  the  chief  instruments ;  in  the 
Invertebrate  animals,  they  are  performed  by  various  ganglia,  which  are 
usually  disposed  in  the  neighbourhood  of  the  organs  to  which   they 


228  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL    TISSUES. 

minister.  If  the  spinal  cord  of  a  Frog  be  divided  in  its  back,  above 
the  crural  plexus,  so  as  entirely  to  cut  oiF  the  nerves  of  the  lower  ex- 
tremities from  connexion  with  the  brain,  the  animal  loses  all  voluntary 
control  over  these  limbs,  and  no  sign  of  pain  is  produced  by  any  injury 
done  to  them.  But  they  are  not  thereby  rendered  motionless ;  for 
various  stimuli  applied  to  the  limbs  themselves  will  cause  movements  in 
them.  Thus  if  the  skin  of  the  foot  be  pinched,  or  if  a  flame  be  applied 
to  it,  the  leg  will  be  violently  retracted.  Or,  if  the  cloaca  be  irritated 
by  a  probe,  the  feet  will  endeavour  to  push  away  the  instrument.  We 
have  no  reason  hence  to  believe,  that  the  animal  feels  the  irritation,  or 
intends  to  execute  these  movements  in  order  to  escape  from  it;  for 
motions  of  a  similar  kind  are  exhibited  by  men,  who  have  suffered  injury 
of  the  lower  part  of  the  spinal  cord,  and  who  are  utterly  unconscious, 
either  of  the  irritation  which  their  limbs  receive,  or  of  the  actions  which 
they  perform. 

393.  We  are  not  to  suppose,  however,  that  the  stimulus  acts  at 
once  upon  the  muscles,  without  the  nervous  system  being  concerned  at 
all ;  throwing  them  into  contraction  by  its  direct  influence.  For  it  is 
quite  certain,  that  unless  the  nervous  trunks  remain  continuous  with 
the  spinal  cord,  and  unless  the  part  of  the  spinal  cord  wdth  which  they 
are  connected  remains  sound  (although  cut  off  from  connexion  with 
the  parts  above,  and  with  the  brain),  no  action  will  result.  If  the 
trunks  be  divided,  or  either  of  the  roots  by  which  they  are  connected 
with  the  spinal  cord  be  severed,  or  the  lower  portion  of  the  spinal 
cord  itself  be  injured,  no  stimulation  w-ill  cause  the  muscular  move- 
ments just  described.  A  very  good  example  of  this  necessity  for  the 
completeness  of  the  nervous  trunks,  which  convey  impressions  to  and 
from  the  central  organ,  is  found  in  the  movements  of  the  iris,  for  the 
contraction  and  dilatation  of  the  pupil.  Here  the  stimulus  of  light  upon 
the  retina  gives  rise  to  a  change  in  the  condition  of  the  optic  nerve ; 
which,  being  transmitted  to  a  certain  portion  of  the  encephalon  with 
which  that  nerve  is  connected,  excites  there  a  motor  impulse  ;  and 
this  impulse  is  conveyed  through  a  distinct  nerve  (a  branch  of  the 
third  pair)  to  the  iris,  occasioning  contraction  of  the  pupil.  Every  one 
knows  that  this  adjustment  of  the  size  of  the  pupil  to  the  amount  of 
light,  is  effected  without  any  exertion  of  the  will  on  his  own  part,  and 
even  without  any  consciousness  that  it  is  taking  place.  It  is  performed, 
too,  during  profound  sleep ;  when  the  influence  of  light  upon  the  retina 
excites  no  consciousness  of  its  presence, — when  no  sensation,  therefore, 
is  produced- by  it. 

394.  The  class  of  actions  thus  performed,  is  termed  reflex;  and  we 
see  that  every  such  action  involves  the  following  series  of  changes. 
In  the  first  place,  an  impression  is  made  upon  the  extremity  of  a 
nerve,  by  some  external  agent ;  just  as  when  sensation  is  to  be  pro- 
duced. Secondly,  this  impression  is  transmitted  by  a  nervous  trunk 
to  the  spinal  cord  in  Vertebrata,  or  to  some  ganglionic  mass  which 
answers  to  it  in  the  Invertebrata.  But  instead  of  being  communicated 
by  its  means  to  the  mind,  and  becoming  a  sensation,  it  immediately 
and  necessarily  executes  a  motor  impulse ;  which  is  reflected  back  as  it 
were   to  certain   muscles,  and,  by  their  contraction,  gives   rise  to  a 


CONDITIONS   OF   NERVOUS   ACTIONS.  229 

movement.  We  shall  hereafter  see,  that  nearly  all  those  movements  in 
the  animal  body,  which  are  immediately  connected  with  the  mainte- 
nance of  the  organic  functions, — such  as  those  of  respiration,  degluti- 
tion (or  swallowing),  the  expulsion  of  the  faeces,  urine,  and  foetus,  &o. 
— are  performed  in  this  manner. 

395.  Now  there  is  strong  reason  to  believe  that  the  changes  which 
take  place  in  the  nervous  trunks  are  of  the  same  nature,  whatever  may 
be  the  source  from  which  they  proceed, — ^whether,  for  example,  the 
movement  is  simply  reflex,  whether  it  proceed  from  a  mental  emotion, 
or  whether  it  be  executed  in  obedience  to  an  act  of  the  will.  It  Was 
formerly  supposed  that  all  the  afferent  or  centripetal  fibres  pass  up  to 
the  Brain,  and  that  all  the  efferent  or  centrifugal  fibres  pass  down  from 
the  same  organ ;  the  Spinal  Cord  being  looked  upon  as  little  else  than 
a  bundle  of  nerves.  It  is  now  known,  however,  that  by  far  the  greater 
part  of  the  fibres  of  any  trunk  terminates  in  the  central  organ,  to  which 
that  trunk  at  first  proceeds ;  and  that  the  Spinal  Cord  may  be  consi- 
dered as  a  series  of  such  ganglionic  centres,  each  receiving  the  aflferent 
fibres,  and  giving  origin  to  the  efferent,  of  its  own  segment.  So, 
again,  the  special  sensory  nerves,  the  olfactive,  optic,  auditory,  and 
gustative,  terminate  in  their  own  ganglionic  centres,  which  lie  at  the 
base  of  the  brain,  in  immediate  connexion  with  the  summit  of  the 
spinal  cord,  and  which  are  quite  independent  of  the  cerebrum.  The 
apparatus  for  receiving  impressions,  and  for  originating  motions,. is  thus 
complete  in  itself;  and  the  addition  of  the  cerebrum  does  not  make 
any  essential  difi'erence  in  its  operations,  save  that  this  sensori-motor 
apparatus  (as  it  may  be  termed)  is  made  to  act  through  its  means  as 
the  agent  of  the  mind,  in  addition  to  its  functions  as  the  instrument  of 
the  automatic  movements.  We  shall  hereafter  see  (chap,  xii.),  that 
the  difi'erence  between  Instinct  and  Intelligence  is  closely  connected 
with  the  development  of  the  cerebrum  ;  but  that  this  organ,  even  in 
that  highest  grade  of  development  which  it  possesses  in  Man,  has  no 
other  connexion  with  the  sensory  organs  than  that  which  it  acquires 
through  its  relation  with  the  sensory  ganglia,  and  has  no  more  power  of 
exciting  muscular  movement,  than  by  playing  (so  to  speak),  upon  the 
spinal  cord,  whose  eff'erent  fibres  respond  to  its  mandates,  just  as  they 
would  do  to  the  stimulus  of  an  impression  primarily  acting  through  that 
organ. 

396.  Of  the  mode  by  which  the  eff"ects  of  changes  in  one  part  of  the 
Nervous  system,  are  thus  instantaneously  transmitted  to  another, 
nothing  whatever  is  known.  There  is  evidently  a  strong  analogy  between 
this  phenomenon,  and  the  instantaneous  transmission  of  the  Electric 
power  along  good  conductors ;  but  the  relation  is  much  more  intimate 
than  this,  for  Electricity  is  capable  of  exciting  Nerve-force,  whilst, 
conversely.  Nerve-force  can  excite  Electricity.  Thus,  a  very  feeble 
galvanic  current  transmitted  along  a  motor  nerve,  serves  to  excite  con- 
tractions in  the  muscles  supplied  by  it ;  and  in  like  manner,  a  galvanic 
current  transmitted  along  any  of  the  sensory  nerves,  gives  rise  to  a 
sensation  of  the  kind  to  which  the  nerve  ministers.  Moreover  we 
shall  hereafter  see,  that  certain  animals  are  capable  of  generating 
Electric  power  in  a  very  remarkable  manner  (chap,  x.) ;  and  that  the 


280  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

nervous  force  is  essentially  concerned  in  this  operation.  But,  on  the 
other  hand,  it  is  quite  certain  that  the  influence  transmitted  along  the 
nerves  of  the  living  body  is  not  ordinary  electricity ;  for  all  attempts 
to  procure  manifestations  of  electric  changes  in  the  state  of  nerves, 
that  are  acting  most  energetically  on  muscles,  have  completely  failed ; 
and  a  nerve  remains  capable  of  conveying  the  influence  of  electricity, 
when  it  has "  been  rendered  unable  to  transmit  the  influence  of  the 
brain,  as  by  tying  a  ligature  round  it,  or  by  tightly  compressing  it 
between  the  forceps,  which  gives  no  interruption  to  the  one  agency, 
while  it  completely  checks  the  other. — Notwithstanding,  then,  the  strong 
analogy  which  exists  between  these  two  powers,  we  are  not  warranted 
in  regarding  them  as  identical;  but  they  have  towards  each  other  that 
relation  of  reciprocity,  which  exists  between  Electricity  and  Heat,  or 
between  Electricity  and  Magnetism,  each  being  convertible  into  the 
other  in  a  certain  definite  ratio  (§  53). 

397.  It  is  more  desirable,  however,  that  we  should  understand  the 
conditions  under  which  the  phenomena  of  the  Nervous  System  take 
place,  than  that  we  should  spend  much  time  in  discussing  the  identity 
of  its  peculiar  powers  with  any  others  in  Nature.  The  conducting 
power  of  the  nervous  fibres  appears  to  remain  with  little  decrease  for 
some  time  after  death,  especially  in  cold-blooded  animals ;  for  we  can, 
by  pinching,  pricking,  or  otherwise  stimulating  the  motor-trunk,  give 
rise  to  contractions  in  the  muscles  supplied  by  them,  exactly  as  during 
life.  This  power  is  much  lessened  by  the  influence  of  narcotics  ;  so  that 
if  a  nervous  trunk  be  soaked  in  a  solution  of  opium,  belladonna,  or  other 
powerful  narcotic,  it  ceases  to  be  able  to  convey  the  efiects  of  stimuli  to 
the  muscles,  some  time  before  the  muscles  themselves  lose  their  con- 
tractile power.  On  the  other  hand,  it  seems  to  be  exalted  by  various 
irritating  influences  ;  so  that,  when  the  nervous  trunk  has  been  treated 
with  strychnia,  or  when  it  has  been  subjected  to  undue  excitement  in  other 
ways,  a  very  slight  change  is  magnified  (as  it  were)  during  its  transmis- 
sion, and  produces  eff'ects  of  unusual  intensity. 

398.  Now  although  the  conducting  power  of  the  fibrous  structure 
will  continue  for  a  time,  after  the  circulation  through  it  has  ceased,  the 
peculiar  endowments  of  the  vesicular  substance,  by  which  it  originate% 
the  changes  which  the  former  transmits,  are  only  manifested,  when 
blood  is  moving  through  its  capillaries.  Thus  if  the  circulation  through 
the  brain  cease  but  for  a  moment,  total  insensibility,  and  loss  of  the  power 
of  voluntary  motion,  immediately  supervene.  The  brain  is  supplied 
with  blood  through  four  arteries, — the  two  internal  carotids,  and  the 
two  vertebrals ;  and  by  the  communication  of  these  with  each  other 
through  the  circle  of  Willis,  the  circulation  will  still  be  kept  up,  if  only 
one  of  them  should  convey  blood  into  the  cavity  of  the  cranium.  Hence 
it  is  necessary  that  the  flow  of  blood  should  be  checked  through  all  of 
them,  in  order  that  the  functions  of  the  brain  should  be  suspended ;  and 
the  suspension  is  then  complete  and  instantaneous.  The  best  method 
of  effecting  this  was  devised  by  Sir  Astley  Cooper.  He  tied  both  the 
carotid  arteries  in  a  dog :  which,  for  the  reasons  just  mentioned,  did 
not  produce  any  decided  influence  on  the  functions  of  the  brain,  the 
circulation  being  kept  up  through  the  vertebrals.     But  upon  compress- 


r 


EFFECTS   OF   STIMULANTS   UPON  NERVOUS   POWER.  231 


ing  the  latter,  so  as  to  suspend  the  flow  of  blood  through  them,  imme-^ 
diate  insensibility,  and  loss  of  voluntary  power,  were  the  result.  When 
the  compression  was  taken  off,  the  animal  immediately  returned  to  its 
usual  state  ;  and  again  became  suddenly  insensible,  when  the  pressure 
was  renewed.  Although  the  functions  of  the  brain  were  thus  suspended, 
those  of  the  spinal  cord  were  not ;  as  was  shown  by  the  occurrence  of 
convulsive  movements.  But  in  the  state  called  Syncope,  or  fainting, 
the  suspension  of  the  circulation,  by  a  failure  in  the  heart's  action, 
causes  an  entire  loss  of  power  in  both  these  centres ;  and  a  complete 
cessation  of  muscular  movement  is  the  result.  This  condition  may 
come  on  instantaneously,  under  the  influence  of  powerful  mental  emo- 
tion, or  of  some  other  cause,  which  acts  primarily  in  suspending  the 
heart's  action,  and  consequently  in  checking  the  circulation ;  the  insen- 
sibility, and  loss  of  muscular  power,  are  secondary  results,  depending 
upon  the  suspension  of  the  powers  of  the  nervous  centres,  consequent 
upon  the  cessation  of  the  flow  of  blood  through  them. 

399.  The  due  activity  of  the  vesicular  nervous  matter  is  not  only 
dependent  upon  a  sufficient  supply  of  blood,  but  it  requires  that  this 
blood  should  be  in  a  state  of  extreme  purity  ;  for  there  is  no  tissue  in 
the  body,  whose  functions  are  so  readily  deranged,  by  any  departure 
from  the  regular  standard  in  the  circulating  fluid, — whether  this  con- 
sist in  the  alteration  of  the  proportions  of  its  normal  ingredients,  or  in 
the  introduction  of  other  substances  which  have  no  proper  place  in  it. 
One  of  the  most  fertile  sources  of  disturbance  in  the  action  of  the 
brain,  consists  in  the  retention  of  substances  within  the  blood,  which 
ought  to  be  excreted  from  it.  We  shall  hereafter  see,  that  three  of 
the  largest  and  most  important  organs  in  the  body, — the  lungs,  the 
liver,  and  the  kidneys, — ^liave  it  for  their  special  office,  to  separate 
from  the  circulating  fluid  the  products  of  the  decomposition,  which  is 
continually  taking  place  in  the  body;  and  thereby  to  maintain  its 
purity  and  its  fitness  for  its  important  functions.  Now  if  these,  from 
any  cause,  even  partially  fail  in  their  office,  speedy  disturbance  of  the 
functions  of  the  nervous  centres  is  the  result.  Thus  if  the  lungs  do 
not  purify  the  venous  blood  of  its  impregnation  of  carbonic  acid,  or 
restore  to  it  the  proper  proportion  of  oxygen,  the  functions  of  the  brain 
are  seriously  aff'ected.  The  sensations  become  indistinct,  the  will  loses 
its  control  over  the  muscles,  giddiness  and  faintness  come  on,  and  at 
last  complete  insensibility  supervenes.  Corresponding  symptoms  occur, 
though  to  a  less  serious  degree,  when  the  excretion  of  carbonic  acid  is 
but  slightly  impeded.  Thus  when  a  number  of  persons  are  shut  up  in 
an  ill-ventilated  apartment,  for  a  sufficient  length  of  time  to  raise  the 
proportion  of  carbonic  acid  in  the  air  to  1  or  2  per  cent.,  the  continued 
purification  of  their  blood  by  respiration  is  but  insufficiently  performed, 
for  reasons  which  will  be  stated  hereafter  (chap,  viii.) ;  and  the  car- 
bonic acid  accumulates  in  their  blood  in  a  sufficient  degree,  to  produce 
headache  and  obtuseness  of  the  mental  powers.— Similar  results  take 
place,  as  will  be  shown  hereafter,  from  the  retention  of  the  substances 
which  ought  to  be  drawn  off"  by  the  liver  and  kidneys ;  these,  when  they 
accumulate  in  even  a  trifling  degree,  produce  torpor  of  the  functions  of 
the  brain ;  and  when  their  proportion  increases,  complete  cessation  of 


232  STRUCTURE  AND   ENDOWMENTS   OF  ANIMAL  TISSUES. 

its  powers  is  the  result,  their  action  being  precisely  that  of  narcotic 
poisons.  Various  substances  introduced  into  the  blood  may  exert  similar 
influences ;  depressing  the  activity  of  the  vesicular  substance  of  the 
nervous  centres,  and  consequently  producing  torpidity,  not  merely  in 
regard  to  the  reception  of  impressions,  and  the  performance  of  volun- 
tary motions,  but  also  in  the  mental  operations  generally. 

400.  On  the  other  hand,  various  coi;iditions  of  the  blood,  especially 
those  depending  on  the  presence  of  certain  external  agents,  produce  an 
undue  energy  in  the  functions  of  the  nervous  centres ;  which  energy, 
however,  is  almost  invariably  accompanied  by  irregularity,  or  want  of 
balance  among  the  diff'erent  actions.  Of  this  we  have  a  familiar  example 
in  the  operation  of  alcohol.  Its  first  effect,  when  taken  in  moderate 
quantity,  is  usually  to  produce  a  simple  increase  in  the  activity  of  the 
cerebral  functions.  A  further  dose,  however,  occasions  not  merely  an 
increase,  but  an  irregularity ;  destroying  that  power  of  self-control,  which 
is  so  important  a  means  of  balancing  the  different  tendencies  in  the 
healthy  condition  of  the  mind.  And  a  still  larger  dose  has  the  effect 
of  a  narcotic  poison  ;  producing  diminution  or  suspension  of  activity  in 
all  the  functions  of  the  brain.  In  some  persons,  this  is  the  mode  in 
which  the  alcohol  acts  from  the  first,  its  stimulating  effects  being  altogether 
wanting. — A  similar  activity  is  usually  produced  by  the  respiration  of 
the  Nitrous  Oxide,  which  seems  to  increase  all  the  powers  of  the  mind, 
save  that  of  self-control,  which  it  diminishes  ;  the  individual,  while  under 
its  influence,  being  the  slave  of  his  impulses,  which  act  on  his  muscular 
system  with  astonishing  energy.  Very  analogous  to  this,  is  the  incipient 
stage  of  mania ;  which  is  simply  an  undue  energy  of  the  cerebral  func- 
tions at  first  in  some  degree  under  the  control  of  the  will,  but  after- 
wards increasing  to  an  extent  that  renders  the  individual  completely 
powerless  over  himself;  and  showing  itself  in  the  intensity  of  the  sensa- 
tions produced  by  external  objects,  in  the  vividness  of  the  trains  of 
thought  (which,  being  entirely  uncontrolled,  succeed  each  other  with 
apparent  irregularity,  though  probably  according  to  the  laws  of  associa- 
tion and  suggestion),  and  in  the  violence  of  the  muscular  actions.  Such 
a  state  may  continue  for  some  time,  without  the  intervention  of  sleep ; 
but  the  subsequent  exhaustion  of  nervous  power  is  proportioned  to  the 
duration  of  the  excitement;  and  frequent  attacks  of  mania  almost 
invariably  subside  at  last  into  imbecility. 

401.  In  these  cases  of  undue  excitement,  there  is  obviously  an  increase 
in  the  supply  of  blood  to  the  head ;  as  indicated  by  the  suffusion  of  the 
face,  the  injection  of  the  conjunctiva,  the  throbbing  at  the  temples,  the 
pulsation  of  the  carotids ;  and  we  find  that  measures  which  diminish 
the  activity  of  the  circulation  through  the  brain,  are  those  most  effec- 
tual in  subduing  the  excitement.  But  it  does  not  at  all  follow,  that 
this  undue  action  of  the  brain  should  be  connected  with  an  excess  in  the 
whole  amount  of  nutritive  material,  and  should  require  general  deple- 
tion for  its  treatment.  In  fact,  a  very  similar  class  of  symptoms  may 
present  itself  under  two  conditions  of  an  entirely  opposite  kind,— 
inflammation,  accompanied  with  an  increase  in  the  proportion  of  fibrine 
m  the  blood,  and  requiring  treatment  of  a  lowering  kind,— and  irritation, 
depending  on  a  state  of  blood  in  which  there  is  a  deficiency  of  solid 


DEPENDENCE  OP  NERVOUS  POWER  ON  SUPPLY  OF  BLOOD.    233 

materials,  and  requiring  a  strengthening  and  even  a  stimulating  regimen. 
The  skill  of  the  practitioner  is  often  put  to  the  test,  in  the  due 
discrimination  between  these  states. 

402.  The  preceding  examples  mark  the  influence  of  various  causes 
upon  the  actions  of  the  vesicular  matter  of  the  hrain  ;  others  might  be 
adduced  to  show,  that  the  vesicular  substance  of  the  spinal  cord  is  also 
liable  to  have  its  powers  depressed  or  excited ;  but  these  will  be  best 
adverted  to  hereafter,  when  the  distinct  functions  of  that  organ  are 
under  consideration  (chap,  xii.)  We  may  simply  notice,  that  the  stimu- 
lating effect  of  Strychnia  is  peculiarly  and  most  remarkably  exerted 
upon  the  vesicular  substance  of  the  spinal  cord ;  and  that  a  correspond- 
ing state,  in  which  violent  convulsive  actions  are  excited  by  the  most 
trifling  causes,  sometimes  presents  itself  as  a  peculiar  form  of  disease, 
named  Tetanus,  which  may  be  either  idiopathic,  depending  probably 
upon  a  disordered  condition  of  the  blood,  or  traumatic,  consequent  upon 
the  irritation  of  a  wound. 

403.  But,  as  formerly  remarked,  it  is  not  in  the  Nervous  centres 
only,  that  changes  originate.  Whenever  an  impression  is  made  upon 
the  surface  of  the  body,  or  upon  the  organs  of  special  sense,  which, 
being  conducted  to  the  nervous  centres,  either  excites  a  sensation  in  the 
brain  (§  390),  or  a  reflex  action  through  the  spinal  cord  (§  392),  the 
reception  and  propagation  of  such  impression  at  the  extremities  of  the 
sensory  nerves  requires  a  set  of  conditions  of  the  same  kind  with  those, 
which  we  have  seen  to  exist  in  the  nervous  centres.  In  fact,  if  we  re- 
gard the  course  of  the  motor  nerves  as  commencing  in  tlie  nervous 
centres  and  terminating  in  the  muscles,  we  may  with  equal  justice  con- 
sider that  of  the  sensor^/  nerves  as  originating  in  their  peripheral  extremi- 
ties, and  terminating  in  the  sensorium.  And,  as  already  stated  (§  381), 
precisely  the  same  kind  of  vesicular  structure  exists  in  some  (probably 
in  all)  of  the  peripheral  expansions  of  the  sensory  nerves,  as  makes  up 
the  gray  substance  of  the  brain  and  spinal  cord.  Now  it  is  easily  shown, 
that  the  circulation  of  the  blood  through  these  parts  is  just  as  necessary 
for  the  original  reception  of  the  impressions,  as  is  the  circulation  through 
the  brain  to  their  reception  as  sensations,  and  to  the  origination  of 
motor  impulses  by  an  act  of  the  will.  We  find  that  anything  which 
retards  the  circulation  through  a  part  supplied  by  sensory  nerves, 
diminishes  its  sensibility ;  and  that  if  the  flow  of  blood  be  completely 
stagnated,  entire  insensibility  is  the  result.  A  familiar  example  of  this 
is  seen  in  the  eff'ects  of  prolonged  cold ;  which,  by  diminishing,  and 
then  entirely  checking,  the  flow  of  blood  through  the  skin,  produces 
first  numbness,  and  then  complete  insensibility  of  the  part.  This  result, 
however,  may  be  partly  due  to  the  direct  influence  of  the  cold  upon  the 
nerve-vesicles  themselves ;  depressing  their  peculiar  vital  powers  (§  97). 
The  same  effect  is  produced,  however,  when  the  supply  of  blood  is 
checked  in  any  other  way ;  as,  for  example,  by  pressure  on  the  artery, 
or  by  obstruction  in  its  interior.  Thus  when  the  main  artery  of  a  limb 
is  tied,  numbness  of  the  extremities  is  immediately  perceived ;  and  this 
continues,  until  the  circulation  is  re-established  by  the  collateral  branches, 
when  the  usual  amount  of  sensibility  is  restored.  Again,  in  the  gan- 
grene which  depends  upon   obstruction  of  the  arterial  trunks  by  a 


234  STRUCTURE  AND   ENDOWMENTS  OF  ANIMAL  TISSUES. 

fibrinous  clot  in  their  interior,  diminution  of  sensibility,  consequent  upon 
the  insufficient  circulation,  is  one  of  the  first  symptoms. 

404.  On  the  other  hand,  increased  circulation  of  blood  through  a 
part  produces  exaltation  of  its  sensibility;  that  is,  the  ordinary  im- 
pressions produce  changes  of  unusual  energy  in  its  sensory  nerves. 
This  is  particularly  evident  in  the  increased  sensibility  of  the  genital 
organs  of  animals  during  the  period  of  heat ;  and  in  those  of  Man, 
when  in  a  state  of  venereal  excitement.  Moderate  warmth,  friction, 
exercise,  and  other  causes  which  increase  the  circulation  through  a  part, 
also  augment  its  sensibility ;  and  this  augmentation  is  one  of  the  most 
constant  indications  of  that  state  of  determination  of  blood,  or  active 
congestion,  which  usually  precedes  inflammation,  and  which  exists  in  the 
parts  surrounding  the  centre  of  inflammatory  action.  But  it  must  be 
borne  in  mind,  here  as  elsewhere  (§  401),  that  such  exaltation  of  func- 
tion in  a  limited  part,  is  quite  consistent  with  general  debility ;  and  in 
fact  we  may  often  observe,  that  the  tendency  of  such  local  afiections 
is  particularly  great,  when  the  blood  is  in  a  very  poor  condition.     (See 

CHAP.  V.) 

405.  To  sum  up,  then,  we  may  compare  the  vesicular  substance, 
wherever  it  exists,  to  a  galvanic  combination  :  the  former  being  capable 
of  generating  nervous  influence,  and  transmitting  it  along  the  fibrous 
structure,  to  the  part  on  which  it  is  to  operate ;  in  the  same  manner 
as  the  latter  generates  electric  power,  and  transmits  it  along  the  con- 
ducting wires,  to  the  point  at  which  it  is  to  eff"ect  a  decomposition  or 
any  other  change.  In  one  of  the  most  perfect  forms  of  the  galvanic 
battery  (that  invented  by  Mr.  Smee)  although  the  metals  remain  in- 
serted in  the  acid  solution,  and  are  consequently  always  ready  for 
action,  no  electricity  is  generated  until  the  circuit  is  complete ;  and  the 
waste  of  the  zinc,  produced  by  its  solution  in  the  acid,  is  therefore 
exactly  proportional  to  the  electric  efiects  to  which  it  gives  rise.  The 
condition  of  the  nervous  system,  in  the  healthy  and  waking  state,  bears 
a  close  analogy  to  this ;  for  it  is  in  a  state  constantly  ready  for  action, 
but  waits  to  be  excited ;  and  its  waste  is  proportional  to  the  activity  of 
its  function. — The  vesicular  matter,  diff'used  over  the  surface  of  the 
body,  is  inactive,  until  an  impression  is  made  upon  it  by  some  external 
agent;  but  a  change  then  takes  place  in  its  condition  (of  which  we 
know  no  more,  than  that  the  presence  of  arterial  blood  and  a  certain 
amount  of  warmth  are  necessary  for  it),  which  is  transmitted  to  the 
central  organs  by  the  sensory  trunks.  It  would  appear  that  the  excite- 
ment of  this  change  has  a  tendency  to  increase  the  afflux  of  blood  to 
the  part ;  thus  when  a  lozenge  or  some  similar  substance  is  allowed  to 
lie  for  a  time  in  contact  with  the  tongue,  or  with  the  side  of  the  mouth, 
a  roughness  is  produced,  which  is  due  to  the  erection  of  the  sensory 
papillae,  by  the  distension  of  their  blood-vessels. — On  the  other  hand, 
the  change  in  the  vesicular  matter  of  the  central  organs,  by  which 
motion  is  produced  in  the  distant  muscles,  may  be  excited  either  by  the 
stimulus  conveyed  by  the  afi"erent  nerves  (as  in  reflex  action,  §  392),  or 
by  an  act  of  Mind.  This  act  may  be  voluntary,  originating  in  the  will ; 
or  it  may  be  instinctive  or  emotional,  resulting  from  certain  states  of 


CONNEXION  BETWEEN  THE  MIND  AND  BRAIN.        235 

mind  excited  by  sensations,  and  altogether  independent  of  the  will. 
Of  the  mode  in  which  the  mind  thus  acts  upon  the  nervous  system,  we 
know  nothing  whatever,  and  probably  never  shall  be  informed  in  our 
present  state  of  being.  But  it  is  sufficient  for  us  to  be  aware  of  the 
physiological  fact  of  the  peculiar  connexion  between  the  mind  and  the 
brain  ;  a  connexion  so  intimate,  as  to  enable  the  mind  to  receive  through 
the  body  a  knowledge  of  the  condition  of  the  Universe  around  it,  and 
to  impress  on  the  body  the  results  of  its  own  determinations  ;  and  of 
such  a  nature,  that  the  regularity  of  the  working  of  the  mind  itself  is 
dependent  upon  the  complete  organization  of  the  brain  in  the  first  in- 
stance, upon  the  constant  supply  of  pure  and  well-elaborated  blood,  and 
upon  all  those  influences  which  favour  the  due  performance  of  the 
nutritive  operations  in  general. 


BOOK  IL 

SPECIAL    PHYSIOLOGY. 


CHAPTER  IV. 

OF    FOOD,     AND     THE    DIGESTIVE     PROCESS. 
1.   Sources  of  the  Demand  for  Aliment. 

406.  The  dependence  of  all  Organized  beings  upon  food  or  aliment, 
must  be  evident  from  the  facts  stated  in  the  preceding  portion  of  this 
Treatise.  In  the  first  place,  the  germ  requires  a  large  and  constant 
supply  of  materials,  with  which  it  may  develope  itself  into  the  perfect 
being,  by  the  properties  with  which  it  is  endowed.  In  all  but  the 
lowest  tribes  of  Plants,  we  find  the  materials  required  for  the  earliest 
stages  of  the  process  prepared  and  set  apart  by  the  parent.  Thus  in 
the  seedj  the  germ  itself  forms  but  a  small  proportion  of  tho  whole 
substance,  the  principal  mass  being  composed  of  starchy  matter,  which 
is  laid  up  there  for  its  nutrition ;  and  the  act  of  germination  consists  in 
the  appropriation  of  that  nutriment  by  the  germ,  and  the  consequent 
development  of  the  latter,  up  to  the  point  at  which  it  becomes  inde- 
pendent of  such  assistance,  and  is  able  for  itself  to  procure,  from  the 
soil  and  atmosphere  that  surround  it,  the  materials  for  its  continued 
growth.  So  in  the  egg  of  the  Animal,  the  principal  mass  is  composed 
of  Albumen  and  oily  matter ;  the  germ  itself  being,  at  the  time  the  egg 
is  first  deposited,  a  mere  point  invisible  to  the  naked  eye  ;  these  mate- 
rials serve  as  the  food  or  aliment  of  the  germ,  which  gradually  draws 
them  to  itself,  and  converts  them  into  the  materials  of  its  own  struc- 
ture ;  and  at  the  end  of  a  certain  period,  the  young  animal  comes  forth 
from  the  egg,  ready  to  obtain  for  itself  the  food  which  is  necessary  for 
its  continued  increase  in  size. 

407.  In  many  instances  among  the  lower  animals,  the  form  in  which 
the  young  animal  emerges  from  the  egg  is  very  different  from  that 
which  it  is  subsequently  to  assume  ;  and  the  latter  is  only  attained  by 
a  process  of  metamorphosis.  This  change  has  been  longest  known,  and 
most  fully  studied,  in  the  case  of  Insects  and  Frogs ;  which  were  for- 
merly thought  to  constitute  an  exception  to  all  general  rules  in  this 
respect, — the  Insect  coming  forth  from  the  egg  in  the  state  of  a  Worm, 


SOURCES   OF   DEMAND   FOR   FOOD.  237 

and  the  Frog  in  the  condition  of  a  Fish.  But  it  is  now  known  that 
changes  of  form,  as  complete  as  these,  occur  in  a  large  proportion  of 
the  lower  tribes  of  Animals ;  so  that  the  absence  of  them  is  the  excep- 
tion. The  fact  seems  to  be,  that  the  supply  of  nutriment  laid  up  within 
the  egg,  among  the  lower  classes,  is  by  no  means  sufficient  to  carry  on 
the  embryo  to  the  form  it  is  subsequently  to  attain ;  and  its  development 
is  so  arranged,  that  it  may  come  into  the  world  in  a  condition  which 
adapts  it  to  obtain  its  own  nutriment,  and  thus  to  acquire  for  itself  the 
materials  for  its  further  development.  Thus  the  Insect,  in  its  larva  or 
Caterpillar  state,  is  essentially  a  foetus  in  regard  to  its  grade  of  develop- 
ment ;  but  it  is  a  foetus  capable  of  acquiring  its  own  food.  In  this  con- 
dition it  attains  its  full  growth  as  regards  size,  though  its  form  remains 
the  same ;  but  it  then,  in  passing  into  the  Chrysalis  state,  reassumes  (as 
it  were)  the  condition  of  an  embryo  within  the  egg, — the  development 
of  various  new  parts  takes  place,  at  the  expense  of  the  nutriment  stored 
up  in  its  tissues, — and  it  comes  forth  as  the  perfect  Insect.  In  many 
of  the  lower  tribes,  the  animal  quits  the  Qgg  at  a  still  earlier  period  in 
comparison ;  thus  it  has  been  lately  shown  by  M.  Milne  Edwards,  that 
some  of  the  long  marine  worms  consist  only  of  a  single  segment,  form- 
ing a  kind  of  head,  when  they  leave  the  egg ;  and  that  the  other  seg- 
ments, to  the  number  (it  may  be)  of  several  hundred,  are  gradually 
developed  from  this,  by  a  process  that  resembles  the  budding  of  Plants. 

408.  Up  to  the  period,  then,  when  the  full  dimensions  of  the  body 
have  been  attained,  and  the  complete  evolution  of  all  its  organs  has  taken 
place,  a  due  supply  of  food  is  necessary  for  these  purposes.  In  the 
Plant,  nearly  the  whole  of  the  alimentary  materials  taken  into  the 
system,  are  thus  appropriated ;  the  extension  of  its  structure  going  on 
almost  indefinitely,  and  the  waste  occasioned  by  decay  being  compara- 
tively small.  Thus  the  carbon,  which  is  given  out  by  the  respiratory 
process  in  the  form  of  carbonic  acid,  bears  but  a  small  proportion  to 
that  which  is  introduced  by  the  decomposition  of  that  same  gas,  under 
the  influence  of  light  (§  81).  And  the  fall  of  the  leaves,  which  takes 
place  once  a  year  or  more  frequently,  and  which  gives  back  a  large 
quantity  of  the  matter  that  has  undergone  the  organizing  process,  does 
not  occur,  until  by  their  means  a  considerable  addition  has  been  made 
to  the  solid  and  permanent  substance  of  the  tree. 

409.  This  is  not  the  case,  however,  with  the  animal.  Its  period  of 
increase  is  limited.  The  full  size  of  the  body  is  usually  attained,  and 
all  the  organs  acquire  their  complete  evolution,  at  a  comparatively  early 
period.  The  continued  supply  of  food  is  not  the''n  requisite  for  the  ex- 
tension of  the  structure,  but  simply  for  its  maintenance ;  and  the  source 
of  the  demand  lies  in  the  constant  waste,  to  which,  during  its  period  of 
activity,  it  is  subjected.  We  have  seen  that  every  action  of  the 
Nervous  and  Muscular  systems  involves  the  death  and  decay  of  a  cer- 
tain amount  of  the  living  tissue, — as  is  indicated  by  the  appearance  of 
the  products  of  that  decay  in  the  Excretions ;  and  a  large  part  of  the 
demand  for  food  will  be  consequently  occasioned  by  the  necessity  for 
making  good  the  loss  thus  sustained.  Hence  we  find  that  the  demand 
for  food  bears  a  close  relation  to  the  activity  of  the  animal  functions ; 
so  that  a  diet,  which  would  be  superfluous  and  injurious  to  an  individual 


238  OF  FOOD  AND    THE   DIGESTIVE   PROCESS. 

of  inert  habits,  is  suitable  and  beneficial  to  one  who  is  leading  a  life  of 
continual  exertion ;  and  this  diflference  manifests  itself  in  the  require- 
ments of  the  same  individual  who  makes  a  change  in  his  habits — the 
indolent  man  acquiring  an  appetite  by  vigorous  exertion,  and  the  active 
man  losing  his  disposition  to  hearty  feeding  by  any  cause  that  keeps 
him  from  his  accustomed  exercise.  We  see  precisely  the  same  contrast 
between  Animals  of  different  tribes,  whose  natural  instincts  lead  them 
to  different  modes  of  life.  The  Birds  of  most  active  flight,  and  the 
Mammals  which  are  required  to  put  forth  the  greatest  efforts  to  obtain 
their  food,  need  the  largest  and  most  constant  supplies  of  nutriment ; 
but  even  the  least  active  of  these  classes  stand  in  remarkable  contrast 
with  the  inert  Reptiles,  whose  slow  and  feeble  movements  are  attended 
with  so  little  waste,  that  they  can  sustain  life  for  weeks  and  even 
months,  with  little  or  no  diminution  of  their  usual  activity,  without  a 
fresh  supply  of  food. 

410.  The  waste  and  decay  just  adverted  to,  however,  do  not  affect 
the  muscular  and  nervous  tissues  alone;  for  all  the  operations  of  nutri- 
tion involve  it  to  a  certain  extent.  It  has  been  already  shown  that  the 
acts  of  absorption,  assimilation,  respiration,  secretion,  and  reproduction ; 
— all  those,  in  fact,  by  which  the  material  for  the  nutrition  of  the 
nervous  and  muscular  tissues  is  first  prepared,  and  subsequently  main- 
tained in  the  requisite  purity, — are  effected  in  the  Animal,  as  in  the 
Plant,  by  the  agency  of  cells,  which  are  continually  dying  and  requiring 
renewal.  In  most  Vegetables,  the  death  of  the  parts  concerned  in 
these  functions  takes  place  simultaneously,  as  soon  as  they  have  per- 
formed them ;  the  whole  crop  of  leaves  ceasing  at  once  to  perform  its 
proper  actions,  and  dropping  off; — to  be  replaced  by  another,  at  an  in- 
terval that  solely  depends  upon  the  temperature  under  which  the  tree 
is  living  (§  99).  In  the  evergreen,  however,  the  process  bears  a  close 
resemblance  to  that  which  we  observe  in  the  Animal ;  for  the  leaves  die 
one  by  one,  and  not  simultaneously ;  and  are  constantly  undergoing  re- 
placement, so  that  the  vigour  of  the  system  and  the  activity  of  its 
nutritive  processes  never  suffer  a  complete  suspension. 

411.  In  the  Animal  body,  the  different  classes  of  cells,  to  which 
allusion  has  been  made,  are  in  like  manner  constantly  undergoing  death 
and  renewal ;  and  this  with  a  rapidity  proportioned  to  the  energy  of 
their  functions.  ^  Hence  a  supply  of  food  is  as  requisite,  to  furnish  the 
materials  of  their  growth,  as  it  is  in  Plants  to  furnish  the  materials  of 
the  growth  of  the  leaves.  A  large  part  of  these  materials  are  subse- 
quently used  for  other  purposes  in  the  economy ;  thus,  as  the  leaves 
prepare  the  sap  which  is  to  nourish  the  woody  stem,  and  to  form  new 
shoots,  so  do  the  absorbing  and  assimilating  cells  prepare  and  furnish 
the  fluid  elements  of  the  blood,  which  are  to  repair  the  waste  of  nerve 
and  muscle,  bone  and  cartilage,  &c.  But  still  a  considerable  amount  is 
expended^  in  the  simple  nutrition  of  these  organs  themselves,  whose 
duration  is  transient,  and  whose  solid  parts  are  cast  off  as  of  no  further 
use.  Thus  the  skin  and  all  the  mucous  surfaces  are  continually  form- 
ing and  throwing  off  epidermic  and  epithelial  cells,  whose  formation  re- 
quires a  regular  supply  of  nutriment;  and  only  a  part  of  this  nutriment 
(that  which  occupies  the  cavity  of  the  cells)  consists  of  matter,  that  is 


SOURCES   OF  DEMAND   FOR  FOOD.  239 

destined  to  serve  some  other  purpose  in  the  system,  or  that  has  already 
answered  it ;  the  remainder  (that  of  which  the  solid  walls  are  composed) 
being  furnished  by  the  nutritive  materials  of  the  blood,  and  being 
henceforth  altogether  lost  to  it. — Thus  every  act  of  Nutrition  involves 
a  waste  or  decay  of  Organized  tissue. 

412.  We  may  observe  a  marked  difference,  however,  between  the 
amount  of  aliment  required,  and  the  amount  of  waste  occasioned,  by  the 
simple  exercise  of  the  nutritive  or  vegetative  functions  in  the  building- 
up  and  maintenance  of  the  animal  body,  and  that  which  results  from 
the  exercise  of  the  animal  functions.  The  former  are  carried  on,  with 
scarcely  any  intermixture  of  the  latter,  during  foetal  life.  The  aliment, 
in  a  state  of  preparation,  is  introduced  into  the  foetal  vessels ;  and  is 
conveyed  by  them  into  the  various  parts  of  the  structure,  which  are 
developed  at  its  expense.  The  amount  of  waste  is  then  very  trifling,  as 
we  may  judge  by  the  small  amount  of  excretory  matter,  the  product  of 
the  action  of  the  liver  and  kidneys,  which  has  accumulated  at  the  time 
of  birth ;  although  these  organs  have  attained  a  sufficient  development 
to  act  with  energy  when,  called  upon  to  do  so.  But  as  soon  as  the 
movements  of  the  body  begin  to  take  place  with  activity,  the  waste  in- 
creases greatly;  and  we  even  observe  this  immediately  after  birth,  when 
a  large  part  of  the  time  is  still  passed  in  sleep,  but  when  the  actions  of 
respiration  involve  a  constant  employment  of  muscular  power. — In  the 
state  of  profound  sleep,  at  subsequent  periods  of  life,  the  vegetative 
functions  are  performed,  with  no  other  exercise  of  the  animal  powers, 
than  is  requisite  to  sustain  them ;  and  we  observe  that  the  waste,  and 
the  demand  for  food,  are  then  diminished  to  a  very  low  point.  This  is 
well  seen  in  many  animals,  which  lead  a  life  of  great  activity  during 
the  warmer  parts  of  the  year,  but  which  pass  the  winter  in  a  state  of 
profound  sleep,  without,  however,  any  considerable  reduction  of  tempe- 
rature ;  the  demand  for  food,  instead  of  being  frequent,  is  only  felt  at 
long  intervals,  and  the  excretions  are  much  reduced  in  amount.  And 
those  animals  which  become  completely  inert,  either  by  the  influence  of 
cold,  or  by  the  drying-up  of  their  tissues,  do  not  suffer  from  the  pro- 
longed deprivation  of  food ;  because  not  only  are  their  animal  functions 
suspended,  but  their  nutritive  operations  also  are  in  complete  abey- 
ance ;  and  the  continual  decomposition  of  their  tissues,  which  would 
otherwise  be  taking  place,  is  checked  by  the  cold  or  desiccation ;  so  that 
the  whole  series  of  changes  which  goes  on  in  their  active  condition,  is 
completely  at  a  stand. 

413.  But  there  is  another  most  important  cause  of  demand  for  food, 
amongst  the  higher  Animals,  which  does  not  exist  either  amongst  the 
lower  Animals,  or  in  the  Vegetable  kingdom.  We  have  seen  (chap,  ii.) 
that  Mammals  and  Birds,  and  to  a  certain  extent  Insects  also,  are 
able  to  sustain  the  heat  of  their  bodies  at  a  fixed  standard,  and  thus 
to  become  independent  of  variations  in  external  temperature.  This 
they  are  enabled  to  do,  as  will  be  explained  hereafter,  by  a  process 
strictly  analogous  to  ordinary  combustion ;  the  carbon  and  hydrogen 
which  are  directly  supplied  by  their  food,  or  which  have  been  employed 
for  a  time  in  the  composition  of  the  living  tissues  and  are  then  set  free, 
being  made  to  unite  with  oxygen  introduced  by  the  respiratory  process, 


240  OF  FOOD  AND   THE  DIGESTIVE   PROCESS. 

and  thus  giving  off  as  much  heat  as  if  the  same  materials  were  burned 
in  a  furnace.  And  it  has  been  further  shown,  that  the  immediate  cause 
of  death  in  a  warm-blooded  animal,  from  which  food  has  been  entirely 
withheld,  is  the  inability  any  longer  to  sustain  the  temperature,  which 
is  requisite  for  the  performance  of  its  vital  operations  (§  117).  Hence 
we  see  the  necessity  for  a  constant  supply  of  aliment,  in  the  case  of 
warm-blooded  animals,  for  this  purpose  alone :  and  the  demand  will 
be  chiefly  regulated  by  the  external  temperature.  When  the  heat  is 
rapidly  carried  off  from  the  surface,  by  the  chilling  influence  of  the 
surrounding  air,  a  much  greater  amount  of  carbon  and  hydrogen  must 
be  consumed  within  the  body,  to  maintain  its  proper  heatj  than  when 
the  air  is  nearly  as  warm  as  the  body  itself;  so  that  a  diet  which  is 
appropriate  to  the  former  circumstances,  is  superfluous  and  injurious 
in  the  latter ;  and  the  food  which  is  amply  sufiicient  in  a  warm  climate, 
is  utterly  destitute  of  power  to  enable  the  body  to  resist  the  influence 
of  severe  cold.  This  is  a  fact  continually  experienced ;  both  in  the 
ordinary  recurrence  of  changes  of  temperature  in  our  own  climate; 
and,  still  more  remarkably,  when  the  same  individual  is  subjected  to 
the  extremes  of  heat  and  cold,  in  successively  visiting  the  tropical  and 
frigid  zones. 

414.  Thus  we  find  that  in  the  Animal  body,  aliment  is  ordinarily 
required  for  four  different  purposes.  Firsts  for  the  original  construc- 
tion or  building-up  of  the  organism.  Second,  to  supply  the  loss  occa- 
sioned by  its  continual  decay,  even  when  in  a  state  of  repose.  Third, 
to  compensate  for  the  waste  occasioned  by  the  active  exercise  of  the 
nervous  and  muscular  systems.  And  Fourth,  to  supply  the  materials 
?or  the  heat-producing  process,  by  which  the  temperature  of  the  body 
is  kept  up. — The  amount  required  for  these  several  purposes  will  vary 
according  to  the  conditions  of  the  body,  as  regards  exercise  or  repose, 
and  external  heat  or  cold.  It  is  also  subject  to  great  variation  with 
difference  of  age. .  During  the  period  of  growth,  it  might  be  anticipated 
that  a  larger  supply  of  food  would  be  required,  than  when  the  full 
stature  has  been  attained ;  but  a  very  small  daily  addition  would  suffice 
in  the  case  of  a  child  or  youth,  to  produce  the  entire  increase  of  a  whole 
year.  Yet  every  one  knows  that  the  child  requires  much  more  food 
than  the  adult,  in  proportion  to  his  comparative  bulk.  This  results  from 
the  much  more  rapid  change  in  the  constituents  of  his  fabric ;  which  is 
evident  from  the  large  proportional  amount  of  his  excretions,  from  the 
quickness  with  which  the  effects  of  illness  or  of  deficiency  of  food  mani- 
fest themselves  in  the  diminution  of  the  bulk  and  firmness  of  the  body, 
from  the  short  duration  of  life  when  food  is  altogether  withheld,  and 
from  the  readiness  with  which  losses  of  substance  by  disease  or  injury 
are  repaired,  when  the  nutritive  processes  are  restored  to  their  full 
activity.  The  converse  of  all  this  holds  good  in  the  aged  person.  The 
excretions  diminish  in  amount,  the  want  of  food  may  be  sustained  for  a 
longer  period,  losses  of  substance  are  but  slowly  repaired,  and  everything 
indicates  that  the  interstitial  changes  are  performed  with  comparative 
slowness ;  and,  accordingly,  the  demand  for  food  is  far  less  in  propor- 
tion to  the  bulk  of  the  body  than  it  is  in  the  adult,  and  may  be  even 
absolutely  less  than  in  the  child  of  a  fourth  of  its  weight. 


INFLUENCE  OF  VARIATIONS  IN  SUPPLY- OF  FOOD.       241 

415.  The  demand  for  food  is  increased  by  any  cause,  which  creates 
an  unusual  drain  or  waste  in  the  system.  Thus  an  extensive  suppu- 
rating action  can  be  sustained  only  by  a  large  supply  of  highly-nutri- 
tious food.  The  mother,  who  has  to  furnish  the  daily  supply  of  milk 
which  constitutes  the  sole  support  of  her  offspring,  needs  an  unusual 
sustenance  for  this  purpose.  And  there  are  states  of  the  system,  in 
which  the  solid  tissues  seem  to  possess  an  unusual  tendency  to  decom- 
position, and  in  which  an  increased  supply  of  aliment  is  therefore  re- 
quired. This  is  the  case,  for  example,  in  diabetes ;  one  of  the  first 
symptoms  of  which  disease  is  the  craving  appetite,  that  seems  as  if  it 
would  never  be  satisfied.  And  there  can  be  no  doubt  that,  putting 
aside  all  the  other  circumstances  that  have  been  alluded  to,  there  is 
much  difference  amongst  individuals,  in  regard  to  the  rapidity  of  the 
changes  which  their  organism  undergoes,  and  the  amount  of  food  re- 
quired for  its  maintenance. 

416.  The  influence  of  the  supply  of  food  upon  the  size  of  the  indivi- 
dual, is  very  evident  in  the  Vegetable  kingdom-;  and  it  is  most  strikingly 
manifested,  when  a  plant  naturally  growing  in  a  poor  dry  soil  is  trans- 
ferred to  a  damp  rich  one,  or  when  we  contrast  two  or  more  individuals 
of  the  same  species,  growing  in  localities  of  opposite  characters.  Thus, 
says  Mr.  Ward,  '^  I  have  gathered,  on  the  chalky  borders  of  a  wood  in 
Kent,  perfect  specimens  in  full  flower  of  Erythrcea  Centaurium  (Com- 
mon Centaury),  not  more  than  half  an  inch  in  height ;  consisting  of  one 
or  two  pairs  of  most  minute  leaves,  with  one  solitary  flower :  these  were 
growing  on  the  bare  chalk.  By  tracing  the  plant  towards  and  in  the 
wood,  I  found  it  gradually  increasing  in  size,  until  its  full  development 
was  attained  in  the  open  parts  of  the  wood,  where  it  became  a  glorious 
plant,  four  or  five  feet  in  elevation,  and  covered  with  hundreds  of  flow- 
ers." On  the  other  hand,  by  starvation^  naturally  or  artificially  induced. 
Plants  may  be  dwarfed,  or  reduced  in  stature  :  thus  the  Dahlia  has  been 
diminished  from  six  feet  to  two ;  the  Spruce  Fur  from  a  lofty  tree  to  a 
pigmy  bush;  and  many  of  the  trees  of  plains  become  more  and  more 
dwarfish  as  they  ascend  mountains,  till  at  length  they  exist  as  mere 
underwood.  Part  of  this  effect,  however,  is  doubtless  to  be  attributed 
to  diminished  temperature ;  which,  as  already  remarked,  concurs  with 
deficiency  of  food  in  producing  inferiority  of  size. 

417.  Variations  in  the  supply  of  food  would  not  appear  to  be  effec- 
tual in  producing  a  corresponding  variety  of  size  in  the  Animal  king- 
dom :  this  is  not,  however,  because  animals  are^  in  any  degree  less 
dependent  than  Plants  upon  a  due  supply  of  food ;  but  because  such  a 
limitation  of  the  supply,  as  would  dwarf  a  Plant  to  any  considerable 
extent,  would  be  fatal  to  the  life  of  an  Animal.  On  the  other  hand, 
an  excess  of  food,  which  (under  favourable  circumstances),  would  pro- 
duce great  increase  in  the  size  of  the  Plant,  would  have  no  correspond- 
ing influence  on  the  Animal ;  for  its  size  appears  to  be  restrained  within 
much  narrower  limits, — its  period  of  growth  being  restricted  to  the  early 
part  of  its  life,  and  the  dimensions  proper  to  the  species  being  rarely 
exceeded  in  any  great  degree.  Even  in  the  case  of  giant  individuals, 
it  does  not  appear  that  the  excess  of  size  is  produced  by  an  over-supply 
of  food ;  but  that  the  larger  supply  of  food  taken  in  is  called  for  by  the 

16 


242  OF  FOOD  AND   THE  DIGESTIVE   PROCESS. 

unusual  wants  of  the  system, — those  wants  being  the  result  of  an  extra- 
ordinary activity  in  the  processes  of  growth,  and  being  traceable  rather 
to  the  properties  inherent  in  the  system,  than  to  any  external  agencies. 
Thus  we  not  unfrequently  hear  of  children,  who  have  attained  an  extra- 
ordinary size  at  the  age  of  a  few  years  ;  and  this  excess  of  size  is  usually 
accompanied  with  other  marks  of  precocious  development.  We  shall 
hereafter  see,  that  a  provision  exists  in  the  Digestive  apparatus,  which 
absolutely  prevents  the  reduction  and  preparation  of  the  food,  in  any 
amount  greatly  surpassing  that  which  the  wants  of  the  system  demand 
(§  474)  J  and  it  is  probably  to  this  cause,  in  part,  that  we  are  to  attri- 
bute the  small  degree  of  influence  exerted  by  an  excess  of  food,  in  pro- 
ducing an  increased  development  of  the  Animal  frame. 

418.  The  influence  of  a  diminished  supply  of  food,  in  producing  a 
marked  inferiority  in  the  size  of  Animals,  is  most  eff*ectually  exerted 
during  those  early  periods  of  growth,  in  which  the  condition  of  the 
system  is  most  purely  Vegetative.  Thus  it  is  well  known  to  Entomo- 
logists, that,  whilst  it  is  rare  to  find  Insects  departing  widely  from  the 
average  size  on  the  side  of  excess,  dwarf-individuals,  possessing  only 
half  the  usual  dimensions,  or  even  less,  are  not  uncommon;  and  there 
can  be  little  doubt  that  these  have  suffered  from  a  diminished  supply 
of  nutriment  during  their  larva  state.  This  variation  is  most  apt  to 
present  itself  in  the  very  large  species  of  Beetles,  which  pass  several 
years  in  the  larva  state ;  and  such  dwarf  specimens  have  even  been 
ranked  as  sub-species.  Abstinence  has  been  observed  to  produce  the 
effect,  upon  some  Caterpillars,  of  diminishing  the  number  of  moults  and 
accelerating  the  transformation ;  in  such  cases,  the  Chrysalis  is  more 
delicate,  and  the  size  of  the  perfect  Insect  much  below  the  average. 

419.  One  of  the  most  remarkable  examples  known,  of  the  efi*ect  of 
food  in  modifying  the  development  of  Animals,  is  to  be  found  in  the 
economy  of  the  Hive-Bee.  In  every  community,  the  majority  of  indi- 
viduals consists  of  neuters  ;  which  may  be  regarded  as  females,  having 
the  organs  of  the  female  sex  undeveloped ;  and  which,  whilst  incapable 
of  reproduction,  perform  all  the  labours  of  the  hive.  The  office  of  con- 
tinuing the  race  is  restricted  to  the  queen ;  who  is  the  only  perfect 
female  in  the  community.  If  by  any  accident  the  queen  be  destroyed, 
or  if  she  be  purposely  removed  for  the  sake  of  experiment,  the  bees 
choose  two  or  three  from  amongst  the  neuter  larvce,  which  are  being 
nurtured  in  their  appropriate  cells ;  and  these  they  cause  to  be  developed 
into  perfect  queens.  The  first  operation  is  to  change  the  cells  in  which 
they  lie  into  roi/al  cells  ;  these  difl'er  considerably  from  the  ordinary  ones 
in  form,  and  are  of  much  larger  dimensions.  This  is  accomplished  by 
breaking  down  the  w^alls  of  the  surrounding  cells,  removing  the  eggs 
or  grubs  they  may  contain,  and  rebuilding  the  central  cell  upon  an  en- 
larged scale,  and  upon  the  same  plan  as  the  royal  cells  in  which  the 
queens  are  ordinarily  reared.  Whilst  this  operation  is  going  on,  the 
maggot  is  supplied  with  food  of  a  very  diff'erent  nature  from  the  farina 
or  bee-bread  (composed  of  a  mixture  of  pollen  and  honey),  which  has 
been  stored  up  for  the  nourishment  of  the  workers  ;  this  food  being  of  a 
jelly-like  consistence  and  pungent  stimulating  character.  After  the 
usual  transformations,  the  grub  becomes  a  perfect  queen ;  difi'ering  from 


EFFECTS   OF   EXCESS   OF  FOOD.  243 

the  neuter  bee,  into  which  it  would  have  otherwise  been  changed,  not 
only  in  the  development  of  the  reproductive  system,  but  in  the  general 
form  of  the  body,  the  porportionate  shortness  of  the  wings,  the  shape 
of  the  tongue,  jaws,  and  sting,  the  absence  of  the  hollows  on  the  thighs  in 
which  the  pollen  is  carried,  and  the  loss  af  the  power  of  secreting  wax. 

420.  That  insufficiency  of  wholesome  food,  continued  through  succes- 
sive generations,  may  produce  a  marked  effect,  not  merely  upon  the 
stature,  but  upon  the  form  and  condition  of  the  body,  even  in  the 
Human  race,  appears  from  many  cases,  in  which  such  influence  has 
operated  on  an  extensive  scale.  Thus  there  are  parts  of  Ireland  inha- 
bited by  a  population  descended  from  those  who  were  treated  by  the 
English  as  rebels  two  centuries  since,  and  who  were  driven  into  moun- 
tainous tracts,  bordering  on  the  sea,  where  they  have  been  since  exposed 
to  the  two  great  brutalizers  of  the  human  race,  hunger  and  ignorance. 
The  present  race  is  distinguished  physically  from  the  kindred  race  of 
Meath  and  other  neighbouring  districts,  where  the  same  causes  have  not 
been  in  operation,  by  their  low  stature  (not  exceeding  five  feet  two 
inches),  their  pot-bellies  and  bow-legs ;  whilst  their  open  projecting 
mouths,  with  prominent  teeth  and  exposed  gums,  their  advancing  cheek- 
bones and  depressed  noses,  bear  barbarism  in  their  very  front.  "  These 
spectres  of  a  people  that  once  were  well-grown,  able-bodied,  and  comely, 
stalk  abroad  into  the  daylight  of  civilization,  the  annual  apparitions  of 
Irish  ugliness  and  Irish  want." — The  aboriginal  population  of  New 
Holland,  as  a  whole,  presents  a  similar  aspect ;  and  apparently  from 
the  operation  of  the  same  causes. 

421.  When  a  larger  quantity  of  azotized  food  (§  429)  is  habitually 
consumed  than  the  wants  of  the  system  require,  it  is  not  converted  into 
solid  flesh ;  but  it  is  got  rid  of  by  the  various  processes  of  excretion. 
The  increased  production  of  Muscular  fibre  depends,  as  we  have  already 
seen  (§  362),  upon  nothing  so  much  as  the  exercise  of  the  muscle.  It 
cannot  take  place  unless  the  blood  supply  it  with  the  materials ;  but  no 
degree  of  richness  of  the  blood  can  alone  produce  it.  Consequently,  the 
accumulation  of  nutritive  matter  in  the  blood  is  so  far  from  being  a  con- 
dition of  health,  that  it  powerfully  tends  to  produce  disease, — either  of 
an  inflammatory  character,  if  the  fibrine  predominate, — or  of  the  he- 
morrhagic character,  if  the  red  corpuscles  predominate.  This  state  is 
most  apt  to  present  itself  in  those  who  live  well  and  take  little  exercise ; 
and  the  remedy  for  it  is  either  to  diminish  the  diet,  or  to  increase  the 
amount  of  exercise,  so  as  to  bring  the  two  into  ha^rmony. 

422.  The  continued  over-supply  of  food  has  several  injurious  effects : 
it  disorders  the  digestive  processes,  by  stimulating  them  to  undue 
activity,  and  lays  the  foundation  for  a  complete  derangement  of  them ; 
it  gives  a  predisposition  to  the  various  diseases  of  repletion,  as  already 
noticed ;  and  it  throws  upon  the  excreting  organs  much  more  than  their 
proper  amount  of  labour,  besides  tending  to  produce  a  depraved  condi- 
tion of  the  matters  to  be  drawn  off  by  them,  which  renders  the  proper 
act  of  excretion  still  more  difficult.  When  this  is  the  case  various  disor- 
ders arise,  caused  by  the  retention,  within  the  circulating  current,  of 
substances  which  are  very  noxious  to  the  general  system,  and  which 
become  most  fertile  sources  of  disease.     What  are  commonly  regarded 


244  OP  FOOD  AND   THE  DIGESTIVE   PROCESS. 

as  diseases  of  the  biliary  and  urinary  organs,  are  really,  in  a  large  pro- 
portion of  cases,  nothing  else  than  disordered  actions  of  those  organs, 
occasioned  by  the  irregular  mode  in  which  the  products  of  decomposition 
are  formed  within  the  blood,  and  dependent  upon  some  error  in  diet, 
either  as  regards  quantity  or  quality.  Thus  the  "  lithic  acid  diathesis," 
in  which  there  is  an  undue  proportion  of  that  substance  in  the  urine, 
and  of  which  Gout  is  a  particular  manifestation,  is  due,  not  to  disorder 
of  the  kidney,  but  to  an  undue  production  of  lithic  acid  in  the  blood ; 
so  long  as  the  excreting  action  of  the  kidney  is  sufficient  to  prevent  its 
accumulation  in  the  blood,  so  long  the  general  health  is  but  little  affect- 
ed ;  but  whenever  that  action  receives  a  check,  various  constitutional 
symptoms  indicate  that  the  system  is  disturbed  by  the  presence  of  this 
product  of  decomposition.  And  though  our  remedies  may  be  rightly 
directed,  in  part,  to  facilitating  its  escape  through  the  kidneys,  yet  the 
radical  cure  is  to  be  sought  only  in  the  regulation  of  the  diet,  and  in  the 
prevention  of  the  first  production  of  the  substance  in  question. — Similar 
remarks  might  probably  be  applied  to  the  disorders  of  the  Liver ;  but 
we  are,  from  various  causes,  far  less  perfectly  acquainted  with  their 
character  than  we  are  with  those  of  the  Kidney. 

423.  There  is  only  one  tissue,  the  increase  of  which  is  directly  pro- 
duced by  an  over-supply  of  food.  This  is  the  Adipose  or  fatty.  It  is 
formed  almost  entirely  at  the  expense  of  the  non-azotized  constituents 
of  the  food  (§  430) ;  the  walls  of  the  cells,  into  which  the  fatty  matter 
is  secreted,  being  the  only  part  of  this  tissue  that  is  derived  from  the 
proteine-compounds  of  the  blood.  The  production  of  the  adipose  tissue 
is  most  directly  favoured  by  the  presence  of  a  large  amount  of  fatty 
matter  in  the  food ;  but  it  may  also  be  effected,  as  will  be  presently 
shown,  by  the  conversion  of  starchy  and  saccharine  substances  into  fatty 
compounds.  It  cannot  occur,  unless  there  be  in  the  food  a  larger  pro- 
portion of  substances  than  can  be  thus  appropriated,  than  is  sufficient 
to  maintain  the  heat  of  the  system  by  the  respiratory  process.  Conse- 
quently, whatever  increases  the  demand  for  heat  is  unfavourable  to  the 
deposition  of  fat ;  and  vice  versa.  The  fattening  of  animals  is  now 
brought  to  a  regular  system ;  and  experience  has  shown  that  rest  and 
a  warm  temperature,  with  food  containing  a  large  amount  of  oily  mat- 
ter, are  most  conducive  to  the  accumulation.  Rest  acts  by  keeping  the 
respiration  at  a  low  standard ;  for  it  will  hereafter  be  shown  (chap. 
VIII.),  that  a  much  larger  proportion  of  carbonic  acid  is  thrown  off  when 
the  body  is  in  active  movement  than  when  it  is  in  repose.  External 
warmth  has  the  same  effect ;  the  demand  upon  the  calorifyiug  power 
being  diminished,  and  more  of  the  combustible  material  being  left,  to  be 
stored  up  as  fat. 

424.  The  deposition  of  fat  affords  a  supply  of  combustible  matter, 
against  the  time  when  it  may  be  needed ;  and  it  is  consequently  found, 
that  the  duration  of  life  in  warm-blooded  animals,  when  .they  are  com- 
pletely deprived  of  food,  is  in  a  great  degree  proportional  to  the  amount 
of  fat  they  have  previously  accumulated.  There  is  no  sufficient  reason 
to  believe  that  fatty  matter  can  be  converted,  within  the  animal  body, 
into  a  proteine-compound,  which  can  serve  for  the  nutrition  of  the  mus- 
cular and  other  tissues.     But  the  greatest  and  most  constant  waste, 


I 


I 


VALUE   OF   DIFFERENT   MATERIALS    OF   FOOD.  245 

when  an  animal  is  undergoing  starvation,  is  that  which  is  occasioned  by 
the  heat-producing  process ;  this,  so  long  as  the  supply  lasts,  is  kept  up 
by  the  store  of  fat,  which  is  gradually  consumed ;  and  when  it  is  com- 
pletely exhausted  the  temperature  falls,  hour  by  hour,  until  life  can  no 
longer  be  sustained  (§  117).  The  use  of  this  store  of  fat,  in  supplying 
any  temporary  deficiency  in  the  food,  becomes  evident  from  such  expe- 
riments ;  for  when  it  has  been  completely  exhausted,  the  withholding  of 
a  single  meal  proves  fatal,  from  the  want  of  power  to  sustain  the  calori- 
fying  process.  We  find  that  animals,  which  are  likely  to  suffer  from 
deficiency  of  food  in  the  winter,  or  which  spend  that  period  in  a  state 
of  quiescence,  have  a  tendency  to  accumulate  a  store  of  fat  in  the 
autumn ;  which  tendency  seems  principally  to  depend  upon  the  nature 
of  their  food.  We  observe  it  chiefly  in  those  Birds  and  Mammals  which 
live  upon  seeds  and  grains  ;  and  these,  when  ripe,  contain  a  large  quan- 
tity of  oily  matter,  which  thus  becomes  a  valuable  store  against  the  time 
of  need.  There  are  many  birds,  such  as  the  beccafico,  so  much  esteemed 
in  Italy,  which  are  described,  if  killed  at  this  season,  as  being  "  lumps 
of  fat." 

425.  It  is  well  known  to  breeders  of  cattle  that  some  varieties  or 
breeds  have  a  much  greater  tendency  to  the  production  of  Adipose  tis- 
sue than  others  placed  under  the  same  circumstances ;  and  the  former 
are  therefore  selected  to  undergo  the  fattening  process.  Corresponding 
differences  may  be  met  with  among  different  individuals  of  the  Human 
race ;  some  persons  having  a  remarkable  tendency  to  the  production  of 
fat,  under  circumstances  which  do  not  seem  by  any  means  favourable  to 
it,  whilst  others  appear  as  much  indisposed  to  this  deposit.  The  latter 
condition  we  notice  particularly  in  that  temperament  which  is  commonly 
termed  the  "bilious;"  and  it  is  important  to  bear  in  mind  that,  where 
such  an  indisposition  exists,  any  superfluity  of  fatty  matter  in  the  food 
taken  into  the  system,  must  be  excreted  again  through  the  liver,  instead 
of  being  retained  and  stored  up  in  the  body.  It  is  very  desirable, 
therefore,  that  such  persons  should  abstain  from  any  excess  of  this  kind ; 
since  an  habitual  call  upon  the  liver,  to  relieve  the  system  of  a  super- 
fluity of  fatty  matter,  is  certain  to  produce  a  disordered  state  of  that 
organ ;  and  in  order  to  prevent  it,  the  diet  should  be  altered,  so  as  to 
include  less  of  fatty  matter,  or  the  amount  of  exercise  should  be  in- 
creased, so  that  it  may  be  burned  off  by  the  additional  respiration  which 
then  takes  place. 

426.  We  see,  then,  that  the  amount  of  food  y^hich  can  be  properly 
appropriated  by  the  system  varies  considerably  m  different  individuals, 
and  in  the  same  individual  under  different  circumstances.  Consequently 
it  is  impossible  to  give  any  general  rule,  which  shall  apply  to  every  one 
alike.  The  average  quantity  required  by  adult  men,  leading  an  active 
life,  and  exposed  to  the  ordinary  vicissitudes  of  temperature  in  our  own 
climate,  seems  to  be  from  30  to  36  ounces  of  dry  aliment.  ^  But  a 
healthy  condition  may  be  kept  up  on  scarcely  more  than  half  this  allow- 
ance, if  the  muscular  powers  are  but  little  exerted,  and  the  surrounding 
temperature  be  high ;  provided  that  it  consists  of  substances  of  a  nutri- 
tious kind,  united  in  proper  proportions. 

427.  The  value  of  different  substances  as  aliment  depends  in  the  first 


246  OP  FOOD   AND   THE  DIGESTIVE   PROCESS. 

place  upon  the  quantity  of  solid  matter  they  contain ;  being  of  course 
the  greater  as  the  solids  form  the  larger  proportion  of  the  entire  weight. 
Many  esculent  vegetables  contain  so  large  a  quantity  of  water,  that  the 
nutriment  they  afford  is  very  slight  in  proportion  to  their  bulk. — Next 
it  depends  upon  the  proportion  of  digestible  matter  which  the  solid  parts 
include  ;  for  it  is  not  every  substance  containing  the  requisite  ingre- 
dients that  is  capable  of  being  reduced  to  a  state  which  enables  it  to  be 
absorbed.  Thus  woody  fibre  is  composed  of  the  same  elements  as 
starch-gum ;  but  it  passes  out  of  the  intestinal  canal  unchanged,  and 
therefore  affords  no  nutriment.  In  the  same  manner,  the  horny  tissues 
of  animals,  though  nearly  allied  to  proteine  in  their  composition,  are 
completely  destitute  of  nutritive  properties  to  man  and  the  higher  ani- 
mals, because  not  capable  of  being  reduced  by  their  digestive  process ; 
though  certain  insects  appear  capable  of  living  exclusively  upon  them. 

428,  But  when  the  watery  and  indigestible  parts  of  the  food  are  put 
out  of  consideration,  and  our  attention  is  directed  only  to  the  soluble 
solids,  we  find  a  most  important  difference  in  the  chemical  composition 
of  different  substances,  which  renders  them  more  or  less  appropriate  to 
the  different  purposes  which  have  to  be  answered  in  the  nutrition  of  the 
body.  It  has  been  already  pointed  out,  that  Vegetables  possess  the 
power  -of  combining  the  elements  furnished  by  the  inorganic  world  into 
two  classes  of  compounds, — the  ternary,  consisting  of  oxygen,  hydrogen, 
and  carbon, — and  the  quaternary,  which  consist  of  these  elements,  with 
the  addition  of  azote  or  nitrogen.  These  two  classes  are  hence  termed 
the  non-azotized,  and  the  azotized, 

429.  Now  the  azotized  compounds  are  required  for  the  reparation  of 
the  waste  of  the  muscular  tissue,  and  for  the  general  nutrition  of  the 
body;  consequently,  unless  the  food  contain  a  sufficient  proportion  of 
these  substances  the  body  must  be  insufficiently  nourished,  and  the 
strength  must  diminish,  even  though  other  elements  of  the  food  be  in 
superabundance.  The  azotized  substances  formed  by  Plants  are  essen- 
tially the  same,  as  already  shown  (§  174),  with  those  which  are  fur- 
nished by  the  Albuminous  solids  and  fluids  of  Animals ;  but  the  quantity 
of  them  is  usually  small  in  proportion  to  the  non-azotized,  being  consi- 
derable only  in  the  Corn-grains,  in  the  seeds  of  Leguminous  plants,  and 
in  some  other  products,  which  the  universal  experience  of  ages  has 
demonstrated  to  be  the  most  nutritious  of  Vegetable  substances.  The 
other  azotized  compounds  existing  in  the  animal  body  may  be  elaborated 
by  the  transformation  of  these  proteine- compounds ;  so  that  when  they 
are  duly  supplied,  the  system  cannot  become  enfeebled  for  want  of  sup- 
port.— But  there  is  another  azotized  compound,  (jelatine,  that  is  fur- 
nished by  Animals,  to  which  nothing  analogous  exists  in  Plants ;  and 
this,  although  it  cannot  sustain  life  by  itself,  is  a  valuable  adjunct  to  the 
proteine-compounds.  For  as  the  gelatinous  tissues  suffer  waste,  in  com- 
mon with  the  others,  it  is  evident  that  if  the  gelatine  be  supplied  already 
prepared,  it  may  be  at  once  applied  to  their  nutrition  ;  and  thus  the  pro- 
portion of  proteine,  which  they  would  otherwise  require,  is  not  demanded, 
and  the  labour  of  transformation  is  also  saved.  Further,  there  is  this 
great  advantage  in  combining  a  proportion  of  gelatine  with  the  food, — 
especially  when  the  digestive  powers  are  feeble, — that  being  already  in  a 


r 


VALUE   OF  DIFFERENT  MATERIALS   OF  FOOD.  247 

I  Hate  of  perfect  solution,  it  is  taken  up  at  once  by  the  simple  act  of  physir 
cal  absorption  or  endosmose,  instead  of  requiring  any  preliminary  pre- 
paration or  exertion  of  vital  activity  for  its  absorption.  But  there  is  no 
evidence  that  Gelatine  can  ever  be  transformed  into  a  proteine-compound, 
and  can  thus  be  applied  to  the  nutrition  of  the  muscular  and  other  fibrous 
tissues ;  and  the  presumption,  derived  from  the  result  of  various  experi- 
ments, is  very  strong  the  other  way. 

430.  The  Non-azotized  compounds,  which  are  presented  to  us  in  great 
abundance  in  the  Vegetable  kingdom,  exist  under  various  forms ;  of 
which  the  principal  are  starch,  sugar,  and  oil.  The  two  former  may  be 
regarded  as  belonging  to  one  class,  the  Saccharine ;  because  we  know 
that  starch  and  the  substances  allied  to  it  may  be  converted  into  sugar 
by  simple  chemical  processes,  and  that  this  transformation  takes  place 
readily  both  in  the  Vegetable  and  Animal  economy.  On  the  other  hand, 
the  Oily  matters  contained  in  vegetable  and  animal  food,  are  usually 
ranked  as  a  distinct  group  of  alimentary  substances ;  and  it  has  been 
maintained  that,  under  no  circumstances,  has  the  Animal  the  power  of 
elaborating  fatty  matter  from  starchy  or  saccharine  compounds.  But 
this  is  now  known  to  be  an  unfounded  limitation ;  since  the  transforma- 
tion of  a  saccharine  into  a  fatty  compound  takes  place  in  the  case  of 
bees,  which  form  wax  when  fed  upon  pure  sugar,  and  it  has  been  recently 
shown  that  it  may  take  place  in  the  laboratory  of  the  Chemist,  butyric 
acid  (the  fatty  acid  of  butter)  being  one  of  the  products  of  the  fermenta- 
tion of  sugar,  taking  place  under  peculiar  circumstances.  It  appears, 
indeed,  to  be  one  office  of  the  Liver  to  effect  this  transformation,  as  will 
be  explained  hereafter. 

431.  The  great  use  of  these  substances  in  the  Animal  economy,  is  to 
support  the  respiratory  process,  and  thus  maintain  the  temperature  of 
the  body.  We  have  seen  that,  in  the  compounds  of  the  Saccharine  group 
(in  which  Starch  is  included),  the  amount  of  oxygen  is  no  more  than 
sufficient  to  form  water  with  the  hydrogen  of  the  substance  (§  12),  so 
that  the  carbon  is  free  to  combine  with  the  oxygen  taken  in  by  the  lungs, 
and  thus  becomes  a  source  of  calorifying  power.  Again,  in  the  oily 
matters  taken  in  as  food,  the  proportion  of  oxygen  is  far  smaller,  so  that 
they  contain  a  large  quantity  of  surplus  hydrogen,  as  well  as  of  carbon, 
ready  to  be  burned  oft'  in  the  system,  and  thus  to  supply  the  heat  re- 
quired. This  is  obviously  the  ordinary  destination  of  the  alimentary 
matters  belonging  to  these  classes ;  and  the  greatest  economy  in  the 
choice  of  diet  is  therefore  exercised,  when  it  is  composed  of  azotized  sub- 
stances in  sufficient  amount  to  repair  the  waste^  of  the  system,  and  of 
non-azotized  compounds  which  include  free  carbon  and  hydrogen  in  suf- 
ficient quantity  to  develope  (with  the  aid  of  other  processes)  the  requisite 
amount  of  heat  by  combination  with  oxygen.  But  if  there  be  a  deficiency 
in  either  of  these  kinds  of  aliment,  the  body  must  suff"er.  Should  the 
supply  of  duly-prepared  azotized  matter  be  less  than  is  required  to  re- 
pair the  waste  of  the  albuminous  and  gelatinous  tissues,  then  these  di- 
minish in  bulk  and  in  vital  power,  though  the  heat  of  the  body  may  be 
kept  up  to  its  proper  standard.  But  if  the  non-azotized  matter  should 
be  supplied  in  insufficient  amount,  or  in  a  form  in  which  it  cannot  be 
appropriated,  the  heat  of  the  body  cannot  be  sustained  in  any  other  way, 
than  by  drawing  upon  the  store  of  fat  previously  laid  up. 


248  OF   FOOD   AND   THE    DIGESTIVE    PROCESS. 

432.  Various  citcumstances  lead  to  the  belief,  that  the  saccharine 
compounds  are  thus  carried  off  by  the  respiratory  process,  within  a  short 
time  after  they  have  been  introduced  into  the  system.  They  have  not 
been  detected  in  the  chyle  drawn  from  the  lacteal  absorbents  ;  but  there 
seems  reason  to  believe  that,  in  consequence  of  their  ready  solubility, 
they  are  directly  taken  up  by  the  blood  (§  493),  and  that  they  are  so 
rapidly  burned  off  there,  as  to  escape  notice  in  that  fluid.  But  it  has 
been  lately  shown  by  Dr.  Buchanan,  that,  if  the  blood  be  examined 
within  a  short  time  after  a  meal  consisting  in  part  of  farinaceous  and 
saccharine  substances,  a  very  appreciable  quantity  of  saccharine  matter 
is  found  in  it.  This  soon  disappears,  however,  being  eliminated  or  sepa- 
rated from  the  blood  by  the  action  of  the  lungs.  In  fact  it  is  very  pro- 
bable, that  a  large  proportion  of  the  matter  thus  taken  in  never  enters 
the  general  circulation  at  all ;  as  the  blood  of  the  mesenteric  veins  pro- 
ceeds to  the  lungs,  after  passing  through  the  liver,  before  it  is  trans- 
mitted to  the  systemic  arteries,  and  may  there  lose  its  saccharine  matter, 
as  fast  as  this  is  taken  in  from  the  stomach.  After  a  meal  containing  the 
ordinary  admixture  of  saccharine,  oily,  and  albuminous  compounds,  it  is 
probable  that  the  saccharine  are  first  received  into  the  blood,  and  are 
the  first  to  be  eliminated  from  it ;  and  that,  by  the  time  they  have  been 
all  consumed,  the  oily  matter,  introduced  through  the  more  circuitous 
channel  of  the  lacteal  system,  is  ready  to  answer  the  same  purpose.  If 
these  are  exhausted  before  a  fresh  supply  of  food  is  taken  in,  cold  as 
well  as  hunger  is  experienced ;  and  the  body  is  in  this  condition  pecu- 
liarly liable  to  sufi'er  from  any  depressing  causes,  such  as  a  low  external 
temperature,  poisonous  miasmata,  &c. ;  hence  the  prudence  of  avoiding 
exposure  to  such  influences  upon  an  empty  stomach. 

433.  We  can  thus  in  part  account  for  the  fact,  Avhich  universal  expe- 
rience has  established,  that  in  warm-blooded  animals,  a  mixture  of  azo- 
tized  and  non-azotized  substances  is  the  diet  most  conducive  to  the  welfare 
of  the  body ;  and  that,  in  all  but  the  purely  carnivorous  tribes,  the  diet 
provided  by  Nature  consists  not  only  of  albuminous,  gelatinous,  and  oily 
substances,  such  as  are  furnished  by  the  flesh  and  fat  of  animals,  but 
also  of  saccharine  or  farinaceous  matter.  This  is  the  diet  to  which  Man 
is  evidently  best  adapted ;  and  it  is  remarkable  how  completely  accordant 
is  his  use  of  the  ordinary  materials  of  food,  with  the  principles  now  es- 
tablished by  chemical  and  physiological  research,  in  regard  to  the  wants 
of  his  bodily  system,  and  the  best  mode  of  supplying  them.  Thus,  good 
wheaten  bread  contains,  more  nearly  than  any  other  substance  in  ordi- 
nary use,  that  proportion  of  azotized  and  non-azotized  matter,  which 
is  adapted  to  repair  the  waste  of  the  system,  and  to  supply  the  neces- 
sary amount  of  combustible  material,  under  the  ordinary  conditions  of 
civilized  life  in  temperate  climates ;  and  we  find  that  the  health  and 
strength  can  be  more  perfectly  sustained  upon  that  substance,  than  upon 
any  other  taken  alone.  The  addition  of  a  moderate  quantity  of  butter 
increases  its  heat-producing  powers :  and  this  is  especially  useful  when 
the  temperature  is  low,  under  which  condition  there  is  usually  an  in- 
creased disposition  to  the  employment  of  fatty  matters  as  articles  of 
food.  On  the  other  hand,  if  the  body  be  subject  to  violent  exertion, 
advantage  is  gained  by  increasing  the  proportion  of  the  proteine-com- 
pounds,  by  the  addition  of  animal  flesh ;  and,  under  any  circumstances, 


VALUE   OF   DIFFERENT   MATERIALS   OF   FOOD.  249 

there  is  an  economy  in  the  use  of  gelatine,  in  the -form  of  soup,  which 
diminishes  the  demand  for  other  azotized  matter.  The  use  of  animal  flesh, 
however,  as  a  principal  article  of  diet,  except  when  the  individual  is  lead- 
ing the  incessantly-active  life  of  a  carnivorous  animal,  is  very  far  from 
being  economical,  and  is  positively  injurious  to  the  welfare  of  the  body. 

434.  On  the  other  hand,  in  rice,  potatoes,  cassava-meal,  and  similar 
substances,  the  farinaceous  or  saccharine  components  form  so  very  large 
a  proportion  of  the  whole  mass,  and  the  proteine-compounds  are  present  in 
so  very  small  an  amount,  that  they  are  insuflScient  to  support  the  bodily 
vigour  when  taken  alone,  unless  a  larger  quantity  be  ingested,  so  as  to 
supply  the  requisite  proportion  of  azotized  matter.  But  when  these 
substances  form  part  of  a  mixed  diet,  the  other  ingredients  of  which 
consists  of  animal  flesh,  a  much  smaller  quantity  of  them  suffices ;  and 
the  same  kind  of  combination  is  then  formed,  as  exists  in  the  single 
article  of  bread.  Those  in  whose  diet  the  farinaceous  elements  predo- 
minate largely,  and  the  azotized  compounds  exist  in  the  smallest  amount 
compatible  with  the  maintenance  of  the  bodily  vigour,  are  exempt  from 
many  diseases  incident  to  those  who  live  more  highly ;  thus  among  the 
potato-eating  Irish,  and  the  oatmeal-feeding  Scotch,  gout  is  a  disease 
never  heard  of;  whilst  among  the  richer  classes  of  the  same  countries, 
there  is  no  peculiar  exemption  from  it. 

435.  The  oily  constituents  of  food  are  most  abundant  in  the  diet  of 
the  inhabitants  of  frigid  zones,  who  feed  upon  whales,  seals,  and  other 
animals  loaded  with  fat,  and  who  devour  this  fat  with  avidity,  as  if  in- 
stinctively guided  to  its  use.  It  is  by  the  enormous  quantity  of  this 
substance  taken  in  by  them,  that  they  are  enabled  to  pass  a  large  part 
of  the  year  in  a  temperature  below  that  of  our  coldest  winter,  spending 
a  great  portion  of  their  time  in  the  open  air ;  as  well  as  to  sustain  the 
extreme  of  cold,  to  which  they  are  occasionally  subjected.  And  in  con- 
sequence of  its  being  more  slowly  introduced  into  the  system  than  most 
other  substances,  a  larger  quantity  may  be  taken  in  at  one  time,  with- 
out palling  the  appetite ;  whilst  its  bland  and  non-irritating  character 
favours  its  being  retained  until  it  is  all  absorbed.  In  this  manner,  the 
Esquimaux  and  Greenlanders  are  enabled  to  take  in  20  or  30  pounds  of 
blubber  at  a  meal ;  and,  when  thus  supplied,  to  pass  several  day  without 
food.  On  the  other  hand,  among  the  inhabitants  of  warm  climates  there  is 
comparatively  little  disposition  to  the  use  of  oily  matter  as  food ;  and  the 
quantity  of  it  contained  in  most  articles  of  their  diet  is  comparatively  small. 

436.  In  the  Milk,  which  is  the  sole  nutriment  of  young  Mammalia, 
during  the  period  immediately  succeeding  their  bir'th,  we  find  an  admix- 
ture of  albuminous,  saccharine,  and  oleaginous  substances ;  which  in- 
dicates the  intention  of  the  Creator,  that  all  these  should  be  employed 
as  components  of  the  ordinary  diet.  The  Caseine  or  cheesy  matter  is  a 
proteine-compound ;  the  Butyrine  of  butter  is  but  a  slight  modification 
of  its  ordinary  fats  ;  and  its  Sugar  difi'ers  from  that  in  common  use,  only 
by  its  larger  proportion  of  water.  The  relative  amount  of  these  ingre- 
dients in  the  milk  of  diff'erent  animals  is  subject,  as  we  shall  hereafter 
see,  to  considerable  variation ;  but  they  constantly  exist,  at  least  in  the 
milk  of  the  Herbivorous  Mammalia,  and  of  those  which,  like  Man,  sub- 
sist upon  a  mixed  diet.     But  it  has  been  recently  asserted,  that  the  milk 


250  OF  FOOD   AND  THE  DIGESTIVE   PROCESS. 

of  the  purely  Carnivorous  animals  is  destitute  of  Sugar,  consisting,  like 
their  food,  of  proteine-compounds  and  fatty  matter  only. 

437.  No  fact  in  Dietetics  is  better  established,  than  the  impossibility 
of  long  sustaining  health,  or  even  life,  upon  any  single  alimentary  prin- 
ciple. Neither  pure  albumen  or  fibrine,  gelatine  or  gum,  sugar  or  starch, 
oil  or  fat,  taken  alone  for  any  length  of  time,  can  serve  for  the  due  nu- 
trition of  the  body.  This  is  partly  due,  so  far  as  the  non-azotized  com- 
pounds are  concerned,  to  their  incapability  of  supplying  the  waste  of  the 
albuminous  tissues.  This  reason  does  not  apply,  however,  to  the  pro- 
teine-compounds;  which  can  not  only  serve  for  the  reparation  of  the 
body,  but  can  also  afford  the  carbon  and  hydrogen  requisite  for  the  sus- 
tenance of  its  temperature.  The  real  cause  is  to  be  found  in  the  fact, 
that  the  continued  use  of  single  alimentary  substances  excites  such  a 
feeling  of  disgust,  that  the  animals  experimented  on  seem  at  last  to 
prefer  starvation,  rather  than  the  ingestion  of  them.  Consequently  it 
is  quite  impossible  to  ascertain,  by  such  experiments,  the  nutritive  power 
of  the  different  alimentary  principles ;  no  animal  being  capable  of  sus- 
taining life  upon  less  than  two  of  them  at  least.  The  same  disgust  is 
experienced  by  Man,  when  too  long  confined  to  any  article  of  diet,  which 
is  very  simple  in  its  composition ;  and  a  craving  for  change  is  then  ex- 
perienced, which  the  strongest  will  is  scarcely  able  to  resist.  Thus,  in 
the  treatment  of  Diabetes,  a  disease  in  which  there  is  an  undue  tendency 
to  the  production  of  sugar  in  the  system,  it  is  very  important  to  abstain 
completely  from  the  introduction  of  saccharine  or  farinaceous  matters 
in  the  food ;  but  the  craving  for  vegetable  food,  which  is  experienced 
when  the  diet  has  long  consisted  of  meat  alone,  is  such  as  to  make  per- 
severance in  the  latter  very  difficult ;  and  a  means  has  been  latterly 
devised  of  supplying  this  want  without  injury,  by  the  use  of  bread  from 
which  the  starchy  portion  has  been  removed,  the  gluten  or  azotized 
matter  alone  being  eaten.* 

438.  The  organic  compounds,  which  have  been  enumerated  as  sup- 
plying the  various  wants  of  the  system,  would  be  totally  useless  without 
the  admixture  of  certain  inorganic  substances,  which  also  form  a  con- 
stituent part  of  the  bodily  frame,  and  which  are  constantly  being  voided 
by  the  excretions,  especially  in  the  Urine.  These  substances  have 
various  uses  in  the  system.  Thus  common  Salt,  or  the  Chloride  of 
Sodium,  appears  to  afford,  by  its  decomposition,  the  muriatic  acid  which 
is  concerned  in  the  digestive  process,  and  the  soda  which  is  an  important 
constituent  of  the  bile.  Its  presence  in  the  serum  of  the  blood,  also, 
and  in  the  various  animal  fluids  which  are  derived  from  this,  probably 

*  As  an  illustration  of  the  advantage  of  this  treatment,  even  in  unpromising  cases, 
the  author  may  cite  an  instance  which  has  come  under  his  own  observation.  The 
patient  was  a  man  of  72  years  of  age ;  the  disease  had  lasted  at  least  a  year,  and  was 
decidedly  on  the  increase  ;  considerable  loss  of  flesh  and  of  muscular  vigour  had  taken 
place ;  and  the  quantity  of  sugar  in  the  urine  was  such  as  to  make  it  quite  sweet  to  the 
taste.  By  the  careful  restriction  of  his  diet  to  animal  flesh  and  gluten-bread,  this  in- 
dividual kept  the  disease  in  complete  check  for  more  than ^ue  years;  he  gained  flesh, 
and  improved  in  strength  ;  and  his  urine  lost  its  sweetness.  Having  two  or  three  times 
ventured  upon  a  return  to  his  ordinary  diet,  his  old  symptoms  immediately  manifested 
themselves,  warning  him  of  the  necessity  of  perseverance  in  the  strict  regimen  pre- 
scribed for  him.  He  died  at  last,  at  the  age  of  77  years,  of  old  age,  rather  than  of  any 
specific  disease. 


NECESSARY  MAT^IALS_iiE„ANIMAL  FOOD.  251 

aids  in  preventing  the  decomposition  of  the  organic  constituents  of  these 
fimds.— ^Phosphorus  has  been  supposed,  until  recently,  to  be  chiefly  re- 
quisite as  one  of  the  materials  of  the  nervous  tissue  (§  383) ;  and  also, 
when  acidified  by  oxygen,  to  unite  with  lime  in  forming  the  bone-earth 
by  which  bone  is  consolidated.  But  there  is  reason  to  believe,  from  the 
results  of  late  inquiries,  that  the  acid  and  alkaline  phosphate  of  lime  and 
soda  are  very  important  constituents  of  the  various  fluid  secretions,  and 
have  a  large  share  in  their  respective  actions. — Sulphur  exists  in  smalF 
quantities  in  several  animal  tissues ;  but  its  part  appears  to  be  by  no 
means  so  important  as  that  performed  by  Phosphorus. — Lime  is  required 
for  the  consolidation  of  the  bones,  and  for  the  production  of  the  shells 
and  other  hard .  parts  that  form  the  skeletons  of  the  Invertebrata  ;  and 
also  as  the  base  of  the  acid  phosphate,  which  has  been  just  referred  to 
as  an  important  constituent  of  the  animal  fluids. — Lastly,  Iron  is  an 
essential  constituent  of  Haematosine ;  and  is  consequently  required  for 
the  production  of  the  red  corpuscles  of  the  blood  in  Vertebrated  animals, 

439.  These  substances  are  contained,  more  or  less  abundantly,  in" 
most  of  the  articles  generally  used  as  food ;  and  where  they  are  defi- 
cient, the  animal  sufi'ers  in  consequence,  if  they  be  not  supplied  in  any 
other  way.  Thus  common  Salt  exists,  in  no  inconsiderable  amount,  in  the 
flesh  and  fluids  of  animals,  in  the  milk,  and  in  the  substance  of  the  egg ; 
it  is  not  so  abundant,  however,  in  Plants ;  and  the  deficiency  is  usually 
supplied  to  herbivorous  animals  in  some  other  way.  Thus,  salt  is  pur- 
posely mingled  with  the  food  of  domesticated  animals ;  and  in  most 
parts  of  the  world  inhabited  by  wild  cattle,  there  are  spots  where  it 
exists  in  the  soil,  and  to  which  they  resort  to  obtain  it.  Such  are  the 
"  buff'alo-licks"  of  North  America. — Phosphorus  exists  also,  in  combi- 
nation with  proteine-compounds,  in  all  animal  substances  composed  of 
these  ;  and  in  the  state  of  phosphate,  combined  with  lime,  magnesia,  and 
soda,  it  exists  largely  in  many  vegetable  substances  ordinarily  used  as 
food.  The  phosphate  of  lime  is  particularly  abundant  in  the  seeds  of 
the  grasses ;  and  it  also  exists  largely,  in  combination  with  caseine,  in 
Milk. — Sulphur  is  derived  alike  from  vegetable  and  animal  substances. 
It  exists,  in  union  with  proteine-compounds,  in  flesh,  eggs,  and  milk ; 
also  in  several  vegetable  substances ;  and,  in  the  form  of  sulphate  of 
lime,  in  most  of  the  river  and  spring  water  that  we  drink. 

440.  Lime  is  one  of  the  most  universally  diffused  of  all  mineral 
bodies  ;  for  there  are  very  few  Animal  or  Vegetable  substances  in  which 
it  does  not  exist.  The  principal  forms  in  which  it  is  an  element  of  Ani- 
mal nutrition,  are  the  carbonate  and  phosphate.  'Both  these  are  found 
in  the  ashes  of  the  grasses,  and  of  other  plants  used  as  food ;  the  phos- 
phate of  lime  being  particularly  abundant  (as  already  mentioned)  in  the 
corn-grains.  The  production  of  these  cannot  take  place,  to  their  fullest 
extent,  unless  the  soil  previously  contain  phosphate  of  lime  in  a  state  in 
which  the  plant  can  receive  it;  and  it  is  now  understood,  that  the 
diminished  fertility  of  many  lands  is  due,  in  great  part,^  to  the  exhaus- 
tion of  the  soil  as  regards  this  ingredient.  The  restoration  of  the  alka- 
line and  earthy  phosphates  to  the  soil,  in  the  form  of  manure,  is  the 
obvious  means  of  preserving  its  fertility  ;  but  so  long  as  a  very  large 
proportion  of  the  excrements  of  animals  (the  materials  of  which  are 
originally  derived  from  the  earth,  through  the  vegetables  it  supplies)  is 


262  OF   FOOD   AND   THE   DIGESTIVE   PROCESS. 

allowed  to  run  to  waste,  so  long  will  it  be  necessary  that  tlie  requisite 
amount  of  phosphate  of  lime  should  be  drawn  from  foreign  sources. 

441.  The  phosphate  of  lime,  as  already  mentioned,  seems  to  perform 
important  offices  of  a  chemical  nature  in  the  animal  economy,  besides 
being  the  chief  solidifying  ingredient  of  bones  and  teeth  ;  but  the  car- 
bonate would  seem  principally  destined  to  mechanical  uses  only  ;  and 
we  find  it  predominating,  or  existing  as  the  sole  mineral  ingredient,  in 
those  non- vascular  tissues  of  the  Invertebrated  animals,  which  give  sup- 
port  and  protection  to  their  soft  parts  (§  277).  The  degree  of  develop- 
ment of  these  tissues  depends  in  great  part  upon  the  supply  of  carbonate 
of  lime  which  the  animals  receive.  Thus  the  Mollusca  which  inhabit 
the  sea,  find  in  its  waters  the  proportion  of  that  substance  which  they 
require ;  but  those  dwelling  in  streams  and  fresh-water  lakes,  which 
contain  but  a  small  quantity  of  lime,  form  very  thin  shells  ;  whilst  the 
very  same  species  inhabiting  lakes,  which,  from  peculiar  local  causes, 
contain  a  large  impregnation  of  calcareous  matter,  form  shells  of  re- 
markable thickness.  The  Crustacea  which  periodically  throw  off  their 
calcareous  envelope  (§  285),  are  enabled  to  renew  it  with  rapidity  by  a 
very  curious  provision.  There  is  laid  up  in  the  walls  of  their  stomachs 
a  considerable  supply  of  calcareous  matter,  in  the  form  of  little  concre- 
tions, which  are  commonly  known  as  "  crabs'  eyes."  When  the  shell  is 
thrown  off,  this  matter  is  taken  up  by  the  circulating  current,  and  is 
thrown  out  from  the  surface,  mingled  with  the  animal  matter  of  which 
the  shell  is  composed.  This  hardens  in  a  day  or  two,  and  the  new 
covering  is  complete.  Tho  concretions  in  the  stomach  are  then  found 
to  have  disappeared ;  but  they  are  gradually  replaced,  before  the  supply 
of  lime  they  contain  is  again  drawn  upon.  The  large  amount  of  carbo- 
nate of  lime  which  is  required  by  the  laying  Hen,  is  derived  from  chalk, 
mortar,  or  other  substances  containing  it,  which  she  is  compelled  by  her 
instinct  to  eat ;  'and  if  the  supply  of  these  be  withheld,  the  eggs  which 
she  deposits  are  soft  on  their  exterior, — not  being  destitute  of  shell,  as 
commonly  supposed, — but  having  the  fibrous  element  of  the  shell  (§  181) 
unconsolidated  by  the  intervening  deposit  of  chalky  particles. 

2.    Of  the  Digestive  Apparatus j  and  its  Actions  in  general. 

442.  It  has  been  already  pointed  out,  that  the  nature  of  the  food  of 
Animals  is  so  far  different  from  that  of  Plants,  as  to  require  the  prepa- 
ratory process  of  Digestion,  before  its  nutritious  part  can  be  taken  up 
by  the  absorbent  vessels  and  received  into  the  system.  This  process 
may  be  said  to  have  three  different  purposes  in  view :  the  reduction  of 
the  alimentary  matter  to  a  fluid  form,  so  that  it  may  become  capable  of 
absorption  ;  the  separation  of  that  portion  of  it  which  is  fit  to  be  assi- 
milated or  converted  into  organized  texture,  from  that  which  cannot 
serve  this  purpose,  and  which  is  at  once,  rejected ;  and  the  alteration, 
to  a  certain  extent  when  required,  of  the  chemical  constitution  of  the 
former,  which  prepares  it  for  the  important  changes  it  is  subsequently 
to  undergo.  The  simplest  conditions  requisite  for  the  accomplishment 
of  these  purposes  are  the  following  :  a  fluid  capable  of  performing  the 
solution,  and  of  effecting  the  required  chemical  changes  ;  a  fluid  capable 
of  separating  the  excrementitious  matter,  by  a  process  analogous  to 


SIMPLEST  FORMS   OP  DIGESTIVE   APPARATUS.  253 

chemical  precipitation ;  and  a  cavity  or  sac  in  which  these  operations 
may  be  performed. 

443.  In  the  lowest  Animals,  we  find  this  cavity  formed  upon  a  very 
simple  plan  ;  the  digestive  sac  being  a  mere  excavation  in  the  solid  tissue 
of  the  body,  lined  with  a  membrane  which  is  an  inverted  continuation  of 
the  external  integument,  and  communicating  with  the  exterior  by  one 
orifice  only,  through  which  food  is  drawn  in,  and  excrementitious  matter 
rejected.  In  the  little  Hydra,  or  fresh-water  Polype,  the  external 
covering  of  the  body  and  the  lining  of  the  stomach  correspond  so  closely 
in  their  structure,  their  actions  diff'ering  only  with  their  situation,  as  to 
be  mutually  convertible  ;  for  the  animal  may  be  turned  completely  in- 
side-out, without  its  functions  being  deranged:  The  fluid  necessary  to 
dissolve  the  food,  known  by  the  name  of  "gastric  fluid"  or  "gastric 
juice"  is  secreted  in  the  walls  of  the  stomach  ;  and,  from  the  trans- 
parency of  the  tissues,  the  whole  process  may  be  watched.  The  prey 
is  frequently,  and  indeed  generally,  introduced  alive,  by  the  contractile 
power  of  the  arms,  which  coil  round  it,  and  gradually  draw  it  into  the 
mouth  or  entrance  to  the  stomach ;  and  its  movements  may  often  be 
observed  to  continue  for  some  time  after  it  has  been  swallowed.  In  a 
little  time,  however,  its  outline  appears  less  distinct,  and  a  turbid  film 
partly  conceals  it ;  the  soft  parts  are  soon  dissolved  and  reduced  to  a 
fluid  state ;  and  any  firm  indigestible  portions  which  the  body  may  con- 
tain, are  rejected  through  the  aperture  by  which  it  entered.  The  nutri- 
tive matter  is  absorbed  by  the  walls  of  the  stomach,  every  part  of  which 
appears  to  be  endowed  with  equal  power  in  this  respect :  and  it  is  con- 
veyed to  the  remoter  parts  of  the  arms  by  the  simple  imbibition  of  one 
part  from  another,  without  any  proper  circulation  through  vessels. 

444.  In  Polypes  of  a  higher  conformation,  however,  the  digestive 
cavity  is  provided  with  a  second  orifice  :  from  the  dilated  cavity  or 
stomach,  ^n  intestinal  tube  proceeds ;  and  this  has  a  termination  dis- 
tinct from  the  mouth,  though  often  in  its  neighbourhood.  The  food, 
before  entering  the  stomach,  is  submitted  to  a  powerful  triturating  ap- 
paratus, resembling  the  gizzard  of  birds,  by  which  it  is  broken  down ; 
and  in  the  digestive  cavity  it  is  submitted,  not  merely  to  the  action  of 
the  gastric  fluid,  but  also  to  that  of  the  bile,  which  is  secreted  in  little 
follicles  in  the  walls  of  the  stomach,  and  which  is  poured  into  its  cavity 
during  the  process  of  digestion, — being  easily  recognised  by  its  bright 
yellow  colour.  The  excrementitious  matter  is  rejected  in  the  form  of 
little  pellets,  through  the  intestinal  tube.  ^ 

446.  As  we  ascend  the  Animal  scale,  we  find  the  digestive  apparatus 
gradually  increased  in  complexity ;  but  its  essential  characters  remain 
the  same.  Near  the  entrance  to  the  stomach,  we  usually  find  an  appa- 
ratus for  efiecting  the  mechanical  reduction  of  the  food,  by  which  its 
subsequent  solution  may  be  rendered  more  easy.  This  may  consist  of 
a  set  of  teeth ;  either  fixed  in  the  mouth,  as  in  Mammalia  and  Reptiles ; 
or  more  particularly  besetting  the  pharynx,  as  in  Fishes  ;  or  attached 
to  the  walls  of  the  stomach,  as  in  Crustacea.  Or  it  may  be  formed  by 
the  tongue,  converted  into  a  sort  of  rasp  ;  as  in  the  common  Limpet, 
which  thus  reduces  the  sea-weeds  that  constitute  its  chief  food.  Or  the 
same  purpose  may  be  answered  by  a  gizzard,  or  first  stomach,  with  dense 


254  OP  FOOD  AND   THE   DIGESTIVE   PROCESS. 

muscular  and  tendinous  walls  ;  such  as  we  find  in  the  grain-eating  Birds, 
and  many  Insects,  and  in  certain  Molluscs  and  Polypes.  But  where 
the  food  is  already  composed  of  very  minute  particles,  or  is  received  in 
a  liquid  state  (as  in  the  case  of  those  animals  which  live  upon  the  juices 
of  others),  or  is  easily  acted  on  by  the  gastric  juice,  no  such  preparation 
is  requisite. 

446.  Before  the  food  reaches  the  true  digestive  stomach,  it  is  some- 
times delayed  in  a  previous  cavity,  in  order  that  it  may  be  macerated 
in  fluid,  and  may  be  thoroughly  saturated  with  it.  This  is  the  purpose 
of  the  crop  of  Birds,  and  of  the  first  stomach  of  Kuminant  animals. 
When  this  incorporation  with  fluid  is  not  eff*ected  before  the  food  is  sub- 
jected to  the  triturating  process,  it  usually  takes  place  concurrently  with 
it ;  and  in  those  animals  which  reduce  their  food  in  the  mouth  by  the 
process  of  mastication,  there  is  a  special  secretion  of  fluid  into  that 
cavity,  for  this  purpose  ;  this  fluid  is  termed  Saliva,  and  the  act  by 
which  it  is  incorporated  with  the  food  is  termed  insalivation.  The 
mechanical  reduction  of  the  aliment,  and  its  incorporation  with  fluid, 
constitute,  as  we  shall  hereafter  see,  a  very  important  preparation  for 
the  true  digestive  process. 

447.  This  process,  among  the  higher  animals,  takes  place  exclusively, 
or  nearly  so,  in  the  stomach  ;  the  form  of  which  varies  with  the  charac- 
ter of  the  food.  When  this  is  of  a  nature  to  be  easily  acted  on  by 
the  gastric  fluid,  the  stomach  is  a  simple  enlargement  of  the  alimentary 
canal,  almost  in  the  direct  line  between  the  oesophagus  and  the  intestinal 

Fig.  74. 


.  -^  vertical  and  longitudinal  section  of  the  Human  stomach  and  duodenum,  made  in  such  a  direction  as  to 
mclude  tho  two  orifices  of  the  stomach.  1.  The  oesophagus;  upon  its  internal  surface  the  plicated  arrange- 
ment of  the  cuticular  epithelium  is  shown.  2.  The  cardiac  orifice  of  the  stomach,  around  which  the  fringed 
border <)f  the  cuticular  epithelium  is  seen.  3.  The  great  end  of  the  stomach.  4.  Its  lesser  or  pyloric  end. 
5.  The  lesser  curve.  6.  The  greater  curve.  7.  The  dilatation  at  the  lesser  end  of  the  stomach,  which  has 
received  from  Willis  the  name  of  antrum  of  the  pylorus.  This  may  be  regarded  as  the  rudiment  of  a  second 
stomach.  8.  The  rugae  of  the  stomach  formed  by  the  mucous  membrane :  their  longitudinal  direction  is 
shown.  9.  The  pylorus.  10.  The  oblique  portion  of  the  duodenum.  11.  The  descending  portion.  12.  The 
pancreatic  duct  and  the  ductus  communis  choledochus,  close  to  their  termination.  13.  The  papilla  upon 
which  the  ducts  open.  14.  The  transverse  portion  of  the  duodenum.  15.  Thejcommencement  of  the  jeju- 
njim.    In  the  interior  of  the  duodenum  and  jejunum,  the  valvulte  conniventes  are  seen. 

tube ;  so  that  there  is  little  provision  for  the  delay  of  the  food  in  its 
cavity.     But  when  the  aliment  is  such  as  to  be  less  easily  reduced,  and 


1^ 


DIGESTIVE   APPARATUS   OF  MAN.  255 


^  uires  to  be  submitted  to  the  action  of  the  gastric  fluid  for  a  longer 
*^eriod,  the  stomach  forms  a  more  considerable  enlargement,  and  is  placed 
more  out  of  the  direct  line  between  the  oesophagus  and  the  commence- 
ment of  the  intestine.  The  former  condition  obtains  in  the  Carnivora, 
and  particularly  in  those  which  live  more  upon  blood  than  upon  flesh, — 
such  as  Weasels,  Stoats,  &c.,  in  which  this  part  of  the  alimentary  tube 
is  almost  straight ;  the  latter  condition  is  found  among  the  Herbivora, 
and  the  provision  for  the  delay  of  the  aliment  attains  its  greatest  com- 
plexity in  the  Ruminant  animals.  The  •form  of  the  human  stomach 
(Fig.  74)  is  intermediate  between  that  of  purely  carnivorous  and  purely 
herbivorous  animals.  As  in  the  former,  there  is  a  direct  passage  from 
the  cardiac  orifice,  or  entrance  of  the  oesophagus,  to  the  pyloric  orifice, 
or  commencement  of  the  intestine;  but  there  is  also  a  considerable 
dilatation  or  cul  de  sac,  which  is  out  of  that  line ;  and  it  appears  that, 
during  the  digestive  process,  there  is  a  constriction  across  the  stomach, 
which  separates  the  cardiac  portion  from  the  pyloric,  and  causes  the 
retention  of  the  food  in  the  dilated  part  or  large  extremity.  The  gas- 
tric fluid  is  still  secreted  in  the  walls  of  this  organ,  by  scattered  follicles 
which  pour  their  products  into  its  cavity  through  separate  orifices ;  but 
the  bile  is  elaborated  by  a  distinct  organ,  altogether  removed  from  it, 
which  transmits  its  secretion  by  a  single  duct,  that  opens  into  the  intes- 
tinal tube  at  a  short  distance  from  its  commencement ;  and  at  the  same 
point  is  delivered  the  pancreatic  secretion,  which,  as  we  shall  hereafter 
see  (§  480),  takes  an  important  share  in  the  preparation  of  the  alimentary 
products. 

448.  The  action  of  the  Stomach  is  restricted,  in  the  higher  animals, 
to  the  reduction  of  the  food  by  the  solvent  powers  of  the  gastric  juice, 
and  to  the  absorption  (by  the  vessels  in  its  walls)  of  those  parts  of  it 
which  are  in  a  state  of  the  most  perfect  solution.  The  changes  which 
are  produced  by  the  admixture  of  the  biliary  and  pancreatic  fluids  take 
place  in  the  intestine ;  and  the  principal  part  of  the  nutritive  elements 
of  the  food  are  taken  up  by  the  absorbent  vessels  of  the  walls  of  the 
intestine,  after  that  process  has  been  accomplished.  It  would  seem  as 
if  the  preparation  of  the  food  for  absorption  were  not  by  any  means 
completed,  in  this  first  portion  of  the  alimentary  canal ;  for  it  is  still 
destined  to  pass  through  a  long  and  convoluted  tube,  which  is  sometimes 
extended  to  an  extraordinary  degree  ;  and  in  this  passage  it  is  gradually 
exhausted  of  its  nutritious  matter.  The  length  of  the  intestinal  canal 
bears  a  close  relation  to  the  character  of  the  food.^  In  the  Carnivorous 
animals,  whose  aliment  is  easily  dissolved  and  prepared  for  conversion 
into  blood,  the  intestine  is  comparatively  short ;  thus  in  the  Lion  and 
other  Felines  it  is  no  more  than  three  times  the  length  of  the  body ; 
and  in  some  of  the  bloodsucking  Bats,  it  is  almost  straight  and  simple. 
On  the  other  hand,  in  Herbivorous  animals  it  is  of  enormous  length ; 
thus  in  the  Sheep  it  is  about  twenty-eight  times  as  long  as  the  body. 
In  animals  whose  diet  is  mixed,  its  length  is  intermediate  between 
these  extremes  ;  thus  in  Man,  the  whole  length  of  the  intestinal  tube  is 
about  thirty  feet,  or  between  five  and  six  times  that  of  the  body.  The 
intestine  is  of  much  smaller  diameter  along  its  first  portion,  than  it  is 
nearer  its  termination ;  and  it  is  consequently  distinguished  into  the 


256  OF   FOOD   AND   THE   DIGESTIVE   PROCESS. 

small  and  the  large.  In  the  small  intestine,  which  constitutes  in  Man 
about  five-sixths  of  the  whole,  the  surface  of  the  mucous  membrane  is 
greatly  extended  by  the  valvules  conniventes,  which  are  folds  or  dupli- 
catures,  often  several  lines  in  breadth,  not  entirely  surrounding  the 
intestine,  but  extending  for  about  one-half,  or  three-fourths  of  its  cir- 
cumference. These  are  wanting  at  the  lower  part  of  the  ileum.  The 
whole  surface  of  the  mucous  membrane  of  the  small  intestine,  below 
the  entrance  of  the  biliary  ducts,  is  thickly  covered  with  villi,  or  little 
root-like  projections,  in  whiclf  the  proper  absorbent  vessels  originate. 
No  proper  valvulse  conniventes  exist  in  the  large  intestine ;  the  only 
extensions  of  the  mucous  membrane  being  crescentic  folds  at  the  edges 
of  the  sacculi  or  pouch- like  dilatations  in  its  walls ;  and  the  villi  are 
comparatively  few  in  number,  gradually  disappearing  towards  the  termi- 
nation of  the  intestine. 

449.  The  mucous  membrane  of  the  alimentary  canal,  through  its 
whole  course,  is  studded  with  the  orifices  of  numerous  scattered  glands, 
which  lie  in  its  thickness,  or  immediately  beneath  it.  The  simplest  of 
these  are  the  follicles  of  Lieberkiihn,  which  are  small  pouches,  formed 
by  an  inflexion  of  the  mucous  surface,-  analogous  to  the  follicles  of  other 
mucous  membranes  and  apparently  destined  for  the  elaboration  of  the 

protective  secretion  (§  237,  see  Fig.  31,  b).    These 
Fig.  75.  follicles  in  the  small  intestine,  are  very  simple  in 

their  character,  and  not  very  deep ;  and  their 
apertures,  which  are  small,  are  situated  for  the 
most  part  around  the  bases  of  the  villi.  In  the 
large  intestine  they  are  more  prolonged,  especially 

towards  the  extremity  of  the  rectum,  where  they 

Villous  coat  of  Small  In-  form  a  distiuct  layer,  the  component  tubes  of 
*the"?oTHdes"o7tieberS  which  are  visiblc  to  the  naked  eye ;  they  probably 
filled  with  tenacious  white     form  the  peculiarly  thick  and  tenacious  mucus  of 

secretion.  ^  *'  r»  tt  i 

that  part.  Ihese  mucous  follicles  become  parti- 
cularly evident  when  the  membrane  is  inflamed ;  for  they  then  secrete 
an  opaque  whitish  matter,  which  is  absent  in  the  healthy  state,  and 
which  distinguishes  their  orifices  (Fig.  75).  A  modified  kind  of  these 
follicles,  rather  more  complex  in  structure,  is  found  abundantly  in  the 
stomach;  where  it  is  concerned  in  the  secretion  of  the  gastric  fluid 
(§  469). 

450.  The  coats  of  the  intestine  contain  other  glandular,  of  which  some 
appear  destined,  like  the  preceding,  to  elaborate  fluids  of  use  in  the 
system ;  whilst  others  serve  rather  to  draw  ofi"  from  the  blood  certain 
products  of  decomposition,  which  are  to  be  excreted  from  it.  The 
former  are  known  as  the  glands  of  Brunner,  and  the  latter  as  those  of 
Peyer,  after  the  names  of  their  respective  discoverers.  The  glands  of 
Brunner  are  situated  in  the  duodenum,  and  lie,  not  in  the  mucous  but 
in  the  sub-mucous  tissue.  Though  their  size  is  only  about  that  of  a 
hemp-seed,  they  are  of  very  complex  structure,  consisting  of  several 
hundred  follicles,  clustered  round  the  ramifications  of  an  excretory  duct, 
so  as  to  resemble  the  salivary  glands  (Fig.  79);  and  each  pours  its 
secretion  through  a  single  orifice  into  the  intestinal  tube.  Although 
nothing  is  certainly  known  of  the  properties  of  the  fluid  secreted  by  these 


ALIMENTARY   CANAL    AND    ITS   MOVEMENTS.  257 

PjPandulse,  yet  there  is  strong  reason  to  believe,  from  their  position  and 
Bnaracter,  that  it  assists  the  pancreatic  and  biliary  secretions  in  pre- 
paring the  alimentary  materials  for  absorption  (§  480). — The  glands  of 
Peyer  are  either  solitary  or  agminated ;  the  latter 

;    form  large  patches,  which  are  made  of  aggregations  Fig.  76. 

:  of  the  former.  Each  solitary  gland  in  its  closed 
state  consists  of  a  spheroidal  vesicle  (Fig.  76,  a), 
which  is  half  imbedded  in  the  mucous  membrane, 
but  which  also  forms  an  elevated  projection  above 
it ;  and  this  projection  is  surrounded  by  a  ring  or 
zone  of  openings  which  lead  into  an  annular  cluster 
of  Lieberklihnian  follicles.  On  rupturing  one  of 
these  vesicles,  its  cavity  is  found  to  contain  a  gray- 
ish white  matter,  interspersed  with  cells  in  various  Pe^er^ng^andS!  from  the 
stages  of  development ;  and  these  products  appear  to  ^^l^  '^ye%h^^^iZlTl 
be  set  free  by  the  spontaneous  opening  of  the  vesicle,     »?  ^^^^  5°  section,  after  ha' 

•,.,^,'^,  ^,  ',11  1  Ting  opened,  with  the  folh- 

which  takes  place  when  it  has  become  mature,  by  ciesofLieberkuhn  on  either 
the  thinning  away  of  its  wall  at  its  most  projecting  "^*'' 
part  (Fig.  76,  b).  In  any  one  of  the  agminated  glands,  some  of  the 
vesicles  are  usually  found  to  be  open,  and  others  closed.  The  closed 
condition  is  not,  as  was  once  supposed,  peculiar  to  the  Peyerian  glan- 
diilse ;  since,  as  will  be  shown  hereafter,  it  is  the  general  rule  for 
other  glandular  follicles  in  an  early  stage  of  their  development  to  be 
equally  closed  (§  718).  Of  the  nature  of  the  secretions  of  the  Pey- 
erian glandulae,  nothing  has  been  positively  ascertained ;  but  some 
probable  inferences  from  well-known  facts  will  be  stated  hereafter 
(§  749). 

8.  Movements  of  the  Alimentary  Canal. 

451.  The  food  which  is  conveyed  to  the  mouth,  is  grasped  with  the 
lips,  by  a  muscular  effort,  which  is  voluntary  in  the  adult  under  ordinary 
circumstances,  but  which  may  be  performed  automatically  when  the 
influence  of  the  will  is  withdrawn ;  in  the  infant,  as  among  the  lower 
animals,  the  action  seems  purely  automatic,  the  nipple  of  the  mother 
being  firmly  grasped  by  the  lips  when  introduced  between  them,  even 
after  the  brain  has  been  removed. — By  the  act  of  mastication,  which 
then  succeeds,  the  food  is  triturated  and  mingled  with  the  salivary 
secretion ;  and  is  thus  prepared  for  the  further  process  of  solution,  to 
which  it  is  to  be  subjected  in  the  stomach.  The  degree  of  this  prq)a- 
ration,  and  the  form  of  the  instruments  by  which  it  is  effected,  vary  in 
different  animals,  according  to  the  nature  of  the  food.  In  those  Carni- 
vora  whose  aliment  consists  exclusively  of  flesh,  very  little  mastication 
is  necessary,  because  this  substance  is  very  readily  acted  on  by  the 
gastric  fluid ;  and  we  accordingly  find  the  molar  teeth  raised  into  sharp 
cutting  edges,  and  working  against  each  other  with  a  scissors-like 
action  (the  only  one  permitted  by  the  articulation  of  the  jaw),  so  as 
I  simply  to  divide  the  food.  On  the  other  hand,  in  those  Herbivora 
whose  food  consists  of  tough  vegetable  substances,  such  as  the  leaves  of 
grasses,  or  the  stems  and  roots  of  other  plants,  we  find  the  molar  or 

17 


258  OF  FOOD   AND   THE   DIGESTIVE   PROCESS. 

grinding  teeth  peculiarly  adapted  to  its  reduction ;  their  surface  being 
extended  horizontally,  and  being  kept  continually  rough,  by  the  alter- 
nation of  vertical  plates  of  different  degrees  of  hardness  ;  and  the  lower 
jaw  being  so  connected  -with  the  skull,  that  great  freedom  of  motion  is 
permitted.  In  Man  we  find  an  intermediate  conformation,  as  regards 
both  the  teeth  and  the  articulation  of  the  jaw ;  for  the  molar  teeth 
possess  broad  surfaces  which  are  covered  with  a  continuous  coat  of 
enamel,  but  which  are  raised  into  rounded  tubercles ;  and  the  articula- 
tion of  the  jaw  allows  it  a  degree  of  freedom,  which  is  much  greater 
than  that  possessed  by  the  Carnivora ;  although  inferior  to  that  which 
exists  in  many  Herbivora.  The  whole  apparatus  of  Mastication  is  so 
formed  in  Man,  as  to  lead  to  the  conclusion  that  he  is  destined  to  live 
on  a  mixed  diet,  composed  in  part  of  animal  flesh,  and  in  part  of  vege- 
table substances  that  are  sufficiently  soft  to  be  reduced  by  the  simple 
act  of  crushing,  or  by  the  slight  trituration  for  which  the  molar  teeth 
are  adapted. 

452.  The  mechanical  reduction  of  the  food  by  Mastication,  and  the 
incorporation  of  the  Salivary  secretion  with  its  substance,  constitute  a 
very  important  step  in  the  Digestive  process.  We  shall  hereafter  see 
that  the  operations,  to  which  the  alimentary  matter  is  subjected  in  the 
stomach,  are  of  a  purely  Chemical  nature;  and  this  preparation  is 
exactly  of  the  same  character  as  that,  which  the  Chemist  finds  it 
advantageous  to  make,  w^hen  he  is  operating  on  a  substance  of  difficult 
solution*  For  nothing  is  so  favourable  to  the  action  of  the  solvent,  as 
the  previous  reduction  of  the  matter  to  be  dissolved,  and  its  thorough 
incorporation  with  the  fluid  that  is  to  act  upon  it.  We  shall  hereafter 
see,  that  the  relative  properties  of  the  Saliva  and  of  the  gastric  fluid 
are  such,  that,  by  the  minute  admixture  of  the  food  with  the  former, 
the  latter  finds  access  to  every  particle  of  it.  Hence  the  practice  of 
eating  so  rapidly,  that  Mastication  and  Insalivation  are  insufficiently 
performed,  is  extremely  injurious ;  since  it  throws  more  work  upon  the 
Stomach  than  it  ought  to  perform,  by  rendering  its  solvent  action  more 
difficult.  There  can  be  no  doubt  that,  by  the  prolonged  continuance  of 
it,  a  foundation  is  laid  for  the  distressing  complaint  termed  Dyspepsia, 
or  difficulty  of  digestion ;  and  where  any  form  of  this  complaint  exists, 
too  much  attention  cannot  be  paid  to  the  efficient  reduction  of  the  food 
in  the  mouth. 

453.  When  the  aliment  has  been  sufficiently  triturated,  it  is  con- 
veyed into  the  Pharynx  by  the  act  of  Deglutition  or  swallowing. 
This  act  involves  a  great  many  distinct  movements,  into  a  minute 
description  of  which  we  shall  not  here  enter ;  but  it  is  desirable  that 
its  general  nature  should  be  well  understood.  It  is  one  of  those  most 
purely  reflex  in  its  character  (§  394),  and  is  not  capable  of  being  per- 
formed or  even  controlled  by  a  voluntary  effort.  This  statement  may 
seem  inconsistent  with  the  fact,  that  we  swallow  when  we  will ;  but  it 
is  not  so  in  reality.  The  muscular  movements  which  are  concerned  in 
deglutition,  are  called  forth  by  nerves  that  proceed  from  the  spinal  cord, 
not  from  the  brain ;  these  motor  nerves  are  excited  to  action,  by  the 
contact  of  solid  or  fluid  matters  with  the  mucous  surface  of  the  fauces, 
and  in  no   other  way.     The  impression  produced  by  the  contact  is 


MOVEMENTS   OF   (ESOPHAGUS.  259 

conveyed  to  the  Medulla  Oblongata^  or  that  portion  of  the  spinal  cord 
which  lies  within  the  cranium,  by  afferent  nerves  that  terminate  in 
it ;  and,  in  immediate  respondence  to  that  impression,  a  motor  impulse 
is  transmitted  from  it,  which  calls  the  muscles  into  the  combined  action 
necessary  to  produce  the  movement.  Now  this  contact  also  produces 
a  sensation,  provided  the  brain  be  sound  and  awake,  because  nervous 
fibres  proceed  from  the  mucous  surface  to  the  brain  as  well  as  to  the 
spinal  cord ;  but  this  sensation  is  not  a  necessary  link  in  the  chain  of 
actions,  by  which  the  movement  is  produced ;  for  the  act  of  Deglutition 
takes  place  during  profound  sleep,  when  all  sensation  is  suspended, 
and  it  may  be  excited  even  after  the  brain  has  been  removed.  It 
seems  to  be  voluntary,  under  ordinary  circumstances,  simply  because  it 
is  by  an  act  of  the  will,  that  the  matter  to  be  swallowed  is  carried 
backwards  into  contact  with  the  fauces ;  but  that  it  is  not  so  in  reality, 
is  shown  by  the  fact,  that  when  this  impression  has  once  been  made 
with  sufficient  force,  we  cannot  by  any  effort  of  the  will,  prevent  the 
action.  "VVe  have  a  good  example  of  this  in  the  following  cir^mstance, 
of  no  very  unfrequent  occurrence.  The  tickling  of  the  upper  part  of  the 
fauces  with  a  feather  is  often  practised  to  induce  vomiting ;  but  if  the 
end  of  the  feather  be  carried  too  low  down,  it  excites  the  act  of  degluti- 
tion instead ;  the  feather  is  grasped  by  the  pharynx  and  drawn  down- 
wards ;  and  if  it  be  not  held  tenaciously  between  the  fingers,  it  is  drawn 
from  them  and  carried  downwards  into  the  stomach. 

454.  The  carrying-back  of  the  alimentary  matter,  so  that  it  reaches 
the  fauces  or  upper  part  of  the  pharynx,  is  principally  accomplished  by 
the  tongue ;  when  it  has  passed  the  anterior  palatine  arches,  these  con- 
tract and  close  over  the  tongue,  so  as  to  prevent  the  return  of  the  food 
into  the  mouth;  and  at  the  same  time  the  posterior  palatine  arches 
and  the  uvula  are  so  drawn  together,  as  to  prevent  its  passage  into  the 
posterior  nares.  The  larynx  is  drawn  forw^ards  beneath  the  root  of 
the  tongue,  and  the  epiglottis  is  pressed  down  over  the  rima  glottidis, 
so  that  nothing  can  enter  the  latter,  unless  drawn  towards  it  by  an 
act  of  inspiration.  When  fairly  within  the  pharynx,  the  alimentary 
matter  is  seized  by  the  constrictors  which  enclose  that  part  of  the 
alimentary  tube,  and  is  drawn  downwards  by  them  into  the  oesopha- 
gus, which  is  the  cylindrical  continuation  of  it.  The  continued  action 
of  the  constrictors  serves  to  propel  the  food  along  the  oesophagus ;  their 
movement  being  of  a  reflex  nature,  excited  by  the  contact  of  the 
substance  contained  in  the  tube,  with  its  lining;  membrane,  —  which 
produces  an  impression  that  is  transmitted  to  the  medulla  oblongata, 
and  is  reflected  back  as  a  motor  impulse  to  the  muscles.  We  have 
here  a  distinct  case  of  reflex  action  without  sensation;  for  we  have 
no  consciousness  of  the  ordinary  passage  of  food  down  the  oesophagus, 
unless  it  occasion  pressure  on  the  surrounding  parts  through  its  bulk, 
or  unduly  irritate  the  lining  membrane  by  its  high  or  low  temperature 
or  its  acrid  qualities ;  and  yet  it  may  be  shown  by  experiment,  that  the 
completeness  of  the  nervous  circle  is  requisite  for  the  excitement  of  the 
movement,  which  will  not  take  place  when  it  is  interrupted  either  by 
division  of  the  nerves,  or  by  destruction  or  paralysis  of  the  medulla 
oblongata. 


260  OF  FOOD  AND  THE   DIGESTIVE   PROCESS. 

455.  The  progress  of  the  food  along  the  (Esophagus  is  aided  by 
the  action  of  the  muscular  coat  peculiar  to  it.  This  is  composed  of 
the  non-striated  fibre ;  and,  like  that  of  the  intestinal  canal  further  on, 
it  is  usually  stimulated  to  contraction  by  the  direct  contact  of  the 
stimulus,  and  not  either  by  the  will,  or  by  the  reflex  action  of  the  spinal 
cord.  The  movement  produced  by  it  is  of  the  peristaltic  or  wave-like 
kind ;  the  contractions  being  limited  to  one  portion  of  the  tube,  and 
being  propagated  along  it  from  above  downwards.  This  action  con- 
tinues after  the  division  of  all  the  nerves  supplying  the  oesophagus ; 
and  it  cannot,  therefore,  be  dependent  upon  the  brain  or  spinal  cord. 
It  may  be  observed  to  take  place  in  a  rhythmical  manner  (that  is,  at 
short  and  tolerably  regular  intervals),  whilst  a  meal  is  being  swallowed : 
Kut  as  the  stomach  becomes  full,  the  intervals  are  longer  and  the 
wave-like  contractions  less  frequent.  The  degree  in  which  the  action 
of  the  oesophagus  alone,  without  that  of  the  surrounding  muscles,  is 
capable  of  propelling  the  food  into  the  stomach,  seems  to  vary  in  diffe- 
rent animals.  When  the  latter  are  paralysed  in  the  Dog,  by  section  of 
the  nerves  that  supply  them,  the  food  that  has  entered  the  oesophagus  is 
still  propelled  into  the  stomach ;  but  this  is  not  the  case  in  the  Rab- 
bit, the  action  of  its  oesophageal  fibres  not  being  sufficient  to  carry  the 
food  onwards  to  the  stomach,  though  it  will  expel  it  from  the  divided 
extremity  of  the  tube  when  it  is  cut  across.  The  usual  peristaltic 
movements  of  the  oesophagus  are  reversed  in  Vomiting :  and  this  rever- 
sion has  been  observed,  even  after  the  separation  of  the  stomach  from 
the  oesophagus,  as  a  consequence  of  the  injection  of  tartar  emetic  into 
the  veins. 

456.  At  the  point  where  the  oesophagus  enters  the  Stomach, — the 
cardiac  orifice  of  the  latter, — there  is  a  sort  of  sphincter,  or  circular 
muscle,  which  is  usually  closed.  This  opens  when  there  is  a  sufficient 
pressure  on  it,  made  by  the  accumulated  food  propelled  by  the  move- 
jnents  of  the  oesophagus  above ;  and  it  then  closes  again,  so  as  to  retain 
the  food  in  the  stomach.  The  closure  is  due  to  reflex  action ;  for  when 
the  nerves  supplying  it  are  divided,  the  sphincter  no  longer  contracts, 
and  the  food  regurgitates  into  the  oesophagus.  The  opening  of  the  car- 
diac orifice  is  one  of  the  first  acts  which  takes  place  in  vomiting. 

457.  In  Ruminating  animals,  there  is  a  very  remarkable  conforma- 

Fig.  77. 


Compound  Stomach  of  Sheep :— a,  oesophagus ;  6,  paunch ;  c,  second,  or  honeycomb  stomach  ; 
d,  third  stomach,  or  many-plies;  e,  fourth  stomach  or  reed;  /,  pylorus. 

tion  at  the  lower  end  of  the  oesophagus,  which  is  destined  to  regulate 
the  passage  of  food  into  the  different  compartments  of  the  stomach, 


DIGESTIVE   APPARATUS   OF  KUMINANTS. 


261 


according  as  it  has  been  submitted  to  the  second  mastication,  or  not. 
The  oesophagus  (Fig.  77,  a)  does  not  terminate  at  its  opening  into  the 
first  stomach  or  paunch  {h),  but  it  is  continued  onwards  as  a  deep 
groove  with  two  lips  (Fig.  78):  bj  the  closure  of  these  lips  it  is  made 
to  form  a  tube,  which  serves  to  convey  the  food  onwards  into  the 
third  stomach ;  but  when  they  separate,  the  food  is  allowed  to  pass 
either  into  the  first  or  the  second  stomach.  When  the  food  is  first 
swallowed,  it  undergoes  but  very  little  mastication ;  it  is  consequently 
firm  in  its  consistence,  and  is  brought  down  to  the  termination  of  the 
oesophagus  in  dry  bulky  masses.  These  separate  the  lips  of  the  groove 
or  demi-canal  (Fig.  78,  e,  e\  and  pass  into  the  first  and  second  stomachs. 
After  they  have  been  macerated  in  the  fluids  of  these  cavities,  they  are 
returned  to  the  mouth  by  a  reverse  peristaltic  action  of  the  oesophagus ; 
this  return  takes  place  in  a  very  regular  manner,  the  food  being  shaped 
into  globular  pellets  by  compression  within  a  sort  of  mould  formed  by 

Fig.  78. 


Section  of  part  of  the  Stomach  of  the  Sheep,  to  show  the  demi-canal  of  the  oesophagus;  the  mncous  mem- 
brane is  for  the  most  part  removed,  to  show  the  arrangement  of  the  musjftular  fibres.  At  a  is  seen  the 
tetmination  of  the  oesophageal  tube,  the  cut  edge  of  whose  mucous  membrane  is  shown  at  &.  The  lining  or 
the  first  stomach  is  shown  at  c,  c ;  and  the  mucous  membrane  of  the  second  stomach  is  seen  to  be  raised 
from  the  subjacent  fibres  at  d.  At  e,  e,  the  lips  of  the  demi-canal  are  seen  bounding  the  groove,  at  the 
lower  end  of  which  is  the  entrance  to  the  third  stomach  or  many-plies. 

the  demi-canal,  and  these  pellets  being  conveyed  to  the  mouth  at  regular 
intervals,  apparently  by  a  rhythmical  movement  of  the  oesophagus.  It 
is  then  subjected  to  a  prolonged  mastication  within  the  mouth  (the 
"chewing  of  the  cud"),  by  which  it  is  thoroughly  triturated  and  im- 
pregnated with  saliva ;  after  which  it  is  again  swallowed  in  a  pulpy 
semi-fluid  state.  It  now  passes  along  the  groove  which  forms  the  con- 
tinuation of  the  oesophagus,  without  opening  its  lips ;  and  is  thus  con- 
veyed into  the  third  stomach  (Fig.  77,  d),  whence  it  passes  to  the  fourth 


262  OF   FOOD   AND   THE   DIGESTIVE   PROCESS. 

(e),  in  which  alone  the  true  digestive  process  takes  place.  Now,  that  the 
condition  of  the  food  as  to  bulk  and  solidity  is  the  circumstance  which 
determines  the  opening  or  closure  of  the  lips  of  the  groove,  and  which 
consequently  occasions  its  passage  into  the  first  and  second  stomachs, 
or  into  the  third  and  fourth,  appears  from  the  experiment  of  Flourens ; 
who  found  that  when  the  food,  the  first  time  of  being  swallowed,  was 
artificially  reduced  to  a  soft  and  pulpy  condition,  it  passed  for  the  most  part 
along  the  demi-canal  into  the  third  stomach,  as  if  it  had  been  ruminated, 
— only  a  small  portion  finding  its  way  into  the  first  and  second  stomachs. 
How  far  the  actions  of  this  curious  apparatus  are  dependent  upon  ner- 
vous influence, — or  how  far  they  are  due  to  the  exercise  of  the  contrac- 
tility of  the  muscular  fibre,  directly  excited  by  the  contact  of  the  sub- 
stances with  the  lining  membrane  of  the  tubes  and  cavities, — has  not 
yet  been  clearly  ascertained. 

458.  The  food,  when  introduced  into  the  stomach,  and  submitted  to 
the  solvent  action  of  its  secretions,  is  also  subjected  to  a  peculiar  move- 
ment, which  is  efi'ected  by  the  muscular  walls  of  that  organ.  The  pur- 
pose of  this  motion  is  obviously  to  keep  the  contents  of  the  stomach  in 
that  state  of  constant  agitation,  which  is  most  favourable  to  their 
chemical  solution ;  and  particularly  to  bring  every  portion  of  the  ali- 
mentary matter  into  contact  with  the  walls  of  the  stomach,  so  as  to  be 
subjected  to  the  action  of  the  fluid,  which  is  poured  forth  from  them 
during  the  digestive  process.  The  movement  is  produced  by  the  alter- 
nate shortening  and  relaxation  of  the  various  fasciculi,  which  are  dis- 
posed in  almost  every  direction  throughout  the  muscular  wall  of  the 
stomach ;  and  it  seems  to  produce  a  kind  of  revolution  of  the  contents 
of  the  stomach,  sometimes  in  the  direction  of  its  length,  and  sometimes 
transversely.  Its  result  is  well  shown  in  the  hair-balls,  which  are  occa- 
sionally found  in  the  stomachs  of  animals,  that  have  swallowed  hair 
from  time  to  time  through  licking  their  skins ;  the  component  hairs  not 
being  pressed  together  confusedly,  but  being  worked  together  in  regular 
directions,  and  so  interwoven  that  they  cannot  be  readily  separated. 
As  digestion  proceeds,  the  dissolved  fluid  escapes,  little  by  little,  through 
the  pyloric  orifice,  which  closes  itself  firmly  against  the  passage  of 
solid  bodies ;  and  this  motion  continues  until  the  stomach  is  completely 
emptied ;  when  it  ceases,  until  food  is  again  introduced.  The  bulk  of 
the  alimentary  mass  diminishes  rapidly,  as  the  solvent  process  is  near 
its  eompletion;  and  the  separation  of  the  fluid  product  or  chyme  is 
aided  by  a  peculiar  action  of  the  transverse  fasciculi,  which  surround 
the  stomach  at  about  four  inches  from  its  pyloric  extremity.  These 
shorten  in  such  a  manner,  as  to.  produce  a  sort  of  hour-glass  separation 
between  the  portions  of  the  stomach  on  either  side  of  it ;  and  the  fluid 
solution,  being  received  by  the  pyloric  or  smaller  portion,  is  pumped 
away  through  the  pylorus ;  whilst  the  solid  matter  yet  undissolved  is 
retained  in  the  larger  division. 

459.  The  degree  in  which  these  movements  are  dependent  upon  the 
nervous  system,  or  are  under  its  control  or  direction,  has  not  yet  been 
clearly  ascertained.  Distinct  movements  may  be  excited  in  the  stomach 
of  a  Rabbit,  if  it  be  distended  with  food,  by  irritating  the  par  vagum 
soon  after  the  death  of  the  animal;  these  movements  seem  to  commence 


MOVEMENTS   OF   STOMACH   AND   INTESTINE.  263 

from  the  cardiac  orifice,  and  then  to  spread  themselves  peristaltically 
along  the  walls  of  the  stomach ;  but  no  such  movements  can  be  excited 
if  the  stomach  be  empty.  On  the  other  hand,  there  is  distinct  proof 
that  all  the  movements  necessary  to  digestion  may  take  place  after  the 
section  of  that  nerve  ;  although  the  first  effect  of  the  operation  appears 
to  be  to  suspend  them  completely.  It  is  probable  that  the  movements 
of  the  stomach  are  more  regular  and  energetic  in  Herbivorous  animals, 
whose  food  is  difficult  of  digestion,  than  they  are  in  the  Carnivora, 
whose  aliment  is  dissolved  with  comparative  facility. 

460.  From  the  time  that  the  ingested  matter  enters  the  Intestinal 
tube,  it  is  propelled  onwards  by  the  peristaltic  contractions  of  its  mus- 
cular coat ;  which  are  excited,  independently  of  all  nervous  influence, 
by  the  contact  of  the  aliment,  or  by  that  of  the  secretions  mingled  with 
it  in  its  passage  along  the  canal.  These  last  appear  to  have  an  impor- 
tant effect ;  for  we  find  that,  when  the  bile-duct  is  tied,  so  as  to  prevent 
the  bile  from  entering  the  intestine,  constipation  always  occurs ;  whilst 
an  increase  of  the  biliary  and  other  secretions,  consequent  upon  the 
action  of  mercury  or  upon  any  other  cause,  produces  an  increased 
peristaltic  movement,  and  a  more  rapid  discharge  of  the  excrementitious 
matter.  During  the  passage  of  the  alimentary  matter  along  the  small 
intestine,  as  we  shall  see  hereafter,  a  large  proportion  of  its  fluid  is 
removed,  by  the  absorbent  power  of  the  villi ;  and  the  residue  is  again 
brought,  therefore,  to  a  more  solid  consistence.  This  residue  consists 
in  part  of  those  portions  of  the  aliment,  which  are  not  capable  of  being 
dissolved  or  finely  divided,  so  as  to  be  received  by  the  absorbents;  and 
in  part  of  the  matters  poured  into  the  alimentary  canal,  by  the  various 
glands  that  discharge  their  contents  into  it,  for  the  purpose  of  being 
carried  out  of  the  body.  The  faeces,  which  are  thus  formed,  are  pro- 
pelled through  the  large  intestine,  by  the  continued  peristaltic  action 
of  its  walls,  until  they  arrive  at  the  rectum. 

461.  That  the  ordinary  peristaltic  action  of  the  intestinal  canal  is 
independent  of  nervous  influence,  is  sufficiently  indicated  by  the  fact, 
that  it  will  continue  when  the  tube  is  completely  separated  from  all 
connexion  with  the  nervous  centres ;  as  well  as  by  the  difficulty,  already 
adverted  to  (§  353),  of  exciting  contractions  in  the  muscular  coat  by 
any  stimulation  of  its  nerves.  All  the  nerves  of  the  intestine,  from  its 
commencement  at  the  pyloric  orifice  of  the  stomach  to  its  termination 
at  the  anus,  are  derived  from  the  ganglia  of  the  sympathetic  system ; 
but  there  is  evidence  that  those  which  influenpe  its  movements  are 
really  derived  from  the  spinal  cord  (see  chap,  xii.)  Although  the  will 
has  no  influence  whatever  on  the  peristaltic  movement,  yet  the  emotions 
seem  to  affect  it ;  and  it  is  probably  to  convey  their  influence,  that  the 
intestinal  canal  is  supplied  with  motor  nerves.  It  is  also  furnished  with 
sensory  nerves,  which  form  part  of  the  trunks  of  the  sympathetic 
system,  but  which  really  pass  onwards  to  the  brain ;  these  do  not,  how- 
ever, make  us  conscious  of  the  passage  of  the  alimentary  matter  along 
the  canal,  so  long  as  it  is  in  a  state  of  health ;  but  in  various  diseased 
conditions,  they  give  rise  to  sensations  of  the  most  painful  nature. 

462.  For  the  occasional  discharge  of  the  faeces  from  the  rectum,  and 
for  the  retention  of  them  at  other  times,  we  find  the  outlet  or  anal 


264  OF   FOOD   AND   THE   DIGESTIVE   PROCESS. 

orifice  provided  with  an  additional  muscular  apparatus,  which  is  con- 
nected with  the  spinal  system  of  nerves.  The  act  of  Defecation  is  due 
to  the  pressure  upon  the  contents  of  the  rectum,  which  is  occasioned  by 
the  combined  contraction  of  the  diaphragm  and  the  abdominal  muscles ; 
whilst,  on  the  other  hand,  the  retention  of  the  faeces  is  due  to  the  con- 
tractile power  of  the  sphincter  muscle  which  surrounds  the  anus.  The 
action  of  the  sphincter  ani,  like  that  of  the  sphincter  of  the  cardia,  is  a 
reflex  one ;  dependent  upon  the  connexion  of  the  muscle,  by  exciter  and 
motor  nerves,  with  the  spinal  cord.  If  the  lower  portion  of  the  cord 
be  destroyed,  or  if  the  nerves  be  divided,  the  sphincter  loses  its  con- 
tractile power,  and  becomes  flaccid.  When  in  proper  action,  however, 
its  power  is  suflicient  to  prevent  the  escape  of  the  contents  of  the  rec- 
tum ;  until  the  expulsive  force  becomes  very  strong,  in  consequence 
either  of  the  quantity  of  faeces  which  have  accumulated,  or  the  acridity 
of  their  character.  In  either  case,  the  impression  made  upon  the 
mucous  membrane  of  the  rectum  is  conveyed  to  the  spinal  cord ;  and, 
by  a  reflex  motor  impulse,  the  muscles  of  defecation  are  thrown  into 
combined  action,  the  resistance  of  the  sphincter  is  overcome,  and  the 
faeces  are  expelled.  An  unduly  irritable  state  of  the  mucous  membrane, 
or  a  disordered  state  of  the  excrementitious  matter  (resulting  from  the 
irritating  character  of  the  substances  swallowed,  from  the  acrid  charac- 
ter of  the  secretions  poured  into  the  canal,  or  from  an  unusual  change 
in  the  aliment  during  the  digestive  process),  may  occasion  unduly 
frequent  calls  upon  the  muscles  of  defecation,  which  "the  sphincter  is 
unable  to  resist.  On  the  other  hand,  if  the  progress  of  the  faeces  be 
delayed  in  the  large  intestine,  by  deficient  peristaltic  movement,  they 
accumulate  higher  up,  and  the  act  of  defecation  is  not  excited. 

463.  Although  the  sphincter  ani  on  the  one  hand,  and  the  muscles  of 
defecation  on  the  other,  are  called  into  action  by  the  reflex  power  of  the 
spinal  cord,  and  are  so  far  involuntary  in  their  operation,  yet  they  are 
also  in  some  degree  subject  (in  Man  at  least)  to  the  influence  of  the 
will.  The  resistance  of  the  sphincter  may  be  increased  by  a  voluntary 
effort,  when  it  is  desired  to  retain  the  faeces  in  opposition  to  the  power 
of  the  expulsors ;  and  it  is  only  when  the  latter  operate  with  excessive 
force,  that  they  can  overcome  it.  On  the  other  hand,  the  expulsors 
may  be  called  into  action,  or  may  be  aided,  by  the  will,  when  the  stimu- 
lus to  their  movement  received  through  the  spinal  cord  would  not  other- 
wise be  strong  enough;  and  the  faeces  may  thus  be  evacuated  by  a 
voluntary  effort,  at  a  time  when  they  would  not  otherwise  be  discharged. 

4.    Of  the  Secretions  poured  into  the  Alimentary  Canal,  and  of  Changes 
which  they  effect  in  its  contents. 

464.  The  whole  Mucous  Membrane  of  the  Alimentary  canal,  from 
the  mouth  to  the  anus,  is  covered  during  health  with  that  peculiar  viscid 
secretion,  termed  mucus,  of  which  the  characters  have  been  already 
described  (§  237).  This  is  formed,  partly,  on  the  free  surface  of  the 
membrane  itself,  but  chiefly  in  the  numerous  follicles  or  depressions  by 
which  that  surface  is  increased ;  and  it  appears  destined  for  the  protec- 
tion of  the  delicate  highly  vascular  membrane  from  undue  irritation,  by 


SALIVARY  GLANDS  AND   THEIR   SECRETIONS.  265 

the  contact  of  the  substances  which  are  passing  through  the  alimentary 
tube.  When  these  are  unusually  acrid,  the  secretion  of  mucus  is  auo-- 
mented  in  quantity,  and  is  increased  in  viscidity,  so  as  to  form  an  effec- 
tive sheath  to  the  membrane,  which  would  otherwise  suffer  severely. 
When  this  secretion  is  deficient,  the  membrane  is  irritated  by  the  con- 
tact of  any  but  the  blandest  substances ;  and  the  class  of  remedies 
termed  demulcents  are  useful  in  coating  and  protecting  it. 

465.  During  the  mastication  of  the  food  in  the  mouth,  the  Salivary 
secretion  is  poured  in,  for  the  purpose  of  being  mingled  with  it,  and  of 
rendering  the  act  of  masi;ication  more  easy.  This  secretion  is  formed 
by  three  pairs  of  glands, — the  Parotid,  the  Sub-lingual,  and  the  Sub- 
maxillary ;  these  are  composed  of  minute  follicles, 

whose  diameter  is  about  1-lOOOth  of  an  inch,  con-  ^^g-  79. 

nected  together  by  branches  of  their  duct,  upon 
which  they  are  set  like  grapes  upon  their  stalk, 
surrounded  by  a  plexus  of  blood-vessels,  and  bound 
together  by  areolar  tissue.  Within  the  follicles 
are  the  true  secreting  cells  (§  238) ;  by  whose 
growth  and  development,  the  material  of  the  se- 
cretion is  separated  from  the  blood.  These  sali- 
vary cells  are  often  to  be  recognised  in  the  saliva ; 
they  must  not  however  be  confounded  with  the 
epithelium-cells  of  the  mucous  membrane  of  the 
mouth,  which  are  much  larger.  The  fluid  ob- 
tained from  the  mouth  is   not  pure  saliva ;   for   ^  'i^ob\x\e  of  Parotid  oiand 

,  r»     ii  ii      •,       IP    •  •        T     1         •   1     of  new-born  infant,  filled  With 

the    mucus    OI     the     mouth    itsell    is    mingled    with  mercury,  magnified  50  dia- 

the  secretion  from  the  salivary  glands.  If  the  ™®^^^^' 
proportion  of  the  former  be  considerable,  it  gives  to  the  fluid  of  the 
mouth  an  acid  reaction ;  whilst,  if  the  latter  be  predominant  (which  it 
is  directly  before,  and  during,  the  act  of  eating),  the  fluid  of  the  mouth 
has  an  alkaline  reaction.  It  may  be  sometimes  observed,  that  the 
saliva  of  the  mouth  will  strike  a  blue  colour  with  reddened  litmus- 
paper,  whilst  it  turns  blue  litmus-paper  red ;  thus  showing  the  presence 
both  of  an  acid  and  an  alkali  in  a  state  of  imperfect  neutralization. 

466.  The  solid  matter  of  the  Salivary  secretion  is  about  1  per  cent, 
of  the  whole ;  and  this  consists  in  part  of  animal  principles,  and  in 
part  of  saline  substances.  The  animal  matter  consists  of  osmazome, 
mucus,  and  a  peculiar  substance  termed  ptyaline  or  salivary  matter ; 
which  is  soluble  in  water  and  insoluble  in  alcohol^  and  which  is  yet  dif- 
ferent from  both  albumen  and  gelatine.  This  substance  appears  to 
have  a  decided  effect  in  producing  the  metamorphosis  of  certain  alimen- 
tary substances,  on  which  it  acts  like  a  ferment.  Starch  may  be 
converted  into  sugar,  and  sugar  into  lactic  acid,  by  its  agency  ;  and,  if 
acidified,  it  has  a  certain  solvent  power  for  caseine,  animal  flesh,  and 
other  proteine-compounds.  Its  chemical  nature  has  not  yet  been  pre- 
cisely determined.  The  saline  constituents  of  the  Saliva  are  nearly 
identical  with  those  of  the  blood  ;  the  chlorides  of  sodium  and  potassium 
form  considerably  more  than  half;  and  the  remainder  consists  chiefly 
of  the  tribasic  phosphate  of  soda,  to  which  the  alkaline  reaction  of  the 
fluid  is  due,  with  the  phosphates  of  lime,  magnesia,  and  iron.     It  is  of 


266  OF  FOOD  AND   THE   DIGESTIVE   PROCESS. 

the  earthy  phosphates,  that  the  tartar  which  collects  about  the  teeth  is 
chiefly  composed,  the  particles  of  these  being  held  together  by  about 
20  per  cent,  of  animal  matter ;  and  the  composition  of  the  concretions, 
which  occasionally  obstruct  the  salivary  ducts,  is  nearly  the  same. 

467.  The  quantity  of  Saliva  formed  during  the  twenty-four  hours, 
has  been  estimated  at  from  15  to  20  ounces  ;  but  on  this  point  it  is  im- 
possible to  speak  with  certainty.  The  secretion  is  by  no  means  con- 
stantly flowing ;  indeed  it  is  almost  entirely  suspended,  when  the 
masticator  muscles  and  tongue  are  at  perfect  rest,  unless  it  be  excited 
by  any  mental  cause ;  and  hence  it  is,  that .  the  mouth  becomes  dry 
during  sleep,  if  it  be  not  kept  closed.  The  flow  of  Saliva  takes  place 
just  when  it  is  most  wanted ;  that  is,  when  food  has  been  taken  into  the 
mouth,  and  when  the  operation  of  mastication  is  going  on.  But  it  will 
also  take  place,  especially  in  a  hungry  person,  at  the  sight,  or  even  at 
the  idea,  of  savoury  food ;  as  is  implied  by  the  common  expression  of 
the  "mouthwatering"  for  such  an  object.  The  influence  thus  exercised 
over  it  by  the  emotional  state  of  the  mind,  is  probably  conveyed  to  the 
salivary  glands  by  the  Fifth  pair ;  which  contains  many  of  the  gray  or 
organic  filaments,  and  which  seems  to  take  the  place,  in  the  Head,  of  a 
distinct  sympathetic  system. 

468.  Having  been  conveyed  into  th^  stomach,  the  food  is  submitted 
to  the  action  of  the  Gastric  fluid,  which  is  secreted  in  the  walls  of  that 
organ.  This  fluid  is  not  present  in  the  empty  stomach ;  its  secretion 
being  excited  by  the  presence  of  food,  or  by  the  irritation  of  the  walls 
of  the  organ  by  some  solid  body.  In  the  intervals  between  the  diges- 
tive process,  the  mucous  membrane  is  of  a  light  pink  hue ;  but  it 
becomes  more  turgid  with  blood,  when  the  presence  of  food  calls  for 
the  activity  of  its  secreting  processes.  It  is  of  a  soft  and  velvet-like 
appearance ;  and  it  is  constantly  covered  with  a  very  thin  transparent  vis- 
cid mucus,  which  has  neither  acid  nor  alkaline  reaction.  By  applying 
aliment  or  other  stimulants  to  the  internal  coat  of  the  stomach,  and  by 
observing  the  efi'e'ct  through  a  magnifying  glass,  numerous  minute  pa- 
pillse  can  be  seen  to  erect  themselves  upon  the  mucous  membrane,  so  as 
to  rise  through  the  coating  of  mucus ;  and  from  these  is  poured  forth  a 
pure,  limpid,  colourless,  slightly  viscid  fluid,  having  a  distinctly  acid 
reaction,  which  is  the  Gastric  juice.  This  fluid  is  secreted  by  follicles, 
which  are  lodged  in  the  walls  of  the  stomach,  and  which  closely  resemble 
those  that  elsewhere  secrete  mucus  ;  but  they  are  usually  of  more 
complex  structure,  and  are  more  numerous. 

469.  If  the  Mucous  membrane  of  the  stomach  be  divided  by  a  section 
perpendicular  to  its  walls,  it  is  seen  to  be  made  up,  as  it  were,  of  tubu- 
lar follicles  closely  applied  to  each  other ;  their  blind  extremities  resting 
upon  the  submucous  tissue,  and  their  open  ends  being  directed  towards 
the  cavity  of  the  stomach.  In  some  situations  these  tubuli  are  short 
and  straight ;  in  other  parts  they  are  longer,  and  present  an  appearance 
of  irregular  dilatation  or  partial  convolution  (Fig.  80,  1).  This  is  their 
usual  character,  especially  near  the  cardiac  orifice  of  the  stomach ;  but 
near  the  pyloric  orifice  they  have  a  much  more  complex  structure  (Fig. 
80,  2).  These  tubular  follicles  are  arranged  in  bundles  or  groups,  and 
are  surrounded  and  bound  together  by  a  fine  areolar  membrane ;  and 


GASTRIC   FLUID. 


267 


l^is  also  serves  to  convey  vessels  from  the  submucous  tissue,  'which 
tmify  among  the  follicles,  and  supply  the  materials  for  their,  secretion. 


ra; 


Fig.  80. 


Fig.  81. 


Glandulas  from  the  coats  of  the  Stomach, 
magnified  45  diam. ;— 1,  fcom  the  middle  of  the 
stomach;  2,  from  the  neighbourhood  of  the 
pylorus. 


Portion  of  the  Mu- 
cous membrane  of  the 
Stomach,  showing  the 
entrance  to  its  secreting 
tubes,  in  pits  upon  its 
surface. 


The  number  of  tubuli  in  each  group  is  by  no  means  constant.  The  fol- 
licles do  not,  in  general,  open  directly  upon  the  surface ;  but  into  the 
bottom  of  small  depressions  or  pits,  which  may  be  seen  to  cover  the 
membrane  (Fig.  81).  These  pits  are  more  or  less  circular  in  form ;  and 
are  separated  from  one  another  by  membranous  partitions,  which  vary 
in  depth,  and  sometimes  by  pointed  processes,  which  are  capable  of 
erecting  themselves  in  the  manner  just  described.  The  diameter  of 
these  pits  varies  from  about  1-lOOth  to  l-250th  of  an  inch ;  it  is  always 
greatest  near  the  pylorus.  The  number  of  the  gastric  follicles  opening 
into  each,  is  usually  from  three  to  five ;  but  there  are  sometimes  more. 
470.  The  chemical  composition  of  the  Gastric  fluid  has  been  a  subject 
of  much  discussion,  and  can  scarcely  yet  be  regarded  as  precisely  deter- 
mined ;  possibly  it  may  vary  in  its  nature,  according  to  the  state  of  the 
system,  and  the  kind  of  animal  from  which  it  is  obtained.  In  all  cases, 
however,  this  fluid  appears  to  contain  a  free  acid,  together  with  a  pecu- 
liar organic  compound,  Pepsine,  which  seems  like  albumen  in  a  state  of 
change.  It  is  in  regard  to  the  nature  of  the  free  acid  that  Chemists 
are  most  at  issue.  Muriatic,  phosphoric,  acetic,  lactic,  and  butyric  acids 
have  each  been  detected  in  the  gastric  fluid ;  but  there  are  great  diffi- 
culties in  the  way  of  determining  which  of  these  acids  are  free,  and 
which  are  in  combination.  Thus,  although  it  is  very  easy  to  obtain  free 
muriatic  acid  by  distillation  of  the  gastric  fluid,  y;et  this  is  by  no  means 
an  adequate  proof  of  the  previous  presence  of  the  acid  in  a  free  state ; 
for  it  has  been  found  that  free  lactic  acid  will  decompose  chloride  of 
sodium  at  an  elevated  temperature,  forming  (with  water)  lactate  of  soda 
and  muriatic  acid ;  so  that  the  lactic  may  be  the  free  acid  of  the  gastric 
fluid,  the  muriatic  having  been  formed  during  the  distillation,  at  the 
expense  of  the  chloride  of  sodium,  which  is  a  constituent  of  the  gastric 
fluid.  It  has  been  further  determined,  that  muriatic  and  lactic  acids 
both  possess  a  remarkable  solvent  power  for  albuminous  matters,  when 
assisted  by  pepsine ;  so  that  it  is  probable  that  they  may  replace  one 
another. — The  properties  of  the  organic  compound,  named  Pepsme, 
which  is  peculiar  to  the  gastric  fluid,  have  been  principally  studied  in 


268  OF  FOOD  ANIJ  THE   DIGESTIVE   PROCESS. 

that  form  of  it  obtained  from  the  mucous  membrane  of  the  stomach  of 
the  Pig,  which  bears  a  close  resemblance  to  that  of  Man.  When  this 
membrane  is  digested  in  a  large  quantity  of  warm  water,  it  is  purified 
from  the  various  soluble  substances  it  may  contain ;  but  the  pepsine  is 
not  taken  up,  as  it  is  not  soluble  in  warm  water.  By  continuing  the 
digestion  in  cold  water,  the  pepsine  is  then  extracted  nearly  pure. 
When  this  solution  is  evaporated  to  dryness  there  remains  a  brown, 
grayish,  viscid  mass,  having  the  appearance  of  an  extract,  and  the 
odour  of  glue.  A  similar  substance  may  be  obtained  by  adding  strong 
alcohol  to  a  fresh  solution  of  pepsine  ;  for  the  latter  is  then  precipitated 
in  white  flocks,  which  may  be  collected  on  a  filter,  and  which  produce  a 
gray  compact  mass  when  dried.  Pepsine  enters  into  chemical  combina- 
tion with  many  acids ;  forming  compounds  which  still  redden  litmus- 
paper  ;  and  this  appears  to  be  its  condition  in  the  gastric  juice. 

471.  The  muriate  and  acetate  of  pepsine  possess  a  very  remarkable 
solvent  power  for  albuminous  substances.  A  liquid  which  contains  only 
17  ten-thousandths  of  acetate  of  pepsine,  and  6  drops  of  muriatic  acid 
per  ounce,  possesses  solvent  power  enough  to  dissolve  a  thin  slice  of 
coagulated  albumen,  in  the  course  of  six  or  eight  hours'  digestion.  With 
12  drops  of  muriatic  acid  per  ounce,  the  same  quantity  of  white  of  egg 
is  dissolved  in  two  hours.  A  liquid  which  contains  only  half  a  grain  of 
acetate  of  pepsine,  and  to  which  the  muriatic  acid  and  white  of  Q^^g  are 
alternately  added,  so  long  as  the  latter  is  dissolved,  is  capable  of  taking 
up  210  grains  of  coagulated  white  of  egg,  at  a  temperature  between  95° 
and  104°.  The  same  acid  with  pepsine  dissolves  blood,  fibrine,  meat, 
and  cheese ;  whilst  the  acid  without  the  pepsine  requires  a  very  long 
time  to  do  so  at  ordinary  temperatures.  Very  dilute  muriatic  acid, 
however,  at  the  boiling  point,  dissolves  these  albuminous  substances ; 
and  the  solution  has  the  same  characters,  as  that  which  is  made  by  the 
agency  of  pepsine.  The  horny  tissues,  such  as  the  epidermis,  horn, 
hair,  &c.,  and  the  yellow  fibrous  tissue,  are  not  afi'ected  by  the  acid 
solution  of  pepsine. — It  appears  from  these  experiments,  that  the  acid 
is  the  real  solvent ;  and  that  the  action  of  the  pepsine  is  limited  to  di%- 
posing  the  albuminous  matter  for  solution,  producing  in  it  a  change 
analogous  to  that  which  maybe  efi*ected  by  heat.  Hence  it  maybe 
considered,  like  ptyaline,  as  a  sort  of  ferment ;  its  office  being  to  pro- 
duce a  tendency  to  change,  on  the  substances  on  which  it  acts,  without 
itself  entering  into  new  combinations  with  any  of  their  elements. 

472.  These  experiments  appear  to  afford  an  explanation  of  the  pro- 
perties of  the  gastric  fluid,  as  ascertained  by  direct  experiment  upon  it. 
When  drawn  direct  from  the  human  stomach,  it  is  found  to  possess  the 
power  of  dissolving  various  kinds  of  alimentary  substances,  whilst  these 
are  submitted  to  its  action  at  a  constant  temperature  of  100°  (which  is 
about  that  of  the  stomach),  and  are  frequently  agitated.  The  solution 
appears  to  be  in  all  respects  as  perfect  as  that,  which  naturally  takes 
place  in  the  stomach ;  but  a  longer  time  is  required  to  make  it.  This 
is  easily  accounted  for  by  the  diff"erence  of  the  conditions ;  for  no  ordi- 
nary agitation  can  produce  the  same  effect  with  the  curious  movements 
of  the  stomach  (§  458) ;  fresh  gastric  fluid  is  poured  out,  as  it  is  wanted, 
during  the  natural  process  of  digestion;  and  the  continual  removal  of 


PROPERTIES   OF   PEPSINE   AND   OF   GASTRIC   FLUID.  269 

Pthe  matter  which  has  been  already  dissolved,  by  its  exit  through  the 
pylorus,  is  of  course  favourable  to  the  action  of  the  solvent  upon  the 
remainder.  The  quantity  of  food,  which  a  given  amount  of  gastric  fluid 
can  dissolve,  is  limited ;  precisely  as  in  the  case  of  the  acidulous  solu- 
tion of  pepsine.  The  marked  influence  of  temperature  upon  its  action 
is  shown  by  the  fact,  that  fresh  gastric  fluid  has  scarcely  any  influence 
on  the  matter  submitted  to  it,  when  the  bottle  is  exposed  to  cold  air, 
instead  of  being  kept  at  a  temperature  of  100°.  Hence  the  use  of  a 
large  quantity  of  cold  water  at  meal-times,  or  of  ice  afterwards,  must 
retard  the  digestive  process. 

473.  The  pulpy  substance,  which  is  the  product  of  the  reducing 
action  of  the  gastric  juice,  is  termed  Chyme.  Its  consistence  will  of 
course  vary,  in  some  degree,  with  the  relative  quantity  of  solids  and 
liquids  ingested.  In  general  it  is  grayish,  semifluid,  and  homogeneous ; 
and  possesses  a  slightly  acid  taste,  but  is  otherwise  insipid.  When  the 
food  has  been  of  a  rich  oily  character,  the  Chyme  possesses  a  creamy 
aspect ;  but  when  it  has  contained  a  large  proportion  of  farinaceous 
matter,  it  has  rather  the  appearance  of  gruel.  The  state  in  which  the 
various  alimentary  principles  exist  in  it,  has  not  yet  been  accurately 
determined ;  the  following,  however,  may  be  near  the  truth. — The  Pro- 
teine-compounds,  whether  derived  from  Animal  or  Vegetable  food,  are 
all  reduced  to  a  state  of  solution,  if  the  gastric  digestion  have  been 
properly  performed ;  and  in  this  state,  they  have  all  the  properties  of 
Albumen. — Gelatine  will  be  dissolved  or  not,  according  to  its  previous 
condition ;  if  it  exist  in  a  tissue  from  which  it  cannot  readily  be  ex- 
tracted, it  will  pass  forth  almost  unchanged ;  but  when  ingested  in  a 
state  of  solution,  it  remains  so  ;  and  if  it  have  been  previously  prepared 
for  solution  by  boiling,  its  solution  is  completed  in  the  stomach.  Its 
condition,  however,  is  altered  in  the  process ;  for  it  loses  the  power  of 
gelatinizing,  and  cannot  be  precipitated  by  chlorine ;  so  that  it  cannot 
be  detected  as  such  either  in  the  blood  or  the  chyle  into  which  it  is 
received. — The  Gummy  matters  of  Vegetables  are  dissolved,  when  they 
exist  in  a  soluble  form ;  as  in  the  case  of  pure  gum,  pectine,  and  dex- 
trine or  starch-gum.  It  does  not  appear,  however,  that  any  further 
conversion  of  Starch  is  efiected  by  the  gastric  fluid ;  for  if  no  saliva  be 
admitted  into  the  stomach,  no  sugar  is  generated  there  by  the  meta- 
morphosis of  the  starch  which  it  may  contain.  But  the  continued  intro- 
duction of  the  saliva  ordinarily  occasions  the  continuance  of  the  process, 
although  the  presence  of  the  free  acid  of  the  gastpc  fluid  in  some  degree 
interferes  with  it ;  and  it  is  not  until  this  has  been  neutralized  by  the 
admixture  of  the  biliary  and  pancreatic  secretions,  that  the  metamor- 
phosis of  the  starch  is  actively  renewed.  Any  sugar  that  may  have 
been  taken  in  as  such,  or  that  may  have  been  produced  from  starch  by  the 
converting  power  of  the  saliva,  is  reduced  to  the  state  of  complete  solu- 
tion.— Oily  matters  do  not  appear  to  be  in  any  way  acted  upon,  other- 
wise than  by  being  set  free  by  the  solution  of  the  envelopes  which  may 
have  contained  them  [e.  g.  fat  cells),  and  by  being  dispersed  through 
the  mass ;  their  state  of  division,  however,  does  not  seem  to  be  yet  fine 
enough  to  allow  of  their  absorption. — Most  other  substances,  as  resins, 
woody  fibre,  horny  matter,  yellow  fibrous  tissue,  &c.,  pass  unchanged 


270  OF   FOOD   AND   THE   DIGESTIVE  PROCESS. 

from  the  stomach,  and  undergo  no  subsequent  alteration  in  the  intes- 
tinal canal ;  so  that  they  are  discharged  among  the  faeces  as  completely 
useless. 

474.  We  have  now  to  notice  the  conditions,  under  which  the  Gas- 
tric fluid  is  secreted ;  the  knowledge  of  which  is  of  great  practical  im- 
portance. We  have  seen  that  it  is  not  poured  forth,  except  when  food 
is  introduced  into  the  stomach,  or  when  its  walls  are  irritated  in  some 
other  mode ;  and  there  is  reason  to  believe,  that  it  is  not  previously 
secreted  and  stored  up  in  the  follicles,  but  that  the  act  of  secretion 
itself  is  due  to  the  stimulus  applied  to  the  mucous  membrane.  ^  The 
quantity  of  the  fluid  then  poured  into  the  stomach,  however,  is  not 
regulated  by  the  amount  of  food  ingested,  so  much  as  by  the  wants  of 
the  system ;  and  as  only  a  definite  quantity  of  food  can  be  acted  on  by 
a  given  amount  of  gastric  juice,  any  superfluity  remains  undissolved  for 
some  time, — either  continuing  in  the  stomach  until  a  fresh  supply  of  the 
solvent  is  secreted,  or  passing  into  the  intestinal  canal  in  a  crude  state, 
and  becoming  a  source  of  irritation,  pain,  and-  disease.  The  use  of  a 
small  quantity  of  salt,  pepper,  mustard,  or  other  stimulating  substances, 
appears  to  produce  a  gently  stimulating  effect  upon  the  mucous  mem- 
brane, and  by  causing  an  increased  afflux  of  blood,  to  augment  the 
quantity  of  the  gastric  fluid  poured  forth.  Any  excess  of  these  or  other 
irritants,  however,  produces  a  disordered  condition  of  the  mucous  mem- 
brane, which  is  very  unfavourable  to  the  digestive  process.  It  becomes 
red  and  dry,  with  an  insufficient  secretion  of  mucus ;  the  epithelial 
lining  is  abraded,  so  that  the  mucous  coat  is  left  entirely  bare ;  and 
irregular  circumscribed  patches  of  a  deeper  hue,  sometimes  with  small 
aphthous  crusts,  present  themselves  here  and  there  on  the  walls  of  the 
stomach.  Similar  results  follow  excess  in  eating.  When  these  changes 
are  inconsiderable,  the  appetite  is  not  much  impaired,  the  tongue  does 
not  indicate  disorder,  and  the  digestive  process  may  be  performed ;  but 
if  they  proceed  further,  dryness  of  the  mouth,  thirst,  accelerated  pulse, 
foulness  of  the  tongue,  and  other  symptoms  of  febrile  irritation,  mani- 
fest themselves ;  and  no  gastric  secretion  can  then  be  excited  by  the 
stimulus  of  food.  Similar  results  may  follow  the  excitement  of  the 
emotions ;  and  those  of  a  depressing  nature  seem  especially  to  produce 
a  pale  flaccid  condition  of  the  mucous  membrane,  which  is  equally 
unfavourable  to  the  due  secretion  of  gastric,  fluid. 

475.  That  the  amount  of  the  secretion  is  ordinarily  proportioned  to 
the  wants  of  the  system, — that  the  introduction  of  any  superfluous 
aliment  into  the  stomach  is  not  only  useless  but  injurious,  as  giving  rise 
to  irritation, — that  incipient  disorder  of  the  stomach  may  occur,  render- 
ing it  less  fit  than  usual  for  the  discharge  of  its  important  duties,  without 
manifesting  itself  by  the  condition  of  the  tongue, — that  when  the  tongue 
does  indicate  disorder  of  the  stomach,  such  disorder  is  usually  consider- 
able,— and  that  every  particle  of  food  ingested,  in  such  states  as  prevent 
the  secretion  of  gastric  fluid,  is  a  source  of  fresh  irritation, — are  truths 
which  cannot  be  too  constantly  kept  in  mind.  There  can  be  no  doubt 
that  the  habit  of  taking  more  food  than  the  system  requires,  is  a  very 
prevalent  one ;  and  that  it  is  persevered  in,  because  no  evil  result  stems 
to  follow.     But  when  it  is  borne  in  mind  that  this  habit  must  keep  the 


SECRETION  OF  GASTRIC  FLUID.  271 

stomach  in  a  state  of  continual  irritation,  however  slight,  it  can  scarcely 
be  doubted  that  the  foundation  is  thus  laid  for  future  disorder  of  a  more 
serious  kind.  Two  circumstances  especially  tend  to  maintain  this  prac- 
tice in  adults,  independently  of  the  mere  disposition  to  gratify  the 
palate.  One  is  the  habit  of  eating  the  same  amount  of  food,  as  during 
the  period  of  growth,  when  more  was  required  by  the  system.  The 
other  is  the  custom  of  eating  too  fast ;  and  this  is  injurious, — both  by 
preventing  sufficient  mastication,  and  thus  throwing  on  the  stomach 
more  than  its  proper  duty, — and  also  by  causing  an  over-supply  of  food 
to  be  ingested,  before  there  is  time  for  the  feeling  of  satisfaction  to 
replace  that  of  hunger  (§  486). 

476.  Of  the  Albuminous,  Saccharine,  and  other  matters  dissolved  in 
the  Chyme,  there  is  reason  to  believe  that  part  are  absorbed  through 
the  blood-vessels  so  copiously  distributed  on  the  walls  of  the  stomach 
(§  492).  The  remainder,  with  the  undissolved  matters,  pass  into  the 
duodenum,  where  the  chyme  is  mingled  with  the  biliary  and  pancreatic 
secretions. — The  secretion  of  Bile  is  evidently  a  process  of  the  highest 
importance  in  the  economy ;  as  we  may  judge  alike  from  the  size  of  the 
Liver  and  the  supply  of  blood  it  receives,  and  from  the  rapidly  fatal 
effects  of  its  suspension.  That  a  part  of  it  is  purely  excrementitious, 
and  is  poured  into  the  intestinal  tube  for  the  purpose  of  being  carried 
out  of  the  body,  cannot  be  questioned ;  but  there  is  strong  evidence, 
that  a  part  of  it  is  destined  to  be  absorbed  again,  after  performing  some 
action  of  importance  upon  the  contents  of  the  alimentary  canal. — In 
all  but  the  very  lowest  animals,  we  find  traces  of  a  bile-secreting  appa- 
ratus ;  and  this  is  almost  constantly  situated  in  the  immediate  neigh- 
bourhood of  the  stomach.  In  many  cases,  the  secretion  is  poured  directly 
into  the  cavity  of  that  organ ;  but  in  most,  it  is  conveyed  (as  in  Man) 
into  the  intestinal  tube  near  its  commencei:nent.  Hence  it  seems  clear, 
from  the  disposition  of  the  biliary  apparatus,  that  it  has  a  purpose  to 
serve  in  connexion  with  the  digestive  function,  and  is  not  destined  solely 
for  the  elaboration  of  a  product  which  is  to  be  cast  out  of  the  body; 
since,  if  the  latter  were  the  case,  that  product  would  be  carried  out 
immediately,  like  the  urinary  excretion,  and  would  not  be  discharged 
into  the  alimentary  canal  high  up. — This  conclusion  is  confirmed  by 
experiment ;  for  it  has  been  shown  that,  if  the  bile-duct  be  divided,  and 
be  made  to  discharge  its  contents  externally  through  a  fistulous  orifice 
in  the  walls  of  the  abdomen,  instead  of  into  the  intestinal  canal,  those 
animals  which  survive  the  immediate  effects  of  the  operation,  exhibit 
indications  of  the  imperfect  performance  of  the  digestive  operation.  At 
first  they  eat  much,  but  their  food  does  not  seem  to  impart  to  them  an 
adequate  amount  of  nutrition ;  afterwards  they  lose  their  appetite,  be- 
come thin,  and  usually  die  after  an  interval  of  some  months  passed  in 
this  state.  If,  however,  they  be  allowed  to  lick  the  orifice,  so  as  to 
receive  the  fluid  discharged  from  it  into  their  stomachs,  these  injurious 
results  do  not  follow. — The  observation  of  disease  in  the  human  subject 
leads  to  similar  conclusions ;  for,  when  the  biliary  secretion  is  deficient, 
or  its  flow  into  the  intestine  is  obstructed,  the  digestive  processes  are 
evidently  disordered ;  the  peristaltic  action  of  the  bowels  is  not  duly 
performed ;  the  faeces  are  white  and  clayey ;  and  there  is  an  obvious 


272  OF   FOOD   AND   THE   DIGESTIVE   PROCESS. 

insufficiency  in  the  supply  of  nutriment  prepared  for  the  absorbent 
vessels. 

477.  On  the  other  hand,  that  one  great  object  of  the  secretion  is  to 
withdraw  from  the  Blood  certain  products  of  the  decomposition  of  the 
tissues,  which  would  otherwise  accumulate  in  it,  and  would  be  deleterious 
to  its  character,  is  shown  by  evidence  yet  more  decisive.  We  find  that 
the  action  of  the  Liver  is  constant^  and  not  occasional,  like  that  of  the 
Salivary  and  Gastric  glands ;  and  that,  if  anything  interfere  with  the 
secreting  process,  and  thereby  cause  the  accumulation  of  the  elements 
of  the  bile  in  the  blood,  the  effects  of  their  presence  are  immediately 
manifested  in  the  disorder  of  other  functions,  especially  those  of  the 
nervous  system  (§  399) ;  and  the  continued  suspension  of  the  function 
leads  to  a  fatal  result,  unless  the  elements  of  the  bile  are  drawn  off  (as 
sometimes  happens)  by  the  urinary  organs.  When  the  secreting  action 
of  the  liver  has  once  been  performed,  an  obstruction  to  the  discharge  of 
the  bile  into  the  intestine  does  not  seem  to  be  so  immediately  injurious. 
The  fluid  accumulates,  and  distends  the  bile-ducts  and  the  gall-bladder ; 
and  when  they  are  completely  filled,  part  of  it  is  reabsorbed  into  the 
blood,  apparently  in  a  changed  condition,  since  it  does  not  then  produce 
the  same  injurious  effects,  as  result  from  the  accumulation  of  the  same 
materials,  previously  to  the  action  of  the  Liver  upon  them.  The  colour- 
ing matter  seems  to  be  very  readily  taken  back  into  the  circulating 
system ;  and  is  deposited  by  it  in  almost  every  tissue  of  the  body. 

478.  Although  the  secreting  action  of  the  Liver  is  constant,  yet  the 
discharge  of  bile  into  the  intestine  is  certainly  favoured  by  the  presence 
of  chyme  in  the  latter.  The  purpose  of  the  gall-bladder  is  obviously  to 
permit  the  accumulation  of  bile,  when  it  is  not  wanted  in  the  intestine ; 
and  we  find  it  most  constantly  present  in  those  tribes  of  animals,  which 
live  upon  animal  food,  and  which  therefore  take  their  aliment  at  inter- 
vals ;  whilst  it  is  more  frequently  absent  in  those  herbivorous  animals, 
in  which  the  digestive  process  is  almost  constantly  going  on.  The 
middle  coat  of  the  bile-ducts  is  clearly  muscular,  and  has  a  peristaltic 
action  like  that  of  the  intestinal  canal ;  this  action  may  be  excited  by 
galvanism,  or  by  irritation  of  the  branches  of  the  Sympathetic  nerve, 
by  which  it  is  supplied.  The  mucous  coat  of  the  ductus  choledochus  is 
disposed  in  valvular  folds,  in  such  a  manner  as  to  prevent  the  reflux  of 
the  bile  or  of  the  contents  of  the  intestine ;  and  a  still  further  security 
is  afforded  by  the  valvular  covering  to  the  orifice  of  the  duct,  which  is 
furnished  by  the  mucous  covering  of  the  intestine  itself.  The  flow  of 
bile  into  the  intestine,  when  its  presence  is  needed  there,  is  commonly 
imputed  to  the  pressure  of  the  distended  Duodenum  against  the  gall- 
bladder ;  but  it  is  probable  that  the  contractility  of  the  muscular  coat 
of  the  duct  itself,  which  may  be  excited  either  through  the  sympathetic 
nerve,  or  by  irritation  at  the  orifice  of  the  duct  (as  in  the  case  of  the 
Salivary  glands),  is  the  real  cause  of  the  discharge  of  the  fluid.  It  is 
an  interesting  fact,  which  proves  how  much  the  passage  of  the  Bile  into 
the  Intestine  is  dependent  upon  the  presence  of  aliment  in  the  latter, 
that  the  gall-bladder  is  almost  invariably  found  turgid  in  persons  who 
have  died  of  starvation  ;  the  secretion  having  accumulated,  through  the 
want  of  demand  for  it,  although  there  was  no  obstacle  to  its  exit. 


SECRETION   OF  BILE.  273 

479.  The  composition  of  the  Bile,  and  the  structure  of  the  organ 
which  elaborates  it,  will  be  more  appropriately  considered  hereafter, 
when  the  Secreting  apparatus  generally  is  being  described  (chap,  ix.) 
At  present  we  have  to  inquire  what  is  the  precise  effect  of  its  admixture 
with  the  products  of  digestion,  and  what  is  the  purpose  which  this  ad- 
mixture serves.  In  the  first  place,  it  may  be  stated  that  bili^y  matter 
is  essentially  a  soap,  formed  by  the  union  of  a  fatty  acid  with  a  soda- 
base  ;  and  that  it  serves  the  purpose  of  neutralizing  the  acidity  of  the 
chyme,  which  is  derived  from  the  gastric  juice  ;  the  biliary  acids  falling 
down  as  an  insoluble  precipitate,  when  thus  deprived  of  their  soda. 
Further,  the  bile  shares  with  the  pancreatic  fluid  in  ttat  emulsifying 
power,  by  which  the  fatty  matters  of  the  food  are  reduced  to  a  state  of 
such  fine  division,  as  to  be  rendered  capable  of  being  absorbed ;  and 
thus  it  happens  that  the  introduction  of  these  matters  into  the  system, 
through  the  medium  of  the  lacteal  absorbents  (§494),  does  not  take 
place  until  after  the  chyme  has  been  mingled  with  the  biliary  and  pan- 
creatic secretions.  Again,  it  has  been  asserted  (but  the  fact  has  not 
been  fully  substantiated),  that  the  admixture  of  biliary  matter  produces 
a  conversion  of  saccharine  into  fatty  compounds.  When  fresh  bile  is 
mingled  with  newly-formed  chyme,  in  a  glass  vessel,  the  mixture  sepa- 
rates into  three  distinct  parts ;  a  reddish-brown  sediment  at  the  bottom, 
a  whey-coloured  fluid  in  the  centre,  and  a  creamy  pellicle  at  the  top. 
The  central  stratum  probably  contains  the  albuminous,  gelatinous,  sac- 
charine, and  other  matters  in  a  state  of  solution ;  the  superficial  pellicle 
may  be  looked  upon  as  consisting  chiefly  of  oleaginous  matter  destined 
for  absorption  ;  whilst  the  sediment,  partly  consisting  of  the  unreducible 
portion  of  the  food,  and  partly  of  the  biliary  matter  itself,  is  evidently 
excrementitious. 

480.  The  Pancreatic  secretion  has  a  chemical  constitution  very  ana- 
logous to  that  of  Saliva ;  but  the  peculiar  organic  compound  which  it 
contains,  has  been  found  by  M.  Bernard  to  possess  a  power  of  emulsify- 
ing fatty  matter,  when  mingled  with  it ;  and  there  is  strong  reason  to 
believe  that  the  chief  purpose  of  this  secretion  is  to  effect  such  a  change 
in  the  condition  of  the  oleaginous  constituents  of  the  chyme,  as  may 
prepare  them  for  absorption.  But  further,  the  neutralization  of  the  acid 
of  the  gastric  fluid  now  allows  the  metamorphosis  of  starch  to  be  recom- 
menced ;  and  as  there  is  evidence  that  the  production  of  sugar  continues 
to  take  place  during  the  passage  of  the  chymous  mass  along  the  small 
intestines,  in  animals  whose  food  is  partly  or  completely  vegetable,  the 
pancreatic  fluid,  which  has  been  experimentally  ascertained  to  possess 
this  power,  is  probably  the  chief  agent  by  which  the  conversion  is  effected. 
It  may  be  surmised,  further,  that  the  glandulse  of  Brunner  (§  450)  par- 
ticipate in  the  functions  of  the  Pancreas ;  being,  perhaps,  the  chief 
agents  in  the  elimination  of  that  "succus  entericus,"  which  has  been 
experimentally  found  to  concur  with  the  biliary  and  pancreatic  fluids  in 
the  emulsification  of  fatty  matters. 

481.  During  the  passage  of  the  contents  of  the  Intestine,  now  aug- 
mented by  the  biliary  secretion,  along  the  canal,  the  nutritious  portion 
is  gradually  withdrawn  by  the  absorbent  vessels  on  its  walls ;  and  the 
excrementitious  matter  alone  remains,  increased  in  amount  by  the  pro- 

18 


274  OF  FOOD  AND   THE   DIGESTIVE   PROCESS. 

ducts  of  the  secretion  of  the  Peyerian  and  other  glandulae,  with  which 
the  mucous  lining  of  the  lower  intestines  is  studded.  Many  of  the  lower 
animals  are  furnished,  at  the  part  where  the  small  intestine  enters  the 
large,  with  a  ccecum,  resembling  that  which  in  Man  is  termed  the  vermi- 
form appendage  of  the  caecum,  but  greatly  exceeding  it  in  size.  Some- 
times we  find  two  cseca  instead  of  one ;  and  these  are  much  prolonged, 
so  as  to* form  tubes  of  considerable  length.  It  has  been  ascertained 
that,  in  herbivorous  animals,  a  distinctly  acid  secretion  is  formed  by  the 
caecum,  during  the  digestive  process;  and  there  is  reason  to  believe, 
that  the  food  there  undergoes  a  second  process,  analogous  to  that  to  which 
it  has  been  submitted  in  the  stomach,  and  fitted  to  extract  from  it  any 
undissolved  alimentary  matter  which  it  may  still  contain.  There  is  no 
reason  to  believe,  however,  that  any  such  process  takes  place  in  Man, 
whose  real  caecum  is  rudimentary, — the  part  of  the  intestine  which  has 
received  the  name,  being  merely  the  dila;ted  commencement  of  the  colon. 
The  act  of  Defecation,  by  which  the  excrementitious  matter  is  discharged, 
has  been  already  noticed  (§  462) ;  the  Absorption  of  nutritive  matter 
will  be  treated  of  in  the  succeeding  Chapter. 

f).    Of  Hunger,  Satiety,  and  Thirst. 

482.  The  want  of  solid  aliment  is  indicated  by  the  sensation  of 
Hunger  ;  and  the  deficiency  of  fluid  by  that  of  Thirst.  On  the  other 
hand,  the  presence  of  a  sufficiency  of  food  or  liquid  in  the  stomach  is 
indicated  by  the  sense  of  Satiety.  These  sensations  are  intended  as 
our  guides,  in  regard  to  the  amount  of  aliment  we  take  in.  What  is 
the  real  seat  of  these  sensations,  and  on  what  conditions  do  they  de- 
pend ? 

483.  The  sense  of  Hunger  is  referred  to  the  stomach,  and  seems  im- 
mediately to  depend  upon  a  certain  condition  of  that  organ ;  but  what 
that  condition  is,  has  not  yet  been  precisely  ascertained.  It  is  not  pro- 
duced by  mere  emptiness  of  the  stomach,  as  some  have  supposed ;  for, 
if  the  previous  meal  have  been  sufficient,  the  food  passes  entirely  from 
the  cavity  of  the  stomach,  before  a  renewal  of  the  sensation  is  felt.  It 
cannot  be  due  to  the  action  of  the  gastric  fluid  upon  the  coats  of  the 
stomach  themselves  ;  because  this  fluid  is  not  poured  into  the  stomach, 
except  when  the  production  of  it  is  stimulated  by  the  irritation  of  the 
secreting  follicles.  It  has  been  attributed  to  distention  of  the  gastric 
follicles  by  the  secreted  fluid ;  but  there  is  no.  evidence  that  the  fluid  is 
secreted  before  it  is  wanted ;  and,  moreover,  it  is  well  known  that  mental 
emotion  can  dissipate  in  a  moment  the  keenest  appetite,  and  it  is  diffi- 
cult to  imagine  how  this  can  occasion  the  emptying  of  the  follicles. 
Perhaps  the  most  satisfactory  view  is  that,  which  attributes  the  sense  of 
hunger  to  a  determination  of  blood  to  the  stomach,  preparing  it  for  the 
secretion  of  gastric  fluid ;  since  this  is  quite  adequate  to  account  for  the 
impression  made  upon  the  nerves ;  and  it  accords  with  what  has  just 
been  stated  of  the  influence  of  mental  emotions,  since  we  know  that 
these  have  a  powerful  efi'ect  upon  the  circulation  of  blood  in  the  minute 
vessels  (§  603). 

484.  Although  the  sense  of  Hunger  is  immediately  dependent,  in 


SENSE   OF    HUNGER   AND    SATIETY.  275 

great  part  at  least,  upon  the  condition  of  the  stomach,  yet  it  is  iilso  in- 
:  dicative  of  the  condition  of  the  general  system  ;  being  extremely  strong, 
j  when  the  body  has  undergone  an  unusual  wast€  without  a  due  supply  of 
i  food,  even  though  the  stomach  be  in  a  state  of  distention ;  whilst  it  is 
^  not  experienced,  if,  through  the  general  inactivity  of  the  system,  the 
•  last  supply  has  not  been  exhausted,  even  though  the  stomach  has  been 
ilong  empty.  It  is  well  known  that,  when  food  is  deficient,  the  attempt 
';  to  allay  the  pangs  of  hunger  by  filling  the  stomach  with  non-nutritious 
i  substances,  is  only  temporarily  successful ;  the  feeling  soon  returning 
!  with  increased  violence,  though  it  has  received  a  temporary  check. 
'  The  reason  for  this  >  is  obviously,  that  the  general  system  has  received 
no  satisfaction,  although  the  stomach  has  been  caused  to  secrete  gastric 
fluid  by  the  contact  of  solid  matter  with  its  walls ;  so  that  although  the 
!  state  on  which  hunger  immediately  depends,  has  been  for  a  time  relieved, 
:  this  state  is  soon  renewed,  unless  the  solid  matter  introduced  iiito  the 
j  stomach  be  of  an  alimentary  character,  and  be  dissolved  and  carried 
I  into  the  system. 

i      485.  When  the  food  is  nutritious  in  its  character,  but  of  small  bulk, 

experience  has  shown  the  advantage  of  mixing  it  with  noii-nutritious 

.  substances,  in  order  to  give  it  bulk  and  solidity  ;  for  if  this  be  not  done, 

!  it  does  not  exert  its  due  stimulating  influence  upon  the  stomach ;  the 

:  gastric  juice  is  not  poured  forth  in  proper  quantity ;  and  the  result  is, 

that  neither  is  the  sense  of  hunger  relieved,  nor  are  the  wants  of  the 

body  satisfied.     Thus  the  Kamschatdales  are  in  the  habit  of  mixing 

'  earth  or  sawdust  with  the  train-oil,  on  which  alone  they  are  frequently 

reduced  to  live.     The  Yeddahs  or  wild  hunters  of  Ceylon,  on  the  saihe 

principle,  mingle  the  pounded  fi^bres  of  soft  and  decayed  wood  with  the 

I  honey  on  which  they  feed  when  meat-  is  not  to  be  had ;  and  on  one  of 

>  them  being  asked  the  reason  of  the  practice,  he  replied,  "  I  cannot  tell 

i  you,  but  I  know  that  the  belly  must  be  filled."     It  has  been  found  that 

soups  and  fluid  diet  are  not  more  readily  converted  into  chyme  than 

solid  aliment,  and  are  not  alone  fit  for  the  support  of  the  body  in  health ; 

and  it  is  often  to  be  observed,  in  disordered  states  of  the  stomach,  that 

it  can  retain  a  small  quantity  of  easily  digested  solid  food,  when  a  thin 

broth  would  be  rejected. 

486.  The  sense  of  Satiety  is  the  opposite  of  Hunger ;  and  like  it, 
depends  on  two  sets  of  conditions, — the  state  of  the  stomach,  and  that 
of  the  general  system.  It  is  produced  in  the  first  instance  by  the 
ingestion  of  solid  matter  into  the  stomach,  which  g^ves  rise  to  the  feel- 
ing of  fulness ;  but  this  is  only  a  part  of  the  sensation  which  ought  to 
be  experienced;  and  it  is  only  when  the  act  of  digestion  is  being  duly 
performed,  and  nutritive  matter  is  being  absorbed  into  the  vessels,  that 
the  peculiar  feeling  of  satisfaction  is  excited,  which  indicates  that  the 
wants  of  the  system  at  large  are  being  supplied. — It  has  been  very 
justly  remarked  by  Dr.  Beaumont,  that  the  cessation  of  the  demand 
set  up  by  the  system,  rather  than  the  positive  feeling  of  satiety,  should 
be  the  guide  in  regulating  the  quantity  of  food  taken  into  the  stomach. 
The  sense  of  satiety  is  beyond  the  point  of  healthful  indulgence ;  and  is 
Nature's  earliest  indication  of  an  abuse  and  overburden  of  her  powers 


276  OF  FOOD  AND   THE   DIGESTIVE   PROCESS. 

to  replenish  the  system.  The  proper  intimation  is  the  pleasurable  sen- 
sation which  is  experienced,  when  the  cravings  of  the  appetite  are  first 
allayed ;  since,  if  the  stomach  be  sufficiently  distended  with  wholesome 
food  for  this  to  be  the  case,  it  is  next  to  certain  that  the  digestion  of 
that  food  will  supply  what  is  required  for  the  nutrition  of  the  body.  It 
is  only  when  the  substance  with  which  the  stomach  is  distended,  is  not 
of  a  digestible  character,  that  the  feelings  excited  by  the  state  of  that 
organ  are  anything  but  a  correct  index  of  the  wants  of  the  system. 

487.  The  Par  Vagum  is  evidently  the  nerve,  which  conveys  to  the 
sensorium  the  impression  of  the  state  of  the  stomach,  and  which  is 
therefore  the  immediate  excitor  of  the  sensation  of  hunger,  or  of  the 
feeling  of  satiety.  But  it  is  evident  from  experiments  upon  animals, 
that  it  is  not  the  only  source,  through  which  they  are  incited  to  take 
food,  and  are  informed  when  they  have  ingested  enough ;  and  it  is 
probable  that  the  Sympathetic  nerve  is  the  channel,  through  which  the 
wants  of  the  si/stem  are  made  known,  and  through  which,  in  particular, 
the  feeling  of  general  exhaustion  is  excited,  that  is  experienced  when 
there  has  been  an  unusual  waste,  or  when  the  proper  supply  has  been 
too  long  withheld. 

488.  The  conditions  of  the  sense  of  Thirst  are  very  analogous  to 
those  of  hunger ;  that  is,  it  indicates  the  deficiency  of  fluid  in  the  body 
at  large ;  but  the  immediate  seat  of  the  feeling  is  a  part  of  the  ali- 
mentary canal, — not  the  stomach,  however,  but  the  fauces.  It  is  re- 
lieved by  the  introduction  of  fluid  into  the  circulating  system,  through 
any  channel ;  whilst  the  mere  contact  of  fluids  with  the  surface  to 
which  the  sensation  is  referred,  produces  only  a  temporary  efi"ect,  un- 
less absorption  take  place.  If  liquids  be  introduced  into  the  stomach 
by  an  oesophagus-tube,  they  are  just  as  eff'ectual  in  allaying  thirst,  as 
if  they  were  swallowed  in  the  ordinary  manner ;  and  the  same  result 
follows  the  injection  of  fluid  into  the  veins  (as  was  most  remarkably 
the  case  when  this  method  of  treatment  was  practised  in  the  Asiatic 
Cholera),  or  the  absorption  of  fluid  through  the  skin  or  the  lower  part 
of  the  alimentary  canal.  The  deficiency  of  fluid  in  the  body  may 
arise, — and  Thirst  may  consequently  be  induced, — either  by  an  un- 
usually small  supply  of  fluid,  or  by  excessive  loss  of  the  fluids  of  the 
body,  as  by  perspiration,  diarrhoea,  &c.  But  it  may  also  be  occasioned 
by  the  impression  made  by  particular  kinds  of  food  or  drink  upon  the 
alimentary  canal ;  thus  salted  or  highly-spiced  meat,  fermented  liquors 
when  too  little  diluted,  and  other  similar  irritating  agents,  excite  thirst ; 
the  purpose  of  which  sensation  is  evidently  to  cause  the  ingestion  of 
fluid,  by  which  these  substances  may  be  diluted,  and  their  irritating 
action  prevented. 


ABSORPTION  AND   SANGUIFICATION.  277 


CHAPTER  V. 

ABSORPTION   AND   SANGUIFICATION. 
1.  Absorption  from  the  Digestive   Cavity. 


\ 

"^%89.  So  long  as  the  Alimentary  matter  is  contained  in  the  digestive 
'  cavity,  it  is  as  far  from  being  conducive  to  the  nutrition  of  the  system, 
as  if  it  were  in  contact  with   the   external  surface.     It  is  only  when 
;  absorbed  into  the  vessels,  and  carried  by  the  circulating  current  into 
I  the  remote  portions  of  the  body,  that  it  really  becomes  useful  in  main- 
■  taining  the  vigour  of  the  system,  by  replacing  that  which  has  decayed, 
i  and  by  affording  the  materials  for  the  various  organic  processes  which 
i  are  continually  going  on.     Among  the  Invertebrated  animals,  we  find 
the  reception  of  alimentary  matter  into  the  circulating  system  to  be 
entirely  accomplished  through  the  medium  of  the  veins^  which  are  dis- 
!  tributed  upon  the  walls  of  the  digestive  cavity.     We  not  unfrequently 
observe,  that  the  intestinal  tube  is  completely  enclosed  within  a  large 
I  venous  sinus,  so  that  its  whole  external  surface  is  bathed  with  blood ; 
and  into  this  sinus,  the  alimentary  materials  would  appear  to  transude, 
through  the  walls  of  the  intestinal  canal,  to  become  mingled  with  the 
blood,  and  to  be  conveyed  with  its  current  into  the  remote  portions  of 
the  body.     Among  the  Vertebrata,  we  find  an  additional  set  of  vessels, 
interposed  between  the  walls  of  the  intestine  and  the  sanguiferous  sys- 
tem, for  the  purpose,  as  it  would  seem,  of  taking  up  that  portion  of  the 
nutritive  matter  which  is  not  in  a  state  of  perfect  solution,  and  of  pre- 
paring it  for  being  introduced  into  the  current  of  the  blood.     These 
vessels  are  the  lacteals  or  absorbents.     They  are  very  copiously  distri- 
]  buted   upon  the  w^alls  of  the  small  intestine,   commencing  near   the 
I  entrance  of  the  biliary  and  pancreatic   ducts ;   the  walls  of  the  large 
intestine  are  less  abundantly  supplied  with  them,  and  they  do  not  show 
I  themselves  in  the  villi  which  are  found  on  some  parts  of  the  lining  mem- 
I  brane  of  the  stomach,  although  the  walls  of  that  viscus  are  supplied  with 
j  lymphatic  absorbents. 

i       490.  Nevertheless  it  is  quite  certain,  that  substances  may  pass  into 
!  the  current  of  the  circulation,  which  have  been  presented  from  passing 
'   further  than  the  stomach ;  thus,  if  a  solution  of  Epsom-salts  be  intro- 
'   duced  into  the  stomach  of  an  animal,  and  its  passage  into  the  intestine 
I   be  prevented  by  a  ligature  around   the  pylorus,   its  purgative  action 
i    will  be  exerted  nearly  as  soon,  as  if  the  communication  between  the 
I    stomach  and  intestines  had  been  left  quite  free ;  or  if  a  solution  of 
prussiate  of  potash   be   introduced   into   the   stomach    under   similar 
circumstances,  the  presence  of  that  salt  in  the  blood  may  be  speedily 
demonstrated  by  chemical  tests.     It  appears  from  the  experiments  of 
.    MM.  Tiedemann  and  Gmelin,  that  when  various  substances  were  min- 
gled with  the  food,  which,  by  their  colour,  odour,  or  chemical  properties 
might  be  easily  detected, — such  as  gamboge,  madder,  rhubarb,  camphor, 


2r&s  ABSORPTION   AND   SANGUIFICATION. 

musk,  assafoetida,  and  saline  compounds, — they  were  seldom  found  in 
the  chyle,  though  many  of  them  were  detected  in  the  blood  and  in  the 
urine.  The  colouring  matter  appeared  t;o  be  seldom  absorbed  at  all ; 
the  odorous  substances  were  generally  detected  in  the  venous  blood  and 
in  the  urine,  but  not  in  the  chyle ;  whilst,  of  the  saline  substances, 
many  were  found  in  the  blood  and  in  the  urine,  and  only  a  very  few  in 
the  chyle. 

491.  This  passage  of  substances  in  a  state  of  perfect  solution,  from 
the  stomach  into  the  blood-vessels,  is  probably  due"  to  the  operation  of 
that  peculiar  modification  of  Capillary  Attraction,  which  is  called  En- 
dosmose.  When .  two  fluids  differing  in  density  are  separated  by  a 
thin  animal  or  vegetable  membrane,  there  is  a  tendency  to  mutual 
admixture  through  the  pores  of  the  membrane;  but  the  less  dense 
fluid  will  transude  with  much  greater  facility  than  the  more  dense  ; 
and  consequently  there  will  be  a  considerable  increase  on  the  side  of 
the'  denser  fluid;  whilst  very  little  of  this,  in  comparison,  will  have 
passed  towards  the  less  dense.  When  one  of  the  fluids  is  contained  in 
a,  sac  or  cavity,  the  flow  of  the  other  towards  it  is  termed  Endosmose, 
or  flow-inwards ;  whilst  the  contrary  current  is  termed  Exosmose  or 
flow-outwards.  Thus  if  the  csecum  of  a  fowl,  filled  with  syrup  or 
gum-water,  be  tied  to  the  end  of  a  tube,  and  be  immersed  in  pure 
water,  the  latter  will  penetrate  the  caecum  by  Endosmose,  and  will  so 
increase  the  volume  of  its  contents,  as  to  cause  the  fluid  to  rise  to  a 
considerable  height  in  the  attached  tube.  On  the  other  hand,  a  small 
proportion  of  the  gum  or  syrup  will  find  its  way  into- the  surrounding 
fluid  by  Exosmose.  But  if  the  csecum  were  filled  with  water,  and 
were  immersed  in  a  solution  of  gum  or  sugar,  it  would  soon  be  nearly 
emptied,  the  Exosmose  being  much  stronger  than  the  Endosmose. 
It  is  in  this  manner  that  we  may  cause  the  flattened  corpuscles  of  the 
blood  to  be  distended  into  spheres,  by  treating  them  with  water;  or 
may  empty  them  almost  completely,  by  immersing  them  in  syrup 
(§215);  since  their  contents  are  more  dense  than  the  surrounding 
fluid  in  the ; first  case,  so  that  they  will  be  augmented  by  Endosmose; 
whilst  they  are  less  dense  in  the  second,  so  as  to  be  diminished  by 
Exosmose. 

492.  How  it  seems-  to  be  in  this  manner,  that  substances  contaiiied 
in  the  cavity  of  the  stomach,  and  perfectly  dissolved  by  its  fluids,  are 
received  into  the  blood-vessels ;  for  as  the  blood  is  the  fluid  of  greater 
density,  it  will  have  a  tendency  to  draw  towards  it,  by  Endosmose, 
the  saline  and  other  matters,  which  are  in  a  state  of  perfect  solution 
in  the  stomach.  The  Mucous  membrane,  which  forms  the  inner  wall 
of  that  organ,'  is  most  copiously  supplied  with  blood-vessels;  partly, 
indeed,  that  they  may  afford  the  materials  of  the  gastric  secretion ;  but 
partly,  also,  that  they  may  take  up  the  substances,  which  are  capable 
of  entering  the  circulating  current  by  this  direct  channel.  The  move- 
ment of  blood  through  the  vessels,  tends  to  accelerate  the  permeation 
of  liquids  through  their  walls,  in  a  very  remarkable  degree :  as  may 
be  shown  by  the  following  simple  experiment.  If  a  membranous  tube, 
such  as  a  piece  of  the  small  intestine  or  of  a  large  vein  of  an  animal, 
be  fixed  by  one  extremity  to  an  opening  at  the  bottom  of  a  vessel 


ABSORPTION   OF   SOLUBLE   MATTERS  INTO   THE   VEINS.  279 

filled  with  water,  and  have  a  stopcock  attached  at  the  other  extre- 
mity, and  be  then  immersed  in  water  acidulated  with  sulphuric  or 
hydrochloric  acid,  it  will  be  some  time  before  the  acid  will  penetrate  to 
the  interior  of  the  tube,  which  is  distended  with  water;  but  if  the 
stopcock  be  opened,  and  the  water  be  allowed  to  discharge  itself,  the 
presence  of  the  acid  will  be  immediately  discovered  (by  tincture  of 
litmus)  in  the  liquid  which  flows  out.  Thus  th^  continuance  of  the  Cir- 
culation is  obviously  one  of  the  most  important  of  the  conditions  of 
Absorption.  It  is  whilst  passing  through  the  system  of  capillaries, 
which  forms  a  minute  plexus  immediately  b|tieath  the  free  surface  of 
the  mucous  membrane,  that  the  blood  thus  receives  an  admixture  of  the 
soluble  matters  contained  within  the  digestive  cavity ;  and  hence  it  is 
that  these  substances  are  detectible  in  the  ;blood  of  the  gastric  and 
mesenteric  veins,  sooner  than  in  any  part  of  the  arterial  system.  They 
are  very  rapidly  difiiised,  however,  through  tHe  general  circulation ;  and 
may  even  show  themselves  in  the  excretions  within  so  short  a  period, 
that  it  is  obvious  that  thoy  must  have  been  absorbed  immediately  on 
their  introduction  into  the  stomach.  Thus  Mr.  Erichsen  found  that  he 
was  able  to  detect  the  presence  of  ferrocyanide  of  potassium  in  the 
urine,  within  one  minute  after  it  had  been  swallowed  in  solution.  This, 
however,  was  only  when  it  was  taken  after  a  long  fast ;  more  commonly 
the  absorption  is  less  rapid ;  and  if  the  substance  be  introduced  within  an 
hour  or  two  after  a  full  meal,  it  may  be  as  much  as  half  an  hour  before 
its  presence  in  the  urine  gives  evidence  of  its  having  been  received  into 
the  circulating  current.  Although  it  is  difficult  to  speak  with  certainty 
on  the  point,  yet  there  appears  a  strong  probability,  that^,  both  in  the 
stomach  and  intestinal  tube,  the  absorption  of  nutritive  matters  in  a 
state  of  perfect  solution  (such  as  gum,  sugiar,  pectine,  gelatine,  and 
soluble  albumen)  is  thus  accomplished  through  the  medium  of  the  blood- 
vessels ;  which  also  take  up  the  chief  supply  of' water  that  is  required  by 
the  system.  It  is  difficult  else  to  see  the  purpose  of  the  extraordinary 
vascularity  of  the  mucous  membrane,  and  in  particular  of  those  filaments 

Fig.  82.  ' 


Distribution  of  Capillaries  in  the  Villi  of  the  Intestine. 

or  narrow  folds,  termed  villi,  which  so  thickly  cover  its  surface.  Each 
of  these  villi  is  furnished  with  a  plexus  of  minute  blood-vessels,  of 
which  the  larger  branches  may  even  be  seen  with  the  naked  eye,  when 
they  are  distended  with  blood  or  with  a  coloured  injection.  By  these 
villi,  the  vascular  surface  of  the  mucous  membrane  is  enormously 
extended.  In  Man,  they  are  commonly  cylindrical  or  nearly  so,  and 
are  from  about  a  quarter  of  a  line,  to  a  line  and  a  half  in  length ;  but 


280  ABSORPTION  AND   SANGUIFICATION. 

in  many  of  the  lower  animals,  they  are  spread  out  into  broader  laminae 
at  the  base,  and  are  connected  together  so  as  to  form  ridges  or  folds. 

493.  The  nutritive  materials  taken  up  by  the  blood-vessels  of  the  ali- 
mentary canal,  are  not  conveyed  directly  into  the  general  circulation ; 
for  they  are  first  submitted  to  the  agency  of  the  Liver.  All  the  veins 
which  return  the  blood  from  the  gastro-intestinal  capillaries,  converge 
into  the  portal  trunk,  which  distributes  it  to  the  various  portions  of  that 
secreting  apparatus ;.  and  there  is  strong  reason  to  believe,  that  not 
merely  is  the  fluid  there  depurated  of  some  matters  whose  presence 
would  be  injurious,  but  that  the  Liver  exercises  a  powerful  assimilating 
action  upon  the  proper  nutritive  substances,  rendering  them  fitter  to 
become  components  of  the  Blood.  For  the  blood  of  the  portal  vein, 
when  examined  during  digestion,  is  found  to  contain  a  large  proportion 
of  albumen  and  comparatively  little  fibrine ;  whilst  in  that  which  has 
passed  through  the  liver,  the  amount  of  fibrine  has  undergone  a  large 
increase.  Again,  it  appears  that  fatty  matters  are  elaborated  in  the 
liver,  either  from  saccharine  substances,  or  from  albuminous  compounds ; 
for  even  when  no  fat  can  be  detected  in  the  blood  of  the  vena  portae, 
that  of  the  hepatic  vein  contains  it  in  considerable  amount.  So,  again, 
it  appears  that  the  liver  elaborates  from  some  other  constituents  of  the 
blood  a  saccharine  compound  (diabetic  sugar),  which  is  destined  for  im- 
mediate elimination  by  the  lungs,  and  which,  being  much  more  readily 
carried  ofi"  by  the  respiratory  process  than  either  grape-sugar  or  cane- 
sugar,  may  be  regarded  as  its  most  appropriate  pabulum.  Further,  if 
white  of  egg  mixed  with  water  be  injected  into  any  of  the  systemic  veins, 
distinct  evidence  of  the  presence  of  albumen  is  speedily  traceable  in  the 
urine ;  showing  that  this  substance  has  not  been  properly  assimilated. 
But  if  the  same  fluid  be  injected  into  the  portal  system,  no  trace  of  its 
presence  in  the  urine  is  found.  So,  again,  when  a  solution  of  sugar  is 
injected  into  the  general  venous  system,  this  substance  soon  shows  itself 
in  the  urinary  excretion ;  but  if  the  same  injection  be  made  into  the 
vena  portae,  so  that  the  sugar  is  obliged  to  pass  through  the  liver,  no 
such  elimination  takes  place,  it  being  then  assimilated  with  the  blood. 
The  liver,  however,  is  not  required  to  eff'ect  a  corresponding  change  in 
the  fatty  matters  taken  up  from  the  food ;  for  these  are  received  into 
the  blood  through  the  absorbents,  rather  than  through  the  sanguiferous 
vessels;  and  it  is  found  that  if  fatty  matters  be  injected  into  the  general 
circulation,  no  eff'ect  is  produced  on  the  urine.* 

494.  Every  one  of  the  intestinal  Villi,  however,  also  contains  the 
commencement  of  a  proper  lacteal  vessel ;  the  portion  of  the  absorbent 
system  specially  adapted  for  the  reception  of  alimentary  matters  from 
without,  being  thus  distinguished,  on  account  of  the  milky  aspect  of  the 
fluid  which  is  found  within  it.  The  following  figure  (83)  represents  the 
appearance  off"ered  by  the  incipient  lacteals,  in  a  villus  of  the  jejunum 
of  a  young  man,  who  had  been  hung  soon  after  taking  a  full  meal  of 
farinaceous  food.  The  trunk  that  issues  from  the  villus  is  formed  by 
the  confluence  of  several  smaller  branches,  whose  origin  it  is  difficult  to 
trace ;  but  it  is  probable  that  they  form  loops  by  anastomosis  with  each 

*  See  the  recent  Lectures  and  Memoirs  of  M.  CI.  Bernard,  in  "  L'Union  M^dicale," 
and  the  "Gazette  M^dicale,"  for  1850. 


One  of  the  Intestinal  Villi, 


ABSORPTION   OF   ALCOHOL,  ETC. — MESENTERIC   GLANDS.  281 

other,  so  that  there  is  no  proper  free  extremity  in  any  case.  It  is  quite 
certain  that  the  lacteals  never  open  by  free  orifices  upon  the  surface 
of  the  intestine,  as  was  formerly  imagined.  And  there  seems  good 
reason  to  believe,  that  either  by  the  cells  asserted  by  Prof.  Goodsir 
to  be  developed  within  the  free  extremities  of  the  villi,  or  by  the  epi- 
thelial cells  which  cover  their  extremities  (§  243),  a 
selection  is  made  of  those  substances  which  are  proper  Fig.  83. 

to  be  received  into  the  special  Absorbent  system. 

495.  It  is  particularly  important  to  keep  in  view 
the  difi'erence  between  the  two  modes,  by  which  ali- 
mentary substances  are  introduced  into  the  system, 
when  we  are  treating  those  disordered  states,  in 
which  the  digestive  process  is  imperfectly  performed, 
or  is  altogether  suspended.  There  can  be  little 
doubt  that  the  irnmediate  cause  of  death,  in  many 
diseases  of  exhaustion,  is  the  want  of  power  to  main- 
tain the  heat  of  the  body ;  the  stomach  not  being 
able  to  digest  food,  and  the  special  absorbent  power  with\hVcommenc7menrof 
of  the  lacteals  being  altogether  suspended,  so  that  *  ^*'''^*^' 

the  inanition  is  as  complete,  as  if  food  were  altogether  withheld. 
Now  under  such  circumstances,  it  becomes  a  matter  of  the  greatest  im- 
portance to  present  a  supply  of  combustible  matter,  in  such  a  form  that 
it  may  be  introduced  into  the  circulating  system  by  simple  Endosmose ; 
and  the  value  which  experience  has  assigned  to  broths  g-nd  to  thin  fari- 
naceous solutions,  and  still  more,  to  diluted  alcoholic  drinks,  frequently 
repeated,  under  such  circumstances,  seems  to  depend  in  great  part  upon 
the  facility  with  which  they  may  be  thus  absorbed.  The  good  effects 
of  alcohol,  cautiously  administered,  are  no  doubt  owing  in  part  to  its 
specific  influence  upon  the  nervous  system ;  but  that  they  are  also  due 
to  its  heat-producing  power,  appears  from  the  results  of  the  administra- 
tion of  frequently-repeated  doses,  in  states  of  utter  exhaustion, — the 
temperature  of  the  body  being  kept  up  so  long  as  they  are  continued, 
and  falling  when  they  are  intermitted  (§  118).  As  the  alcohol  is  thus 
burned  off  nearly  as  fast  as  it  is  introduced,  it  never  accumulates  in 
sufficient  quantity,  to  produce  its  usual  violently-stimulating  effects  upon 
the  nervous  system. 

2.  Passage  of  the  Chyle  along  the  Lacteals,  and  its  admixture  with  the  Lymph 
collected  from  the  general  Systeiji. 

496.  The  Lacteal  vessels,  which  commence  on  the  surface  of  the  in- 
testines, run  together  on  their  walls,  and  form  larger  trunks,  which 
converge  and  unite  with  each  other  in  the  mesentery ;  and  the  main 
trunks  thus  formed  then  enter  certain  bodies,  which  are  commonly 
known  as  the  "mesenteric  glands."  Their  structure,  however,  does  not 
seem  to  correspond  with  that  of  the  proper  glands ;  as  they  are  simply 
composed  of  lacteal  trunks,  convoluted  into  knots,  and  dilated  into 
larger  cavities,  amongst  which  blood-vessels  are  minutely  distributed. 
These  blood-vessels  have  no  direct  communication  with  the  interior  of 
the  lacteals;  but  are  separated  from  them  by. the  membranous  walls  of 


282 


ABSOKPTION  AND   SANGUIFICATtON. 


both  sets  of  tubes.  The  epithelium,  which  lines  the  absorbent  vessel, 
undergoes  a  marked  change  where  the  vessel  enters  the  gland,  and  be- 
comes more  .like  that  of  the  proper  glandular  follicles  in  its  character. 
Instead  of  being  flat  and  scale-like,  and  forming  a  single  layer  in' close 
apposition  with  the  basement-membrane,  as  it  does  in  the  lacteal  tubes 
before  they  enter  the  gland  and  after  they  have  emerged  from  it,  we 
find  it  composed,  within  the  gland,  of  numerous  layers  of  spherical  nu- 
cleated cells  (Figs.  84  and  85) ;  of  which  the  superficial  ones  are  easily 
detached,  and  appear  to  be  identical  with  the  cells  that  are  found  float- 
ing in  the  chyle.  The  purpose  of  the  cells  will  be  presently  inquired 
into. 


Fig.  84. 


Fig.  85. 


Diagram  of  an  Absorbent  Gland,  showing  the 
intra-glandular  network,  and  the  transition  from 
the  scale-like  epithelia  of  the  extra  glandular  ab- 
sorbents, to  the  nucleated  cells  of  the  intra-glan- 
dular. 


Portion  of  intra-glandular  Absorbent,  showing 
along  the  lower  edge  the  thickness  of  the  germi- 
nal membrane,  and  upon  it,  the  thick  layer  of 
glandular  epithelial  cells. 


497.  After  emerging  from  the  mesenteric  glands,  the  lacteal  trunks 
converge,  with  occasional  union,  until  they  discharge  their  contents  into 
the  receptaculum  cTiyli,  which  is  situated  at  the  front  of  the  body  of  the 
second  lumbar  vertebra.  Into  the  same  cavity  are  poured  the  contents 
of  a  part  of  the  other  division  of  the  Absorbent  system ;  which  is  dis- 
tributed through  the  body  in  general,  and  which,  from  the  transparency 
of  the  fluid  or  lymph  it  contains,  is  termed  the  lymphatic  system.  From 
the  receptaculum  chyli,  arises  the  thoracic  duct ;  which  pass  upwards  in 
front  of  the  spine,  receiving  other  lymphatic  trunks  in  its  course,  to 
terminate  at  the  junction  of  the  left  subclavian  and  jugular  veins ;  where 
it  delivers  its  contents  into  the  sanguiferous  system  (Fig.  86).  A  smaller 
duct  receives  some  of  the  lymphatics  of  the  right  side,  and  there  termi- 
nates at  a  corresponding  part  of  the  venous  system ;  but  it  does  not 
receive  any  of  the  contents  of  the  lacteals. 

498.  The  Lymphatic  system  is  evidently  allied  very  closely  to  the 
lacteal,  in  its  general  purposes  ;  and  makes  its  first  appearance  in  the 
same  class  of  animals,  namely,  in  fishes.  The  vessels  of  which  it  is 
composed  are  distributed  through  most  of  the  softer  tissues  of  the  body, 
and  are  particularly  abundant  in  the  skin.  They  have  never  been  found 
to  commence  by  closed  or  open  extremities ;  but  seem  to  form  a  net- 
work, from  which  the  trunks  arise.  In  their  course  they  pass  through 
glandulse,  disposed  in  different  parts  of  the  body,  which  exactly  re- 
semble in  structure  those  which  are  found  upon  the  lacteals  in  the 
mesentery.  And  they  at  last  terminate,  as  already  shown,  in  the  same 
general  receptacle  with  the  lacteals.  Hence  it  cannot  be  reasonably 
doubted  that  the  fluid  which  they  absorb  from  the  various  tissues  of  the 
body,  is  destined  to  become  again  subservient  to  nutrition  ;  being  poured 
back  into  the  current  of  the  blodd,  along  with  the  new  materials,  which 


LACTEAL   AND    LYMPHATIC    SYSTEMS. 


283 


Fig.  86. 


re  now  for  the  first  time  being  introduced  into  it.  That  the  special 
Absorbent  apparatus  of  Yertebrated  animals  has  for  part  of  its  functions 
to  effect  a  change  in  the  materials 
absorbed,  and  thus  to  aid  in  fitting 
them  for  introduction  into  the  blood, 
seems  apparent  from  the  facts  of 
Comparative  Anatomy ;  which  show 
that,  the  more  distinct  the  blood  is 
from  the  chyle  and  lymph,  the  more 
marked  is  the  provision  for  delaying 
the  latter  in  the  absorbent  system, 
and  for  subjecting  it  to  preliminary 
change. 

499.  The  course  of  the  Absorbent 
vessels  in  Fishes  is  short  and  simple ; 
they  are  not  furnished  with  glands  ; 
and  they  pour  their  contents  into 
the  blood-vessels  at  several  different 
parts  of  the  body.  In  this  class  the 
blood  contains  fewer  red  corpuscles, 
and  its  coagulating  power  is  feebler, 
than  in  any  other  Vertebrata.  And 
in  the  lowest  tribes,  in  which  the 
Vertebrated  character  is  almost  en- 
tirely wanting,  and  in  which  the 
blood  is  almost  pale,  no  special  ab- 
sorbent system  has  yet  been  dis- 
covered.— In  Reptiles^  the  length  of 
the  Absorbent  vessels  is  remarkably 
increased  by  their  doublings  and 
convolutions  ;  so  that  the  system  ap- 
pears to  be  more  highly  developed, 
than  in  either  of  the  warm-blooded 
classes.  But  this  superiority  is  not 
real ;  for  there  is  yet  no  trace  of  the 
glands,  which  concentrate,  as  it  were, 
the  assimilation  power,  of  a  long  se- 
ries of  vessels.  Moreover,  we  often 
find  the  lymphatics  of  this  class  fur- 
nished with  pulsating  dilatations,  or 
lymphatic  hearts;  which  have  for 
their  office  to  propel  the  lymph  into 
the  venous  system.  In  the  Frog 
there  are  two  pairs  of  these ;  one  situ- 
ated just  beneath  the  skin  (through 
which  its  pulsations  are  readily  seen 
in  the  living  animal),  immediately 

behind  the  hip-joint ;  the  other  pair  being  more  deeply  seated  at  the 
upper  part  of  the  chest.  The  former  receive  the  lymph  of  the  posterior 
part  of  the  body,  and  pour  it  into  the  veins  proceeding  from  the  same 


The  course  and  termination  of  the  Thoracic 
Duct.  1.  The  arch  of  the  aorta.  2.  The  thoracic 
aorta.  3.  The  abdominal  aorta;  showing  its 
principal  branches  divided  near  their  origin.  4. 
The  arteria  innominata,  dividing  into  the  right 
carotid  and  right  subclavian  arteries.  5.  The 
left  carotid.  6.  The  left  subclavian.  7.  The  su- 
perior cava,  formed  by  the  union  of,  8,  the  two 
venaj  innominatje;  and  these  by  the  junction,  9, 
of  the  internal  jugular  and  subflavian  vein  at 
each  side.  10.  The  greater  vena  azygos.  11.  The 
termination  or  the  lesser  in  the  greater  vena 
azygos.  12.  The  receptaculum  chyli;  several 
lymphatic  trunks  are  seen  opening  into  it.  13. 
The  thoracic  duct,  dividing  opposite  the  middle  of 
the  dorsal  vertebrae  into  two  branches,  which  soon 
reunite  ;  the  course  of  the  duct  behind  the  arch  of 
the  aorta  and  left  subclavian  artery  is  shown  by  a 
dotted  line.  14.  The  duct  making  its  turn  at  the 
root  of  the  neck,  and  receiving  several  lymphatic 
trunks  previously  to  terminating  in  the  posterior 
aspect  of  the  junction  of  the  internal  jugular  and 
subclavian  vein.  15.  The  termination  of  the  trunk 
of  the  ductus  lymphaticus  dexter. 


284  '  ABSORPTION  AND   SANGUIFICATION. 

part ;  the  latter  collect  that  which  is  transmitted  from  the  anterior  part 
of  the  body  and  head,  and  empty  their  contents  into  the  jugular  vein. 
Their  pulsations  are  totally  independent  of  the  action  of  the  heart,  and 
of  the  respiratory  movements ;  since  they  continue  after  the  removal  of 
the  former,  and  for  an  hour  or  two  subsequently  to  the  death  and  com- 
plete dismemberment  of  the  animal.  They  usually  take  place  at  the 
rate  of  about  sixty  in  the  minute ;  but  they  are  by  no  means  regular, 
and  are  not  synchronous  on  the  two  sides. 

500.  In  Birds,  we  find  the  Absorbent  system  existing  in  a  more  per- 
fect form ;  its  diffused  plexuses  and  convolutions  being  replaced  by  glands ; 
in  which  the  contained  fluid  is  brought  into  closer  proximity  with  the 
blood,  and  in  which  it  is  subjected  to  the  influence  of  assimilating  cells. 
These,  however,  are  not  very  numerous ;  being  principally  found  on  the 
lymphatics  of  the  upper  extremities.  The  absorbents,  in  this  class, 
terminate  principally  by  two  thoracic  ducts,  one  on  each  side,  which 
enter  the  jugular  veins  by  several  orifices.  There  are,  however,  two 
other  entrances,  as  in  Reptiles,  into  the  veins  of  the  lower  extremity ; 
and  these  are  connected  with  two  large  dilatations  of  the  lymphatics, 
which  are  evid<jntly  analogous  to  the  lymphatic  hearts  of  Reptiles,  but 
which  have  little  or  no  power  of  spontaneous  contraction. — In  Mam- 
malia, the  Absorbent  system  presents  itself  in  its  most  developed  and 
concentrated  state.  The  vessels  possess  firmer  walls,  and  are  more 
copiously  provided  with  valves,  than  in  the  classes  beneath ;  and  the 
glands  are  much  more  numerous,  particularly  upon  the  vessels  that 
receive  or  imbibe  substances  from  without, — as  those  of  the  digestive 
cavity,  the  skin,  and  the  lungs.  The  terminations  of  the  absorbents  in 
the  veins  are  usually  restricted,  as  in  Man,  to  the  single  point  of  en- 
trance of  the  thoracic  duct  on  either  side ;  but  they  are  sometimes  more 
numerous ;  and  certain  variations  in  the  arrangement  of  the  thoracic 
ducts,  which  occasionally  present  themselves  as  irregularities  in  Man, 
are  the  ordinary  conditions  of  these  parts  in  some  of  the  lower  Mam- 
malia. 

501.  With  regard  to  the  source  of  the  matters  absorbed  by  the 
Lymphatics,  it  is  difiicult  to  speak  with  certainty.  We  shall  presently 
see  that  their  contents  bear  a  close  resemblance  to  the  fluid  element  of 
the  blood,  or  "  liquor  sanguinis,"  in  a  state  of  dilution ;  and  it  is  very 
probable  that  they  partly  consist  of  the  residual  fluid,  which,  having 
escaped  from  the  blood-vessels  into  the  tissues,  has  furnished  the  latter 
with  the  materials  of  their  nutrition,  and  is  now  to  be  returned  to  the 
former.  But  they  may  include,  also,  those  particles  of  the  solid  frame- 
work, which  have  lost  their  vital  powers,  and  which  are,  therefore,  not 
fit  to  be  retained  as  components  of  the  living  system,  but  which  have  not 
undergone  a  degree  of  decay  which  prevents  them  from  serving,  like 
matter  derived  from  the  dead  bodies  of  other  animals,  as  a  material  for  re- 
construction, when  it  has  been  again  subjected  to  the  organizing  process. 

502.  It  was  formerly  supposed  (and  the  doctrine  was  particularly  in- 
culcated by  the  celebrated  John  Hunter)  that  the  ofiice  of  the  Lymphatic 
system  is  to  take  up  and  remove  all  the  efi'ete  matter,  that  is  to  be  cast 
out  of  the  body,  being  no  longer  fit  for  its  nutrition.  But  for  such  a 
supposition  there  is  no  adequate  foundation.     It  seems  absurd  to  ima- 


ABSORPTION   BY  THE   LYMPHATICS.  285 

gine,  that  this  effete  matter  would  be  mingled  with  the  newly-ingested 
aliment,  and  would  be  poured  back  with  it  into  the  general  current  of 
the  circulation,  instead  of  being  at  once  carried  out  of  the  system.  And 
the  idea  is  directly  negatived,  as  we  shall  presently  see,  by  the  actual 
composition  of  the  lymph  drawn  from  these  vessels  ;  the  solid  matter  of 
which  consists,  in  great  part  at  least,  of  substances  of  a  nutritive  cha- 
racter. It  is  true  that  other  substances  are  occasionally  found  in  the 
lymphatics  ;  thus,  when  the  gall-bladder  and  bile-ducts  are  over-dis- 
tended with  bile,  in  consequence  of  some  obstruction  to  its  exit,  the 
lymphatics  of  the  liver  are  found  to  contain  a  biliary  fluid.  In  like 
manner,  the  lymphatics  in  the  neighbourhood  of  a  large  abscess  have 
been  found  to  contain  pus.  When  the  limb  of  an  animal,  round  the 
upper  part  of  which  a  bandage  is  tied,  is  kept  for  some  hours  in  tepid 
milk,  the  lymphatics  of  the  skin  are  found  distended  with  that  fluid. 
And  when  saline  solutions  are  applied  to  the  skin,  they  are  usually 
detected  more  readily  in  the  lymphatics,  than  in  the  veins.  But  these 
facts  only  prove,  that  the  lymphatics  very  readily  imbibe  soluble  sub- 
stances with  which  they  are  in  proximity ;  and  this  imbibition  seems  to 
take  place  on  the  same  physical  principles,  as  the  imbibition  of  soluble 
substances  by  the  veins  of  the  intestinal  canal. 

503.  The  more  ready  absorption  of  such  substances  by  the  lympha- 
tics, than  by  the  veins,  of  the  cutaneous  surfaces, — contrary  to  what 
obtains  in  the  alimentary  canal, — is  easily  accounted  for,  by  the  very 
abundant  distribution  of  the  lymphatics  in  the  skin,  and  the  ready 
access  which  fluids  can  obtain  to  their  walls.  In  other  tissues  it  is 
different :  thus  it  appears  that  saline  matters  injected  into  the  lungs 
are  detected  much  sooner  in  the  serum  of  the  blood,  than  they  are  in 
the  lymph ;  and  make  their  appearance  earlier  in  the  left  cavities  of 
the  heart,  to  which  they  would  be  conveyed  by  the  pulmonary  vein, 
than  in  the  right,  which  they  would  reach  through  the  thoracic  duct 
and  descending  cava.  This  is  obviously  due  to  the  minute  distribution 
of  the  blood-vessels  upon  the  walls  of  the  air-cells  ;  which  makes  them 
far  more  ready  channels  for  the  imbibition  of  fluid,  thau  the  lym- 
phatics could  be. — In  regard  to  the  occasional  absorption  of  pus  from 
the  cavity  of  an  abscess  or  of  an  open  ulcer,  by  the  lymphatics,  it  is  to 
be  remarked  that  the  absorbent  vessels  must  themselves  probably  be 
laid  open  by  ulceration  ;  since  in  no  other  way  can  we  understand  the 
entrance  of  the  globules,  so  large  as  those  of  pus,  into  their  interior. 

504.  In  regard  to  the  cause  of  the  movement  ^of  the  chyle  and  lymph 
along  the  absorbent  vessels,  from  their  commencement  to  their  termina- 
tion in  the  central  receptacle,  no  very  definite  account  can  be  given. 
The  middle  coat  of  these  vessels  has  a  fibrous  texture ;  and  the  fibres 
bear  some  resemblance  to  that  of  the  non-striated  muscle.  In  the 
thoracic  duct,  this  fibrous  structure  is  more  evident;  and. distinct  con- 
tractions have  been  excited  in  it,  by  irritating  the  sympathetic  trunks 
from  which  it  receives  its  nerves,  and  the  roots  of  the  spinal  nerves  with 
which  those  trunks  are  connected.  Hence  it  seems  probable,  that  there 
is  a  sort  of  peristaltic  contraction  of  the  Wlalls  of  the  absorbents, 
analogous  to  that  which  takes  place  in  the  intestinal  tube,  serving  to 
drive  their  contents  slowly  onwards  ;  their  reflux  being  prevented  by 


286  ABSORPTION  AND   SANGUIFICATION. 

the  valves,  with  which  they  are  copiously  furnished.  Moreover,  it  is 
probable  that  the  general  movements  of  the  body  may  concur  with  the 
contractile  power  of  the  absorbent  vessels  themselves,  to  urge  their  con- 
tents onwards;  for  .almost  every  change  in  position  must  occasion 
increased  pressure  on  some  portion  of  them,  which  will  propel  the  fluid 
contents  in  the  sole  direction  permitted  by  the  valves,  and  thus  give 
them  an  additional  impulse  towards  the  trunks,  in  which  they  are  col- 
lected for  delivery  into  the  blood-vessels. 

3.  Of  the  Spleen  J  and  other  Glandular  Appendages  to  the  Lymphatic  System. 

505.  The  structure  and  functions  of  the  Spleen,  and  of  certain  other 
organs  allied  to  it  in  character,  have  been  among  the  most  obscure 
subjects  in  Anatomy  and  Physiology ;  and  they  are  far  from  having 
been  yet  fully  elucidated.  There  seems  sufiicient  evidence,  however, 
for  regarding  them  in  th'e  light  of  appendages  to  the  Absorbent 
system,  and  as  concerned,  like  it,  in  the  process  of  Sanguification,  or 
the  preparation  of  Blood.  Hence  this  appears  to  be  the  most  appro- 
priate place  for  such  a  brief  notice  of  them  as  the  present  state  of  our 
knowledge  admits. 

506.  The  Spleen  is  certainly  to  be  regarded  as  an  organ  of  compound 
structure,  having  at  least  two  sets  of  functions  to  fulfil.  It  is  essen- 
tially composed  of  a  fibrous  membrane,  which  constitutes  its  exterior 
envelope,  and  which  sends  prolongations  in  all  directions  across  its  in- 
terior, so  as  to  divide  it  into  a  number  of  minute  cavities  of  irregular 
form,  freely  communicating  with  each  other.  In  many  animals,  this 
fibrous  envelope,  and  the  prolongations  or  traheculce  which  it  sends 
through  the  substance  of  the  organ,  are  distinctly  muscular ;  containing 
a  large  proportion  of  the  peculiar  fusiform  contractile  cells  formerly 
described  (§  337).  These,  however,  do  not  present  themselves  in  the 
.Human  spleen ;  and  its  trabeculae  do  not  appear  to  have  any  contractile 
property.  The  areolae  formed  by  the  trabecular  tissue,  commonly 
known  as  the  splenic  follicles,  are  difi*erently  occupied  in  different  ani- 
mals. In'  the  Ruminants  they  are  lined  by  a  continuation  of  the 
splenic  vein,  which  dilates  into  a  cavernous  structure,  capable  of  re- 
ceiving a  very  large  quantity  of  blood.  In  Man,  however,  they  have 
no  communication  with  the  splenic  vein,  and  are  chiefly  occupied  by 
the  Malpighian  corpuscles  and  the  parenchymatous  tissue,  which,  in  the 
Ruminants,  are  limited  to  the  partitions  between  the  venous  cells.  The 
Malpighian  corpuscles  of  the  spleen  are  whitish  spherical  bodies,  which 
are  always  connected  with  the  smaller  arteries,  like  currants  with  their 
stalks ;  being  sometimes  in  immediate  contact  with  them,  but  more 
commonly  being  connected  by  a  peduncle.  Their  size,  when  fully 
formed,  varies  from  l-3d  to  l-6th  of  a  line.  Each  of  them  contains, 
as  its  constant  and  essential  elements,  nucleated  cells  from  l-4000th  to 
l-2500th  of  an  inch  in  diameter,  pale  and  faintly  granular,  together 
with  free  nuclei,  as  well  as  larger  cells  of  l-2000th  of  an  inch  in 
diameter,  which  sometimes  contain  what  appear  to  be  red  blood-cor- 
puscles.    These  are  enclosed  in  a  capsule,  which  has  no  orifice,  and 


STRUCTURE   AND   FUNCTIONS   OF   THE   SPLEEN.  287 

which  appears  to  be  comparable  to  the  elementary  vesicles  of  other 
glands,  before  they  have  acquired  an  outlet  by  the  rupture  of  their 
walls  (§  718).  Whatever  may  be  the  function  of  these  bodies,  it  is  pro- 
bable that  it  must  be  completed  by  the  rupture  of  the  capsules  and  the 
discharge  of  their  contents  ;  and  that  new  corpuscles  are  continually  in 
course  of  development. — The  true  splenic  parenchyma  consists  in  great 
part  of  cells  which  correspond  in  appearance  with  those  of  the  Mal- 
pighian  corpuscles ;  but  in  addition  to  these,  there  are  cells  which  bear 
a  strong  likeness  to  the  colourless  'granule-cells'  of  the  blood  (§  217), 
and  others  which  resemble  young  red-corpuscles.  These  elements,  also, 
present  indications  of  being  in  a  state  of  continual  development  and 
degeneration;  and  form  small  irregular  groups  of  various  sizes,  which 
are  clustered  especially  on  the  sheaths  of  the  vessels,  the  trabecular 
partitions,  and  the  exterior  of  the  Malpighian  capsules. — A  considerable 
part  of  the  contents  of  the  splenic  areolae  has  been  found  by  Prof. 
Kolliker  to  consist  of  blood-corpuscles  in  various  stages  of  degenerative 
metamorphosis.  These  are  aggregated  in  small  masses,  each  of  which 
acquires  an  investing  membrane,  that  may  contain  from  one  to  twenty 
corpuscles ;  and  the  blood-cells  gradually  diminish  in  size,  and  undergo 
a  transition  into  pigment-granules;  so  that  the  containing  cells  are 
converted  into  pigmentary  granule-cells,  which  at  last,  by  a  gradual 
loss  of  colour  of  the  granules,  become  quite  pale.  Such  cells  are  found 
in  the  blood  drawn  from  the  splenic  vein,  the  vena  portse,  and  the  in- 
ferior cava;  and  occasionally  in  that  of  other  veins.  These  curious 
collections  of  degenerating  blood-corpuscles,  however,  are  not  peculiar 
to  the  spleen,  for  they  have  been  found  by  Prof.  Kolliker  in  other  parts, 
such  as  the  substance  of  the  muscles.  ■ 

507.  In  regard  to  the  functions  of  the  Spleen,  great  uncertainty  still 
exists.  It  appears  from  the  foregoing  account  of  its  structure,  that  it 
may  be  regarded  as  an  organ  of  duplex  character,  and  probably  of 
double  function.  In  the  Ruminants,  the  cavernous  dilatations  of  the 
veins  enable  it  to  hold,  upon  occasion,  a  large  quantity  of  blood ;  and 
their  walls  are  so  elastic,  that  their  cavities  may  be  greatly  distended 
with  a  very  moderate  force ;  the  Spleen  of  the  sheep,  which  weighs 
about  4  oz.,  being  easily  made  to  contain  about  30  oz.  of  water.  This 
peculiar  distensibility  evidently  points  to  the  Spleen,  as  a  kind  of 
reservoir,  connected  with  the  Portal  circulation,  for  the  purpose  of 
relieving  the  portal  vessels  from  undue  pressure  or  distension,  under  a 
great  variety  of  circumstances.  The  portal  system  is  well  known  to 
be  destitute  of  valves,  so  that  the  splenic  vein  conimunicates  freely  with 
the  whole  of  it ;  and  thus,  if  any  obstruction  exists  to  the  flow  of  blood 
through  the  liver,  or  any  peculiar  pressure  elsewhere  prevents  the 
mesenteric  veins  from  dilating  to  their  full  extent,  the  general  circula- 
tion is  not  disturbed,  the  Spleen  affording  a  kind  of  safety-valve.  That 
any  cause  of  congestion  of  the  Portal  system  peculiarly  affects  the 
Spleen,  has  been  proved  by  experiment ;  for,  after  the  portal  vein  has 
been  tied,  the  spleen  of  an  animal  that  previously  weighed  only  2  oz., 
has  been  found  to  increase  to  20  oz.— Again,  the  Spleen  appears  to 
serve  as  a  reservoir,  into  which  superfluous  blood  may  be  carried,  during 
the  digestive  process.     When  the  alimentary  canal  is  distended  with 


288  ABSORPTION  AND  SANGUIFICATION. 

food,  and  a  great  afflux  of  arterial  blood  takes  place  to  the  mucous 
membrane,  the  veins  of  the  portal  system  will  be  liable  to  increased 
pressure  from  without,  whilst  their  contents  will  be  augmented  by  the 
quantity  of  fluid  newly  absorbed  from  the  alimentary  canal.  In  this, 
as  in  the  preceding  cases,  the  distensibility  of  the  spleen  makes  it  a 
kind  of  safety-valve,  by  which  undue  distension  of  the  portal  system  is 
relieved.  It  has  been  ascertained  that  its  maximum  volume  is  attained 
about  five  hours  after  a  meal,  when  the  process  of  chymification  is  at  an 
end,  and  that  of  absorption  is  taking  place  with  activity ;  and  the  in- 
crease is  proportional  rather  to  the  amount  of  the  fluids  ingested,  than 
to  that  of  the  solids. — Although  the  Human  Spleen  has  no  true  cavern- 
ous structure,  yet  its  veins  are  obviously  very  distensible,  so  that  a  great 
accumulation  of  blood  may  take  place  in  it.  Thus,  in  Asphyxia,  when 
the  circulation  of  blood  is  checked  in  the  Lungs,  and  when  the  stagna- 
tion extends  itself  backwards  to  the  right  side  of  the  heart,  the  vena 
cava,  and  thence  to  the  portal  system,  the  Spleen  is  often  found  after 
death  to  be  enormously  distended  with  blood.  And  in  the  cold  stage 
of  intermittent  fever,  in  which  a  great  quantity  of  blood  is  driven  from 
the  surface  towards  the  internal  organs,  the  Spleen  receives  a  large 
portion  of  it,  so  that  its  increased  size  becomes  quite  perceptible;  and 
in  cases  of  confirmed  Ague,  the  Spleen  becomes  permanently  enlarged, 
forming  what  is  popularly  known  as  the  "ague-cake." 

508.  But  besides  this  safety-valve  function,  there  can  be  little  ques- 
tion that  the  Spleen  performs  some  other,  which  is  related  more  closely 
to  the  nutritive  operations,  and  which  in  some  degree  correspond  with 
that  performed  by  the  Absorbent  glandulse.  The  multitude  of  glandu- 
lar cells  in  immediate  relation  with  blood-vessels,  and  the  appearances 
of  rapid  development  and  degeneration  which  these  present,  taken  in 
connexion  with  the  fact  that  there  is  no  other  outlet  for  the  products  of 
their  action  than  that  which  is  aff'orded  by  the  veins,  clearly  indicate 
that  whatever  this  product  may  be,  it  is  destined  to  form  part  of  the 
blood;  and  that  the  Spleen  is,  therefore,  an  organ  of  sanguification. 
This  view  is  confirmed  by  the  remarkable  fact,  ascertained  by  recent 
experiments,  that  after  the  spleen  has  been  extirpated,  the  lymphatic 
glands  of  the  neighbourhood  increase  in  size,  and  cluster  together  as 
they  enlarge,  so  as  to  form  an  organ  which  at  least  equals  the  original 
spleen  in  volume.  This  circumstance  explains  the  reason  for  the  almost 
invariable  negative  result  of  the  extirpation  of  the  spleen ;  for  although 
the  operation  has  been  frequently  practised,  "with  the  view  of  deter- 
mining the  functions  of  the  organ  by  the  symptoms  presented  by  the 
animals  after  its  removal,  no  decided  change  in  the  ordinary  course  of 
their  vital  phenomena  has  ever  been  observed,  and  the  health,  if  at  all 
disturbed  for  a  time,  is  afterwards  completely  regained.  Now  if  the 
principal  function  of  the  Spleen  be  the  same  with  that  of  the  lymphatic 
glands  in  general,  it  is  easy  to  understand  how  its  loss  may  be  at  once 
compensated  by  an  increased  action  on  their  part,  and  how  it  may  be 
permanently  replaced  by  an  increased  development  of  certain  of  those 
bodies. — It  is  worthy  of  remark,  that  a  Spleen  is  found  in  all  Yerte- 
brated  animals  which  have  a  distinct  Absorbent  system ;  but  that  no 
organ  exactly  corresponding  with  it  exists  in  the  Invertebrata,  which 


STRUCTURE  AND   FUNCTIONS   OF   THE   SPLEEN.  289 

We  destitute  of  that  system, — although  the  distensible  cellated  cavities, 
apparently  destined  to  perform  its  safety-valve  function,  exist  in  some 
of  the  higher  among  them.  This  is  an  additional  reason  for  regarding 
its  parenchymatous  portion  as  essentially  a  part  of  the  assimilating  ap- 
paratus of  the  Absorbent  system. 

509.  It  would  further  seem  as  if  the  Spleen  were  specially  concerned 
in  the  development  of  the  red  corpuscles  of  the  blood ;  since  its  paren- 
chyma contains  cells  which  resemble  these  in  various  stages  of  develop- 
ment. But  this  organ  also  appears  to  promote  the  disintegration  of 
those  red  corpuscles  which  have  become  effete ;  and  this  so  powerfully, 
that  the  blood  of  the  splenic  vein  contains  a  far  less  proportion  of  red 
corpuscles,  and  a  far  greater  proportion  of  albumen,  than  that  of  any 
other  vessels  in  the  body.  It  is  supposed  by  Prof.  Kblliker,  that  the 
dissolved  blood-corpuscles  are  subservient  'to  the  formation  of  bile ;  the 
colouring  matter  of  which  is  nearly  allied  to  that  of  the  blood. 

510.  The  Supra-Renal  Capsules  seem  to  correspond  with  the  Spleen 
in  their  essential  structure,  whilst  in  the  arrangement  of  their  compo- 
nent parts,  they  bear  more  resemblance  to  the  Kidney.  Their  exterior 
or  cortical  portion,  in  Man  and  the  Mammalia  generally,  is  formed  of 
straight  arteries,  which  divide  into  a  minute  capillary  network;  and 
from  this  arise  venous  branches,  which  form  a  minute  plexus  through 
the  internal  or  medullary  substance,  pouring  its  contents  into  a  large 
central  cavity,  which  is  the  dilated  commencement  of  the  supra-renal 
vein.  In  the  lower  Vertebrata,  however,  there  is  no  distinction  of  cor- 
tical and  medullary  substance ;  the  distribution  of  vessels  being  nearly 
the  same  throughout.  As  in  the  Spleen,  we  find  in  the  interspaces  of 
the  vascular  plexus  a  parenchymatous  structure ;  partly  composed  of 
free  cells  and  nuclei  in  various  stages  of  development ;  and  partly  con- 
sisting of  closed  granular  vesicles,  within  which  similar  cells  and  nuclei 
are  included.  There  is  ground  for  asserting  that  these  vesicles  are 
themselves  at  first  in  the  condition  of  simple  cells,  and  that  the  cells 
which  they  include  are  a  secondary  product.  In  Man  and  the  Mam- 
malia, these  vessels  are  confined  to  the  cortical  substance,  and  have  the 
form  of  elongated  tubes,  lying  between  its  parallel  blood-vessels.  Thus, 
then,  the  supra-renal  capsules  possess  the  essential  structure  of  a  gland, 
in  every  respect  save  the  want  of  an  excretory  duct ;  and  whatever  may 
be  the  product  of  their  cell  action,  this  must  be  received  back  into  the 
blood  again.  The  fluid  contents  of  these  bodies;  are  rich  in  proteine 
compounds  and  in  fat ;  and  it  can  be  scarcely  doubted  that  these  mate- 
rials here  undergo  an  elaboration,  which  renders  them  better  fitted  for 
the  nutrition  of  the  system.  It  does  not  seem  unlikely  that  these  bodies, 
like  the  Spleen,  have  a  double  function  ;  and  that,  besides  plarticipating 
in  the  general  actions  of  the  Absorbent  glandulse,  they  may  serve  as  a 
diverticulum  for  the  Renal  circulation,  when  from  any  cause  the  se- 
creting function  of  the  Kidneys  is  retarded  or  checked,  and  the  move- 
ment of  blood  through  them  is  stagnated. — The  Supra-Renal  capsules 
of  Man  attain  a  very  large  size  early  in  foetal  life,  surpassing  the  true 
Kidneys  in  dimension  up  to  the  tenth  or  twelfth  week ;  but  they  after- 
wards diminish  relatively  to  the  latter,  and  are  evidently  subordinate 
organs  during  the  whole  remainder  of  life.     In  most  of  the  lower  ani- 

19 


290  ABSORPTION   AND   SANGUIFICATION. 

mals,  however,, these  bodies  retain  through  life  tho^  same  relative  deve- 
lopment. 

511.  The  Thymus  Gland  is  another  body,  which  seems  referrible  to 
the  same  group;  having  all  the  essential  characters  of  a  true  gland 
(§714),  save  an  excretory  duct;  and  its  function  being  evidently  con- 
nected, during  the  early  period  of  life  at  least,  with  the  elaboration  of 
nutritive  matter,  which  is  to  be  reintroduced  into  the  circulating  cur- 
rent. Its  elementary  structure  may  be  best  understood  from  the 
simple  form  it  presents,  when  it  is  first  capable  of  being  distinguished 

•in  the  embryo.  It  then  consists  of  a  single  tube,  closed  at  both  ends, 
and  filled  with  granular  matter ;  and  its  subsequent  development  con- 
sists in  the  lateral  growth  of  branching  off-shoots  from  this  central 
tubular  axis.  In  its  mature  state,  therefore,  it  consists  of  an  assem- 
blage of  glandular  follicles,  which  are  surrounded  by  a  plexus  of  blood- 
vessels ;  and  these  follicles  all  communicate  with  the  central  reservoir, 
from  which,  however,  there  is  no  outlet.  The  cavities  of.  the  follicles 
contain  a  fluid,  in  which  a  number  of  corpuscles  are  found,  giving  it  a 
granular  appearance.  These  corpuscles  are  for  the  most  part  in  the 
condition  of  nuclei;  but  fully  developed  cells  are  found  among  them,  at 
the  period  when  the  function  of  this  body  seems  most  active.  The 
chemical  nature  of  the  contents  at  this  period,  closely  resembles  that  of 
the  ordinary  proteine-compounds. — It  has  been  commonly  stated,  that 
the  Thymus  attains  its  greatest  development,  in  relation  to  the  rest  of 
the  body,  during  the  latter  part  of  foetal  life ;  and  it  has  been  considered 
as  an  organ  peculiarly  connected  with  the  embryonic  condition.  But 
this  is  a  mistake ;  for  the  greatest  activity  in  the  growth  of  this  organ 
manifests  itself,  in  the  Human  infant,  soon  after  birth ;  and  it  is  then, 
too,  that  its  functional  energy  seems  the  greatest.  This  rapid  state  of 
growth,  however,  soon  subsides  into  one  of  less  activity,  which  merely 
serves  to  keep  up  its  proportion  to  the  rest  of  the  body ;  and  its  increase 
usually  ceases  altogether  at  the  age  of  about  two  years.  From  that 
time,  during  a  variable  number  of  years,  it  remains  stationary  in  point 
of  size;  but,  if  the  individual  be  adequately  nourished,  it  gradually 
assumes  the  character  of  a  mass  of  fat,  by  the  development  of  the  cor- 
puscles of  its  interior  into  fat-cells,  which  secrete  adipose  matter  from 
the  blood.  This  change  in  its  function  is  most  remarkable  in  hyber- 
nating  Mammals ;  in  which  the  development  of  the  organ  continues, 
even  in  an  increasing  ratio,  until  the  animal  reaches  adult  age,  when  it 
includes  a  large  quantity  of  fatty  matter.  The  same  is  the  case,  gene- 
rally speaking,  among  Reptiles.  It  is  an  important  fact  in  the  history 
of  this  organ,  that  it  is  not  to  be  detected  in  Fishes ;  and  does  not 
appear  to  exist,  either  in  the  tadpole  state  of  the  Batrachian  reptiles, 
or  in  the  Perennibranchiate  group ;  so  that  we  may  regard  it  as  essen- 
tially connected  with  pulmonic  respiration.* 

512.  Various  facts  lead  to  the  conclusion,  that  the  function  of  the 
Thymus,  at  the  period  of  its  highest  development,  is  that  of  elaborating 
and  storing-up  nutritive  materials,  to  supply  the  demand  which  is  pecu- 
liarly active  during  the  early  period  of  extra-uterine  life.  -   The  elabo- 

*  See  Mr.  Simon's  admirable  Prize  Essay  on  the  Thymus  Gland. 


THYMUS   GLAND.  291 

rating  action  probably  corresponds  with  that,  which  is  exerted  by  the 
glands  of  the  Absorbent  system ;  and  the  product,  as  in  the  preceding 
cases,  seems  to  be  taken  back  into  the  circulation.  The  provision  of  a 
store  of  nutritive  matter  seems  a  most  valuable  one,  under  the  circum- 
stances in  which  it  is  met  with ;  the  waste  being  more  rapid  and  variable 
than  in  adults,  and  the  supply  not  constant.  Thus  it  has  been  noticed 
that,  in  over-driven  lambs,  the  thymus  soon  shrinks  remarkably ;  but 
that  it  becomes  as  quickly  distended  again  during  rest  and  plentiful 
nourishment.  As  the  demand  becomes  less  energetic,  and  as  the  sup- 
plies furnished  by  other  organs  become  more  adequate  to  meet  it,  the 
Thymus  diminishes  in  size,,  and  no  longer  performs  the  same  function. 
It  then  obviously  serves  to  provide  a  store  of  material,  not  for  the  nutri- 
tion of  the  body,  but  for  the  respiratory  process,  when  this  has  to  be 
carried  on  for  long  periods  (as  in  hybernating  Mammals,  and  in  Rep- 
tiles), without  a  fresh  supply  of  food. — It  is  possible  that  the  Thymus 
gland  may  further  stand  in  the  same  relation  to  the  Lungs,  as  the  Spleen 
to  the  Liver,  and  the  Supra-Renal  capsules  to  the  Kidneys ;  that  is,  as 
a  diverticulum  for  the  blood  transmitted  through  the  bronchial  arteries 
(which  are  the  nutritive  vessels  of  the  Lungs),  before  the  Lungs  acquire 
their  full  development  in  comparison  with  other  organs,  or  when  any 
cause  subsequently  obstructs  the  circulation  through  their  capillaries. 

513.  The  Thyroid  Gland  bears  a  general  analogy  to  the  Thymus ; 
but  its  vesicles  are  distinct  from  each  other,  and  do  not  communicate 
with  any  common  reservoir.  They  are  surrounded,  like  the  vesicles  of 
the  true  glands,  with  a  minute  capillary  plexus ;  and  in  the  fluid  they 
contain,  numerous  corpuscles  are  found  suspended,  which  appear  to  be 
cell-nuclei,  in  a  state  of  more  or  less  advanced  development.  This  body 
is  supplied  with  arteries  of  considerable  size ;  and  with  peculiarly  large 
lymphatics.  Though  proportionably  larger  in  the  foetus  than  in  the 
adult,  it  remains  of  considerable  size  during  the  whole  of  life. — It  ap- 
pears, from  the  recent  inquiries  of  Mr.  Simon,*  that  a  Thyroid  glancf^ 
or  some  organ  representing  it  in  place  and  office,  exists  in  all  Verte- 
brated  animals.  It  presents  its  simplest  form  in  the  class  of  Fishes ; 
in  some  of  which  it  appears  to  consist  merely  of  a  plexus  of  capillary 
vessels,  connected  with  the  origin  of  the  cerebral  vessels,  and  capable, 
by  its  distensibility,  of  relieving  the  latter,  in  case  of  any  obstruction 
to  the  proper  movement  of  blood  through  them.  In  the  higher  forms 
of  this  organ,  the  glandular  structure, — consisting  pf  the  closed  vesicles 
over  which  the  capillary  plexus  is  distributed,  and  of  their  cellular  con- 
tents,— is  superadded:  and  the  organ  then  appears,  like  the  Spleen,  to 
be  destined  for  two  diflferent  uses ;  namely,  to  serve  as  a  diverticulum 
to  the  Cerebral  circulation ;  and  to  aid  in  the  elaboration  of  nutritive 
matter,  which  is  probably  taken  up  by  the  Absorbent  system,  to  be 
again  poured  by  it  into  the  general  current  of  the  circulation. 

514.  Thus  the  Spleen,  the  Supra-Renal  Capsules,  the  Thymus  Gland,, 
and  the  Thyroid  Gland,  all  seem  to  share  in  the  preparation  of  the  nu- 
tritive materials  of  the  blood ;  in  fact,  we  may  regard  them  all  as  toge- 
ther constituting  an  elaborating  apparatus,  which  is  precisely  analogous 

*  Philosophical  Transactions,  1844. 


292  ABSORPTION  AND   SANGUIFICATION. 

to  that  of  the  ordinary  glands,  but  of  which  the  elementary  parts  are 
scattered  through  the  body  instead  of  being  collected  into  one  compact 
structure,  and  of  -which  the  product  is  received  back  into  the  blood,  in- 
stead of  being  discharged  through  an  eflferent  duct,  upon  the  surface, 
or  into  an  open  cavity,  of  the  body.  And  it  is  a  remarkable  confirma- 
tion of  this  view,  that  Prof.  Goodsir  should  have  ascertained  that  the 
last  three  of  these  organs  are  in  continuity  with  each  other,  during  the 
early  part  of  foetal  life ;  and  that  they  are  in  reality  portions  of  the 
hlastoderma  or  germinal  membrane  (chap,  xi.),  which  retain  their  ori- 
ginal simplicity  of  structure,  whilst  other  parts  undergo  changes  of  form 
and  texture,  and  which  continue  to  perform  their  original  function,  save 
that  the  materials  of  their  elaborating  action  are  now  supplied  by  the 
blood  instead  of  by  the  yolk.  The  probable  uses  of  these  bodies,  as 
diverticula  to  the  circulation  through  other  organs,  render  them  liable 
to  occasional  distension  with  blood ;  and  it  seems  determined  that  this 
blood  shall  not  lie  useless,  but  shall  be  subservient  to  the  action  in  ques- 
tion ;  the  gland-cells  that  line  the  cavities  of  the  organ  withdrawing  cer- 
tain constituents  of  the  blood,  to  restore  them  to  the  circulating  current, 
in  a  state  of  more  complete  preparation  for  the  operations  of  Nutrition. 
Their  function  is  very  probably  vicarious;  that  is,  the  determination  of 
blood  is  greatest  (through  the  state  of  the  other  organs),  at  one  time  to 
one  of  these  bodies,  and  at  another  time  to  another.  Hence  the  effects 
of  the  loss  of  any  one  of  them  are  not  serious ;  as  the  others  are  enabled 
in  great  degree  to  discharge  its  duty. 

4.   Composition  and  properties  of  the  Chyle  and  Lymph. 

515.  The  chief  chemical  difference  between  the  Chyle  and  the  Lymph, 
consists  in  a  much  smaller  proportion  of  solid  matter  in  the  latter,  and 
in  the  almost  entire  absence  of  fat,  which  is  an  important  constituent  of 
the  former.  This  is  well  shown  in  the  following  comparative  analyses, 
performed  by  Dr.  G.  0.  Rees,  of  the  fluids  obtained  from  the  lacteal 
and  lymphatic  vessels  of  a  donJiey,  previously  to  their  entrance  into  the 
thoracic  duct ;  the  animal  having  had  a  full  meal  seven  hours  before  its 
death. 

Water,  --.... 

Albuminous  matter  (coagulable  by  heat), 
•     Fibrinous  matter,  (spontaneously  coagulable), 

Animal  extractive  matter,  soluble  in  water  and  alcohol, 

Animal  extractive  matter,  soluble  in  water  only. 

Fatty  matter,        ------ 

Salts ; — Alkaline  chloride,  sulphate  and  carbonate,  with 
traces  of  alkaline  phosphate,  oxide  of  iron, 

100-000  100000 

The  Lymph  obtained  from  the  neck  of  a  horse  has  been  recently 
analyzed  by  Nasse,  with  nearly  the  same  result.  He  found  it  to  contain 
95  per  cent,  of  water ;  and  the  5  per  cent,  of  solid  matter  was  chiefly 
composed  of  albumen  and  fibrine,  with  watery  extractive, — scarcely  a 
trace  of  fat  being  discoverable.  The  proportions  of  saline  matter  were 
found  to  be  remarkably  coincident  with  those  which  exist  in  the  serum 


Chyle. 

Lymph. 

90-237 

95-536 

3-516 

1-200 

0-370 

0120 

0-332 

0-240 

1-233 

1-319 

3-601 

a  trace 

0-711 

0-585 

It 


CHARACTERS  OF  THE  CHYLE.  298 


of  the  blood  ;  as  might  be  expected,  from  the  fact,  that  the  fluid  portion 
of  the  lymph  must  have  its  origin  in  that  which  has  transuded  through 
the  blood-vessels:  the  absolute  quantity,  however,  is  rather  less.  A 
similar  analysis  of  the  Chyle  of  a  cat  by  Nasse,  has  given  results  very 
closely  correspondent  with  that  of  Dr.  Rees :  for  the  proportion  of 
water  was  90*5  per  cent. ;  and  of  the  9*5  parts  of  solid  matter,  the 
albumen,  fibrine,  and  extractive  amounted  to  more  than  5,  and  the  fat 
to  more  than  3  parts.  Dr.  Rees  has  also  analyzed  the  fluid  of  the 
Thoracic  duct  of  Man,  which  consists  of  chyle  with  an  admixture  of 
lymph ;  and  he  found  this  to  contain  about  90*5  per  cent,  of  water,  7 
parts  of  albumen  and  fibrine,  1  part  of  aqueous  alcoholic  extractive,  and 
not  quite  one  part  of  fatty  matter,  with  about  J  per  cent,  of  salines. 
The  composition  of  this  fluid  more  resembles  that  of  the  lymph  than  that 
of  the  chyle ;  the  proportion  of  the  fatty  to  the  albuminous  matter 
being  small.  This  was  probably  due  to  the  circumstance,  that  the  sub- 
ject from  which  it  was  obtained  (an  executed  criminal)  had  eaten  but 
little  for  some  hours  before  his  death. 

516.  The  characters  of  the  Chyle  are  not  the  same  in  every  part  of 
the  Lacteal  system ;  for  the  fluid  undergoes  a  very  important  series  of 
changes  in  its  characters,  in  its  transit  from  the  walls  of  the  intestines 
to  the  receptaculum  chyli.  The  fluid  drawn  from  the  lacteals  that  tra- 
verse the  intestinal  walls,  has  no  powet  of  spontaneous  coagulation; 
whence  we  may  infer  that  it  contains  little  or  no  Fibrine.  It  contains 
Albumen  in  a  state  of  complete  solution,  as  we  may  ascertain  by  the 
influence  of  heat  or  acid  in  producing  coagulation.  And  it  includes  a 
quantity  of  fatty  matter,  which  is  not  dissolved,  but  suspended  in  the 
form  of  globules  of  variable  size.  The  quantity  of  this  evidently  varies 
with  the  character  of  the  food ;  it  is  more  abundant,  for  instance,  in  the 
chyle  of  Man  and  the  Carnivora,  than  in  that  of  the  Herbivora.  It  is 
generally  supposed  that  the  milky  colour  of  the  chyle  is  owing  to  the 
oil-globules ;  but  Mr.  Gulliver  has  pointed  out  that  it  is  really  due  to 
an  immense  multitude  of  far  more  minute  particles,  which  he  has 
described  under  the  name  of  the  molecular  base  of  the  chyle.  These 
molecules  are  most  abundant  in  rich,  milky,  opaque  chyle ;  whilst  in 
poorer  chyle,  which  is  semi-transparent,  the  particles  float  separately, 
and  often  exhibit  the  vivid  motions  common  to  the  most  minute  mole- 
cules of  various  substances.  Such  is  their  minuteness,  that,  even  with 
the  best  instruments,  it  is  impossible  to  determine;  either  their  form  or 
their  dimensions  with  exactness ;  they  seem,  however,  to  be  generally 
spherical ;  and  their  diameter  may  be  estimated  at  between  l-36,000th 
and  l-24,000th  of  an  inch.  Their  chemical  nature  is  as  yet  uncertain  ; 
they  are  remarkable  for  their  unchangeableness,  when  submitted  to  the 
action  of  numerous  reagents,  which  quickly  afiect  the  proper  Chyle- 
corpuscles  ;  whilst  their  ready  solubility  in  Ether  would  seem  to  indi- 
cate that  they  are  of  an  oily  or  fatty  nature. 

517.  The  milky  aspect  which  the  serum  of  blood  sometimes  exhibits, 
is  due  to  an  admixture  of  this  molecular  base.  It  may  be  particularly 
noticed,  when  blood  is  drawn  a  few  hours  after  a  full  meal,  that  has  been 
preceded  by  a  long  fast.  By  recent  experiments  it  has  been  found,  that 
the  serum  begins  to  show  this  turbidity  about  half  an  hour  after  the 


294'  ABSORPTION  AND   SANGUIFICATION. 

meal  has  been  taken ;  and  that  the  turbidity  increases  for  some  hours 
subsequently,  after  which  it  disappears.  The  period  at  which  the  dis- 
coloration is  greatest,  and  the  length  of  time  during  which  it  continues, 
vary  according  to  the  digestibility  of  the  food.  When  the  serum  is 
allowed  to  remain  at  rest,  the  opaque  matter  rises  to  the  surface,  pre- 
senting very  much  the  appearance  of  cream;  and  when  separately 
examined,  it  has  been  found  to  contain  a  proteine-compound,  mingled 
with  oily  matter, — the  relative  amount  of  the  two  appearing  to  depend 
in  part  upon  the  characters  of  the  food  ingested.  Hence  it  would  seem 
probable  that  the  molecular  base  of  the  chyle  is  partly  derived  from 
albuminous  matter  of  the  food ;  more  especially  as  it  is  known  that  'oily 
particles,'  when  introduced  into  an  albuminous  fluid,  become  surrounded 
with  a  pseudo-membranous  pellicle.  The  gradual  disappearance  of  the 
turbidity  of  the  serum,  indicates  that  the  substance  which  occasioned  it 
no  longer  exists  as  such  in  the  circulating  current ;  being  either  drawn 
off  by  the  nutritive  or  secretory  operations,  or  being  converted  by  the 
assimilating  process  into  the  ordinary  constituents  of  the  blood. 

518.  During  the  passage  of  the  Chyle  along  the  lacteals,  towards  the 
Mesenteric  glands,  it  undergoes  two  important  changes ;  the  presence 
of  Fibrine  begins  to  manifest  itself  by  the  spontaneous  coagulability  of 
the  fluid ;  and  the  oil-globules  diminish  in  proportional  amount.  The 
fibrine  appears  to  be  formed  at  the  expense  of  the  albumen  ;  as  this 
latter  ingredient  undergoes  a  slight  diminution.  It  is  in  the  chyle 
drawn  from  the  neighbourhood  of  the  mesenteric  glands,  that  we  first 
meet  with  the  peculiar  floating  cells,  or  chyle-corpuscles,  formerly 
adverted  to  (§  214),  in  any  number.  The  average  diameter  of  these  is 
about  l-4600th  of  an  inch;  but  they  vary  from  about  l-7000th  to 
l-2600th, — that  is,  from  a  diameter  about  half  that  of  the  human  blood- 
corpuscles,  to  a  size  about  one-third  larger.  This  variation  probably 
depends  in  great  part  upon  the  period  of  their  growth.  They  are  usually 
minutely  granulated  on  the  surface,  seldom  exhibiting  any  regular  nuclei, 
even  when  treated  with  acetic  acid ;  but  three  or  four  central  parti- 
cles may  sometimes  be  distinguished  in  the  larger  ones.  These  corpus- 
cles are  particularly  abundant  in  the  chyle  obtained  by  puncturing  the 
mesenteric  glands  themselves ;  and  there  can  be  little  doubt,  that  they 
are  identical  with  the  altered  epithelium-cells,  which  line  the  lacteal 
tubes  in  their  course  through  those  bodies  (§  496). 

519.  The  glandular  character  of  these  cells,  and  their  continued  pre- 
sence in  the  circulating  fluid,  seem  to  indicate  that  they  have  an 
important  concern  in  the  process  of  assimilation, — that  is,  in  the  con- 
version of  the  crude  elements  derived  from  the  food,  into  the  organizable 
matter  adapted  to  the  nutrition  of  the  body;  in  other  words,  in  the 
conversion  of  Albumen  into  Fibrine ;  which  change  would  seem  to  take 
place  to  a  considerable  extent  in  the  Mesenteric  glands.  For  it  is  only 
in  the  Chyle  which  is  drawn  from  the  lacteals  intervening  between  the 
mesenteric  glands  and  the  receptaculum  chyli,  that  the  spontaneous 
coagulability  of  the  fluid  is  so  complete,  as  to  produce  a  perfect  sepa- 
ration into  clot  and  serum.  The  former  is  a  consistent  mass,  which, 
when  examined  with  the  microscope,  is  found  to  include  many  of  the 
chyle-corpuscles,  each  of  them  being  surrounded  with  a  delicate  film  of 


PROGRESSIVE   ELABORATION   OF   BLOOD.  295 

oil ;  the  latter  bears  a  close  resemblance  to  the  serum  of  the  blood  but 
has  some  of  the  chyle-corpuscles  suspended  in  it.  Considerable  diffe- 
rences present  themselves,  however,  both  in  the  perfection  of  the  coagu- 
lation, and  in  its  duration.  Sometimes  the  chyle  sets  into  a  jelly-like 
mass  ;  which,  without  any  separation  into  coagulum  and  serum,  liquefies 
again  at  the  end  of  half  an  hour,  and  remains  in  this  state.  The  coagu- 
lation is  usually  most  complete  in  the  fluid  drawn  from  the  receptaculum 
chyli  and  thoracic  duct ;  and  here  the  resemblance  between  the  floating 
cells,  and  the  white  or  colourless  corpuscles  of  the  blood,  becomes  very 
striking. 

520.  The  Lymph,  or  fluid  of  the  Lymphatics,  differs  from  the  Chyle, 
as  already  remarked,  in  its  comparative  transparency :  its  want  of  the 
opacity  or  opalescence,  which  is  characteristic  of  the  latter,  being  due 
to  the  absence,  not  merely  of  oil-globules,  but  also  of  the  "molecular 
base."  It  contains  floating  cells,  which  bear  a  close  resemblance  to 
those  of  the  Chyle  on  the  one  hand,  and'  to  the  colourless  corpuscles  of 
the  Blood  on  the  other ;  and  these,  as  in  the  preceding  case,  are  most 
numerous  in  the  fluid  which  is  drawn  from  the  lymphatics  that  have 
passed  through  the  glands,  and  in  that  obtained  from  the  glands  them- 
selves. Lymph  coagulates  like  chyle ;  a  colourless  clot  being  formed, 
which  encloses  the  greater  part  of  the  corpuscles.  The  lacteals  may  be 
regarded  as  the  Lymphatics  of  the  intestinal  walls  and  mesentery; 
performing  the  function  of  interstitial  absorption,  as  well  as  effecting  the 
introduction  of  alimentary  substances  from  without.  During  the  inter- 
vals of  digestion,  they  contain  a  fluid,  which  is  in  all  respects  conform- 
able to  the  lymph  of  the  lymphatic  trunks. 

521.  Thus  by  the  admixture  of  the  aliment  newly  introduced  from 
without,  with  the  matter  which  has  been  taken  up  in  the  various  parts 
of  the  system,  and  by  the  preparation  which  these  undergo  in  their 
course  towards  the  thoracic  duct,  a  fluid  is  prepared,  which  bears  a 
strong  resemblance  to  blood  in  every  particular,  save  the  presence  of 
red  corpuscles.  Even  these  may  sometimes  be  found  in  the  contents 
of  the  thoracic  duct,  in  sufiicient  amount  to  communicate  to  them  a 
perceptible  red  tinge  ;  but  it  is  doubtful  whether  they  have  not  found 
their  way  thither  accidentally, — some  of  the  lymphatic  or  lacteal  trunks, 
which  have  been  divided  in  the  dissection  necessary  to  expose  the  duct, 
having  taken  up  blood  by  their  open  mouths,  and  rapidly  transmitted  it 
into  the  general  receptacle.  The  fluid  of  the  tjioracic  duct  may  be 
compared  to  the  blood  of  Invertebrated  animals ;  from  which  the  red 
corpuscles  are  almost  or  altogether  absent ;  but  which  contains  white 
or  colourless  corpuscles,  and  which  possesses  but  a  slight  coagulating 
power,  in  consequence  of  its  small  proportion  of  fibrine.  And  we 
hence  see,  why  these  animals  should  require  no  special  absorbent  sys- 
tem ;  since  the  blood-vessels  convey  a  fluid,  which  is  itself  so  analogous 
to  the  chyle  and  lymph  to  be  absorbed,  that  the  latter  may  be  at  once 
introduced  into  it,  without  injuring  its  qualities. 


296  ABSORPTION  AND   SANGUIFICATION. 

5.  Absorption  from  the  External  and  Pulmonary  Snrface. 

522.  Although  the  Mucous  Membrane  of  the  Alimentary  Canal  is 
the  special  channel  for  the  introduction  of  nutritive  or  other  substances 
into  the  system,  it  is  by  no  means  the  onli/  one.  The  Skin  covering 
the  body,  and  the  Mucous  Membrane  prolonged  into  the  Lungs,  are 
also  capable  of  absorbing  liquids  and  vapours,  and  of  introducing  them 
into  the  Circulation ;  although  they  serve  this  purpose  less  in  Man 
and  the  higher  animals,  than  in  some  of  the  lower.  Their  utility  in 
this  respect  is  best  shown,  when,  from  peculiar  circumstances,  the 
function  of  the  digestive  cavity  cannot  be  properly  performed ;  and 
when,  therefore,  the  system  has  been  more  than  usually  drained  of  its 
fluids,  and  stands  in  need  of  a  fresh  supply.  Thus  shipwrecked  sailors, 
and  others,  who  are  suffering  from  thirst,  owing  to  the  want  of  fresh 
water,  find  it  greatly  alleviated,  or  altogether  relieved,  by  dipping 
their  clothes  into  the  sea,  and  putting  them  on  whilst  still  wet,  or  by 
frequently  immersing  their  own  bodies.  In  a  case  of  dysphagia,  in 
which  neither  solid  nor  fluid  nutriment  could  be  introduced  into  the 
stomach,  the  patient  was  kept  alive  for  a  considerable  time,  and  his 
sufferings  greatly  alleviated,  by  the  administration  of  nutritive  clysters, 
and  by  the  immersion  of  his  body  in  a  bath  of  tepid  milk  and  water, 
night  and  morning.  Under  this  system,  the  weight  of  the  body,  which 
had  previously  been  rapidly  diminishing,  remained  stationary,  although 
the  amount  of  the  excretions  was  increased :  and  the  use  of  the  bath 
had  a  special  influence  in  assuaging  the  thirst,  which  was  previously 
distressing.  It  appeared  that  the  water  of  the  urinary  excretion, 
amounting  to  from  24  oz.  to  36  oz.  per  day,  must  have  been  entirely 
supplied  from  this  latter  source.  Again,  a  man  who  had  lost  nearly 
31bs.  by  perspiration,  during  an  hour  and  a  quarter's  labour  in  a  very 
hot  atmosphere,  regained  8  oz.  by  immersion  in  a  warm  bath  at  95°  for 
half  an  hour.  In  these  cases  it  appears  probable,  from  the  experiments 
already  noticed  (§  502),  that  the  Lymphatics,  rather  than  the  blood- 
vessels, are  the  chief  agents  in  the  absorbing  process  ;  not,  however, 
from  any  powers  peculiar  to  them,  but  merely  on  account  of  the  thin- 
ness of  their  walls,  and  their  very  copious  distribution  in  the  skin. 

523.  Absorption  may  also  take  place  from  an  atmosphere  saturated 
with  watery  vapour.  Of  this  we  have  a  very  curious  proof  in  the 
Frog ;  whose  urinary  bladder  (which  serves  as  a  sort  of  reservoir  for 
water)  has  been  observed  to  be  refilled,  after  having  been  emptied,  by 
placing  the  animal  in  an  atmosphere  loaded  with  watery  vapour. 
Numerous  instances  are  on  record  which  prove  that  such  absorption 
may  take  place  in  Man,  to  a  very  considerable  extent;  though  the 
proportion  introduced  through  the  Skin,  and  through  the  Lungs,  can- 
not be  exactly  ascertained.  The  ready  introduction  of  volatile  matter 
into  the  system,  through  the  latter  channel,  is  a  matter  of  familiar 
experience ;  thus  if  we  breathe  an  atmosphere  through  which  the 
vapour  of  turpentine  is  diffused,  it  soon  produces  the  characteristic 
odour  of  violets  in  the  urinary  secretion.  And  it  is  probably  in  this 
manner,  that  a  large  number  of  those  putrescent  miasmata  and  other 
zymotic  poisons  are  introduced,  which  are  such  fertile  causes  of  disease. 


COMPOSITION   OF   THE   BLOOD.  297 

6.    0/  the  Composition  and  Properties  of  the  Blood. 

524.  Having  traced  the  steps  by  which  the  Blood  is  elaborated,  and 
prepared  for  circulation  through  the  body,  and  having  (in  the  former 
part  of  the  volume)  inquired  into  the  characters  of  its  chief  consti- 
tuents, we  have  now  to  consider  the  fluid  as  a  whole,  to  study  the  usual 
proportions  of  these  constituents,  and  the  properties  which  they  impart 
to  it. 

525.  The  Blood,  whilst  circulating  in  the'  living  vessels,  may  be 
seen  to  consist  of  a  transparent,  nearly  colourless  fluid,  termed  Liquor 
Sanguinis;  in  which  the  Corpuscles,  to  which  the  blood  owes  its  red 
hue,  as  well  as  the  white  or  colourless  corpuscles,  are  freely  suspended 
and  carried  along  by  the  current.  On  the  other  hand,  when  the  blood 
has  been  drawn  from  the  body,  and  is  allowed  to  remain  at  rest,  a 
spontaneous  coagulation  takes  place,  separating  it  into  Clot  and  Serum. 
The  Clot  is  composed  of  a  network  of  Fibrine,  in  the  meshes  of  which 
the  Corpuscles,  both  red  and  colourless,  are  involved ;  and  the  Serum 
is  the  same  with  the  liquor  sanguinis  deprived  of  its  Fibrine.  When 
the  Serum  is  heated,  it  coagulates,  showing  the  presence  of  Albumen, 
And  if  it  be  exposed  to  a  high  temperature,  sufficient  to  decompose  the 
animal  matter,  a  considerable  amount  of  earthy  and  alkaline  Salts 
remains.  Thus  we  have  four  principal  components  in  the  Blood : — 
namely,  Fibrine,  Albumen,  Corpuscles,  and  Saline  matter.  In  the 
circulating  Blood  they  are  thus  combined : — 

Fibrine  '\ 

Albumen  l     In  solution,  forming  Liquor  Sanguinis. 

Salts  J 

Red  Corpuscles, — Suspended  in  Liquor  Sanguinis. 

But  in  coagulated  blood  they  are  thus  combined : — 

Fibrine  \     Crassamentum  or  Clot. 

Red  Corpuscles    j 

A  bumen  |     Regaining  in  solution,  forming  Serum. 

A  certain  amount  of  Serum,  however,  is  involved  in  the  Crassamentum ; 
and  can  only  be  separated  by  ^cutting  the  clot  into  thin  slices,  and 
carefully  washing  it. 

526.  The  components  of  the  Blood  may  be  separated,  and  their 
amount  estimated,  in  various  ways.  Thus,  if  fresh-drawn  blood  be 
continually  stirred  with  a  stick,  or  be  "whippied"  with  a  bunch  of 
twigs,  the  Fibrine  coagulates  in  the  form  of  strings,  which  adhere  to 
the  wood,  and  may  thus  be  withdrawn  ;  whilst  the  red  corpuscles  then 
remain  suspended  in  the  serum,  gradually  sinking  to  the  bottom  in 
virtue  of  their  greater  specific  gravity.  On  the  other  hand,  the  Red 
Corpuscles  may  be  separated,  in  those  animals  in  which  they  are^  large 
enough,  by  passing  the  blood  through  a  filter ;  having  previously  mingled 
with  it  some  substance  which  retards,  but  does  not  prevent  its  coagula- 
tion* (§  185).     The  liquor  sanguinis  is  thus  separated  from  the  blood- 

*  This  experiment  cannot  be  performed  with  Human  blood,  because  the  corpuscles 
are  small  enough  to  pass  through  the  pores  of  any  filter  that  allows  the  liquor  sanguinis 
to  permeate  it ;  but  it  answers  very  well  with  Frog's  blood. 


298  ABSORPTION  AND   SANGUIFICATION. 

discs :  and  the  former  coagulates,  whilst  the  blood-discs  are  retained 
upon  the  filter.  This  experiment  convincingly  proves,  that  the  act  of 
coagulation  is  not  due  to  the  red  corpuscles,  as  was  at  one  time  ima- 
gined.— The  ordinary  act  of  coagulation,  by  withdrawing  the  Fibrine 
and  Corpuscles,  makes  it  easy  to  estimate  the  proportion  of  Albumen 
and  of  Saline  matter  in  the  Blood,  when  due  allowance  is  made  for 
the  quantity  of  Serum  retained  in  the  Clot ;  and  the  relative  propor- 
tions of  these  may  be  determined,  by  evaporating  the  fluid,  so  as  to 
obtain  the  whole  amount  of  solid  matter  it  contains,  and  by  then  cal- 
cining the  residuum,  so  as  to  ascertain  how  much  of  this  is  a  mineral 
ash, — the  remainder  being  chiefly  Albumen. — The  solid  matter  of  the 
blood  also  contains  various  Fatty  substances,  which  may  be  removed 
from  it  by  ether.  Some  of  these  appear  to  correspond  with  the  con- 
stituents of  ordinary  Fat  (§  261) ;  whilst  another  contains  phosphorus, 
and  seems  allied  to  the  peculiar  fatty  acids  of  Neurine  (§  383) ;  and 
another  has  some  of  the  properties  of  Cholesterine,  the  fatty  matter  of 
the  Bile  (§  724). — Besides  these,  there  are  certain  substances  known 
under  the  name  oi  Extractive ;  one  group  of  which  is  soluble  in  water, 
and  another  in  Alcohol.  Of  the  precise  nature  of  these,  little  isknown. 
They  have  been  aptly  termed  "ill-defined"  animal  principles ;  and  it  is 
probable  that  they  may  include  various  substances  in  a  state  of  change 
or  disintegration,  which  are  being  eliminated  from  the  Blood  by  the 
processes  of 'Excretion. 

527.  The  general  result  of  numerous  recent  analyses  of  the  Blood 
may  be  thus  stated.  The  whole  amount  of  solid  matter  is  rather 
greater  in  the  Male  than  in  the  Female ;  being,  on  the  average,  about 
210  parts  in  1000  in  the  former,  and  200  in  the  latter.  This  diff'e- 
rence,  however,  chiefly  depends  on  the  larger  proportion  of  red  corpus- 
cles contained  in  the  blood  of  the  male.  The  proportion  of  Albumen 
seems  more  constant  than  that  of  the  other  constituents  of  Blood; 
seldom  varying  beyond  5  or  6  parts,  in  either  sex,  above  or  below  70  in 
1000.  The  quantity  of  Corpuscles  appears  liable  to  considerably 
greater  variation ;  the  superiority  on  the  side  of  the  Male,  however, 
being  very  strongly  marked  in  the  maximum  and  minimum,  as  well  as 
in  the  average.  We  may  regard  its  average  in  the  Male  as  about  132  in 
1000  parts  of  blood;  but  it  may  fall  to  110-5  parts,  without  the  health 
being  seriously  affected ;  whilst,  on  the  other  hand,  it  may  arise  to  186 
without  any  manifestation  of  disease.  In  the  Female,  its  average  may 
be  about  120  parts  in  1000  ;  but  it  may  fall  to  as  little  as  71*4,  and  may 
rise  to  167,  consistently  with  ordinary  health.  The  range  of  variation 
is  thus  much  greater  in  the  Female  than  in  the  Male  ;  the  minimum 
being  considerably  less,  in  the  former,  than  half  the  maximum :  whilst 
in  the  latter  it  is  much  more.  This  is  probably  due  in  part  to  the  fact, 
that  the  loss  by  the  Catamenial  discharge  may  produce  a  great  tempo- 
rary depression  in  the  proportion  of  the  Corpuscles.  The  average 
proportion  of  Fibrine  seems  to  be  no  more  than  2*5  in  the  Male ;  and 
though  it  may  rise  to  as  much  as  3-5  or  even  4,  without  disordering  the 
system,  it  does  not  seem  to  fall  below  2,  in  the  state  of  ordinary  health. 
The  average  in  the  Female  is  probably  about  2*3  ;  the  proportion  may 
rise  to  3,  or  fall  to  1*8 ;  but  the  variation  seems  less  considerable  in  the 


COMPOSITION   OF  THE   BLOOD.  299 

Female  than  in  the  Male. — Much  is  probably  yet  to  be  leal'ned,  regard- 
ing the  influence  of  different  kinds  of  food  recently  taken,  on  the  pro- 
portion of  these  constituents  of  the  blood ;  and  it  does  not  seem  unlikely, 
from  what  has  been  already  stated  (§  517),  that  the  quantity  of  fatty 
matter  is  especially  liable  to  variation,  in  accordance  with  the  amount 
contained  in  the  food,  and  the  time  which  has  elapsed  since  the  last 
meal. 

528.  The  Saline  constituents  of  the  blood,  obtained  by  drying  and 
incinerating  the  whole  mass,  usually  amount  to  between  6  and  7  parts 
in  1000.  More  than  half  of  their  total  quantity  is  composed  of  the 
Chlorides  of  Sodium  and  Potassium ;  and  the  remainder  is  made  up  of 
the  tribasic  Phosphate  of  Soda,  the  Phosphates  of  Lime  and  Magnesia, 
Sulphate  of  Soda,  and  a  little  Phosphate  and  Oxide  of  Iron.  Of 
these  the  chief  part  are  dissolved  in  the  Serum ;  but  the  Earthy  Phos- 
phates, which  are  insoluble  by  themselves,  are  probably  combined  with 
the  proteine-compourids  (§  175) ;  and  the  Iron  is  contained,  chiefly  or 
entirely,  in  the  red  corpuscles.  It  is  difficult  to  speak  with  certainty, 
from  the  examination  of  the  ashes  of  the  blood,  as  to  the  state  of  the 
saline  contituents  of  the  circulating  fluid.  Thus,  the  Serum  has  an 
alkaline  reaction ;  and  this  has  been  supposed  to  be  due  to  the  pre- 
sence of  alkaline  Carbonates.  Moreover,  the  presence*  of  the  Lactates 
of  potash  and  soda  seems  probable ;  for  it  is  certain  that  lactic  acid  is 
normally  introduced  into  the  blood,  and  is  also  eliminated  from  it; 
and  the  rapidity  with  which  the  lactates  are  removed  as  such,  or  are 
converted  into  carbonates,  seems  to  afford  a  sufficient  explanation  of 
the  difficulty  in  demonstrating  the  presence  of  this  acid  in  the  circu- 
lating fluid.  Although  the  ashes  of  the  entire  mass  of  blood  do  not 
effervesce  on  the  addition  6f  an  acid,  effervescence  takes  place,  when 
acid  is  added  to  the  ashes  of  the  Serum ;  showing  the  existence  in  it, 
either  of  alkaline  Carbonates,  or- of  Lactates  which  have  been  reduced 
to  the  state  of  Carbonates  by  incineration.  When  the  entire  mass  of 
blood  is  incinerated,  however,  enough  phosphoric  acid  is  produced  from 
the  phosphorized  fats,  to  neutralize  the  alkaline  carbonates,  and  thus  to 
prevent  their  presence  from  being  recognised.  The  alkaline  reaction  of 
the  blood,  however,  is  certainly  dependent  in  part  upon  the  presence  of 
the  tribasic  phosphate  of  soda,  which  appears  to  confer  upon  the  serum 
a  special  power  of  absorbing  carbonic  acid. 

529.  The  following  appear,  from  the  considerp^tions  stated  in  the  pre- 
ceding part  of  the  Volume,  to  be  the  chief  uses  of  the  principal  consti- 
tuents of  the  Blood,  in  the  general  economy.  The  Fibrine  is  the  material, 
which  is  most  completely  prepared  for  organization,  and  which  supplies 
what  is  requisite  for  the  nutrition  of  the  larger  proportion  of  the  solid 
tissues  of  the  body.  It  is,  therefore,  being  continually  withdrawn  from 
the  blood  by  the  nutritive  operations ;  and  the  demand  appears  to  be 
supplied,  in  part  by  the  influx  of  Fibrine  that  has  been  prepared  in  the 
Absorbent  system,  and  in  part  by  the  continued  transformation  of  Albu- 
men, which  takes  place  during  the  circulation  of  the  Blood.  If  a  proper 
amount  of  Fibrine  be  not  present  in  the  Blood,  its  physical  properties 
are  so  far  altered,  by  the  diminution  of  its  viscidity,  that  it  will  not 
circulate  through  the  capillaries  as  readily  as  before ;  a  certain  degree 


300  ABSORPTION   AND   SANGUIFICATION. 

of  viscidity  having  been  experimentally  found  to  be  favourable  to  the 
movement  of  fluid  through  glass  or  metallic  tubes  of  small  bore. — The 
Albumen  of  the  blood  is  the  raw  material,  at  the  expense  of  which  not 
only  the  Fibrine,  but  many  other  substances  are  generated  during  the 
nutritive  process.  All  the  Albuminous  compounds  of  the  Secretions, 
the  Horny  matter  of  the  Epidermic  tissues,  the  Gelatine  of  the  simple 
fibrous  tissues,  the  solid  materials  of  the  Red  Corpuscles,  and  other  sub- 
stances, may  be  regarded  as  almost  certainly  produced  by  the  transfor- 
mation of  the  Albumen  of  the  Blood :  and  a  continual  supply  of  this 
from  the  food  is  therefore  requisite,  to  preserve  the  due  proportion  in 
the  circulating  fluid. — The  Red  Corpuscles,  which  (it  will  be  remembered) 
are  almost  exclusively  confined  to  Vertebrated  animals,  appear  to  be 
more  connected  with  the  function  of  Respiration,  than  with  that  of 
Nutrition ;  and  the  stimulating  action  of  Arterial  blood,  especially  upon 
the  Muscular  and  Nervous  tissues,  appears  chiefly  to  depend  upon  their 
presence.  It  has  been  observed  in  particular,  that  their  presence  is 
more  efiectual  in  stimulating  the  heart's  action,  than  is  that  of  either 
of  the  other  constituents  of  the  blood.  In  addition  to  what  has  been 
already  stated  (§  219),  in  reference  to  their  continual  disintegration  and 
renewal,  it  may  be  mentioned,  that  when  the  blood  of  one  animal  was 
injected  by  Magendie  into  the  veins  of  another  having  discs  of  very 
different  size  and  form,- the  original  Red  Corpuscles  soon  disappeared, 
and  were  replaced  by  those  characteristic  of  the  species,  in  whose  veins 
the  fluid  was  circulating. 

530.  The  use  of  the  Saline  matter  is  evidently  in  part  to  prevent  de- 
composition in  the  circulating  Blood ;  but  also  to  supply  the  mineral 
materials,  requisite  for  the  generation  of  the  tissues,  and  entering  into 
the  composition  of  the  secretions.  It  is  by  the  saline  and  albuminous 
matters  in  conjunction,  that  the  specific  gravity  of  the  Liquor  Sanguinis 
is  kept  up  to  the  point,  at  which  it  is  equivalent  to  that  of  the  contents 
of  the  Red  Corpuscles  ;  and  it  is  only  in  this  condition,  that  the  forma- 
tion of  the  latter  can  duly  take  place.  The  Fatty  matters  of  the  blood 
are  evidently  derived  from  the  food,  either  directly,  or  by  a  transforma- 
tion of  its  farinaceous  ingredients  (§  430) ;  and  they  are  chiefly  appro- 
priated to  the  maintenance  of  the  combustive  process.  But  there  is 
reason  to  believe,  that  Oleaginous  matter  performs  a  most  important 
part  in  the  incipient  stages  of  Animal  nutrition  ;  and  that  its  presence 
is  not  less  essential  to  the  formation  of  cells,  than  is  that  of  the  albumi- 
nous matter  which  forms  their  chief  component,  all  nuclei  being  observed 
to  include  fatty  particles.  That  which  may  be  superfluous  is  either  de- 
posited in  the  cells  of  Adipose  Tissue,  or  it  is  eliminated  by  the  Liver, 
the  Sebaceous  follicles  of  the  Skin,  and,  in  the  female  when  nursing,  by 
the  Mammary  glands. 

531.  The  proportion  of  these  components  of  the  Blood  is  liable  to 
undergo  changes  in  disease,  which  extend  far  beyond  the  widest  limits 
which  have  been  mentioned  as  consistent  with  health.  Thus,  the 
quantity  of  Fibrine  exhibits  a  remarkable  increase  in  Inflammation  ;  the 
amount  then  found  in  the  blood  being  from  5  or  6  parts  in  1000  to  9, 
10,  or  even  lOJ,  according  to  the  extent  and  intensity  of  the  disease. 
On  the  other  hand,  it  presents  a  remarkable  diminution  in  Typhoid 


COMPOSITION   OF   BLOOD   IN  DISEASE.  301 

fevers ;  the  quantity  being  sometimes  as  little  as  0-9.  If  any  decided 
Inflammation  should  develope  itself,  however,  in  the  course  of  the  Fever, 
the  proportion  of  Fibrine  rises  accordingly.  A  deficiency  of  Fibrine  in 
the  blood  predisposes  to  Haemorrhages,  Congestions,  &c.,  either  into 
the  substance  of  the  tissues,  or  on  the  surface  of  membranes ;  and  these 
conditions  are  well  known  to  be  of  frequent  occurrence  as  complications 
of  febrile  disorders.  An  excess  of  Fibrine  is  not  much  affected  by 
copious  bleeding,  even  if  this  be  frequently  repeated;  but  there  is 
reason  to  think,  that  the  administration  of  Mercury  has  a  tendency  to 
restrain  its  production. 

532.  It  is  difficult  to  say  what  amount  of  Red  Corpuscles  should  be 
regarded  as  excessive  ;  since,  as  we  have  seen,  they  may  augment  to  a 
great  degree,,  without  disturbing  the  health.  When  they  are  present 
in  an  amount  much  above  the  average,  they  seem  concerned  in  pro- 
ducing the  condition  termed  Plethora;  which  marks  a  "high  condi- 
tion" of  the  system,  and  which  borders  upon  various  diseases,  espe- 
cially those  of  Congestion,  and  Haemorrhages.  To  these  a  peculiar 
liability  then  exists  ;  because,  although  the  proportion  of  Fibrine  in  the 
blood  is  not  absolutely  low,  it  is  low  in  reference  to  that  of  the  Red 
Corpuscles.  Plethoric  persons  do  not  seem  more  liable  to  Inflamma- 
tion, than  are  those  of  weakly  constitution.  The  quantity  of  the  Red 
Corpuscles  is  rapidly  diminished  by  frequent  bleeding ;  and  hence  it  is 
lowered  by  repeated  Haemorrhages.  On  the  other  hand,  it  is  speedily 
restored  to  its  usual  standard  under  the  influence  of  nutritious  diet,  if 
the  digestive  powers  have  not  been  too  much  weakened  to  make  use  of 
this. — The  proportion  of  Red  Corpuscles  undergoes  a  marked  diminu- 
tion in  various  forms  of  Anaemia ;  and  particularly  in  Chlorosis.  In 
severe  cases  of  this  latter  disease,  it  has  been  found  as  low  as  27  in 
1000 ;  and  it  not  unfrequently  sinks  to  40  or  50.  The  marked  influ- 
ence of  the  administration  of  Iron,  in  favouring  the  reproduction  of 
Red  Corpuscles,  has  been  already  noticed  (§  219). 

533.  The  proportion  of  Albumen  in  the  blood  seems  less  liable  to 
change,  except  in  the  condition  termed  Albuminuria,  in  which  a  large 
quantity  of  Albumen  appears  in  the  Urine.  When  this  condition  is 
permanently  established,  it  is-  indicative  of  the  existence  of  serious 
organic  disease  of  the  kidney ;  but  it  may  occur  for  a  short  time  under 
the  influence  of  simple  congestion  of  that  organ,  which  causes  an 
escape  of  the  Albuminous  part  of  the  blood,  together  with  the  water 
which  is  filtered  off  (as  it  were)  in  this  gland  (§  728).  Now  when 
Albuminuria  is  fully  established,  there  is  a  marked  diminution  in  the 
quantity  of  Albumen  in  the  serum  of  the  blood ;  and  this  diminution 
is  constantly  proportional  to  the  amount  of  Albumen  present  in  the 
Urine.— The  proportion  of  Saline  matter  appears  to  undergo  less  alter- 
ation in  disease,  than  that  of  the  other  constituents  of  the  Blood ;  and 
has  not  been  found  to  have  a  regular  correspondence,  either  in  the  way 
of  excess  or  diminution,  with  any  particular  morbid  state. 

534.  The  condition  of  the  Blood  may  be  affected,  not  merely  by 
alteration  in  the  proportions  of  its  normal  ingredients,  but  by  the  pre- 
sence of  other  substances ; — either  such  as  are  generated  in  it,  and  are 
constantly  being  eliminated  from  it  in  health,  but  have  accumulated  to 


302 


ABSORPTION  AND   SANGUIFICATION. 


an  abnormal  degree ; — or  such  as  have  found  their  way  into  it  from 
without.  Thus,  Carbonic  Acid,  Urea  and  Lithic  Acid,  Cholesterine 
and  other  elements  of  Bile,  and  other  matters  which  it  is  the  office  of 
the  Excreting  organs  to  remove,  may  accumulate  in  the  blood,  and 
may  become  fertile  sources  of  disease,  by  their  injurious  influence. 
The  introduction  of  various  Mineral  substances,  by  absorption  from 
without,  changes  the  composition  of  the  normal  elements  of  the  Blood, 
and  thus  affects  their  vital  properties ;  thus  strong  saline  solutions 
diminish  or  destroy  the  coagulating  power  of  the  Fibrine.  But  the 
most  remarkable  cases  of  depravation  of  the  Blood,  by  the*  introduc- 
tion of  matters  from  without,  are  those  which  result  from  the  action  of 
ferments^ — exciting  such  Chemical  changes  in  the  constitution  of  the 
fluid,  that  its  whole  character  is  speedily  changed,  and  its  vital  pro- 
perties are  altogether  destroyed.  Of  such  an  occurrence  we  have  a 
marked  example  in  the  various  forms  of  malignant  fevers ;  in  which 
the  introduction  of  a  very  minute  quantity  of  noxious  matter  into  the 
blood,  either  through  the  lungs  or  through  the  skin,  produces  a  speedy 
alteration  in  the  characters  of  the  whole  mass  of  the  blood,  the  func- 
tion of  every  organ  in  the  body  is  disordered,  and  decomposition  of 
the  solids  and  fluids  takes  place  to  a  considerable  extent,  even  before 
the  circulation  ceases,  and  whilst  consciousness  yet  remains.  The 
train  of  symptoms  produced  by  the  bite  of  venomous  Serpents,  and  of 
rabid  animals,  appears  referable  to  the  same  cause, — the  alteration  in 
the  condition  of  the  whole  current  of  blood,  by  the  introduction  of  a 
minute  quantity  of  a  substance  that  acts  as  a  ferment. 

535.  The  Coagulation  of  the  blood,  as  already  explained,  depends 
upon  the  passage  of  its  Fibrine  from  the  fluid  state  to  the  solid  (§  184); 
consequently,  if  the  Fibrine  be  separated  from  the  other  elements,  no 
coagulation  takes  place.  On  the  other, hand,  if  the  amount  of  Fibrine 
be  larger  than  ordinary,  the  coagulum  possesses  an  unusual  degree  of 
firmness.  The  length  of  time  which  elapses  before  coagulation,  and 
the  degree  in  which  the  Clot  solidifies,  vary  considerably ;  in  general 
they  are  in  the  inverse  proportion  to  each  other.  Thus,  if  a  large 
quantity  of  blood  be  withdrawn  from  the  vessels  of  an  animal  at  the 
same  time,  or  within  short  intervals,  the -portions  that  last  flow  coagu- 
late much  more  rapidly,  but  much  less  firmly,  than  those  first  obtained, 
in  consequence  of  the  diminished  proportion  of  fibrine.  On  the  other 
hand,  when  the  fibrine  is  in  excess,  its  coagulation  is  unusually  de- 
layed. From  this  delay  an  important  change  results,  in  the  mode  in 
which  the  coagulation  takes  place ;  for  the  red  corpuscles,  instead  of 
being  uniformly  diffused  through  the  coagulum,  have  time  to  sink  to  the 
bottom,  in  virtue  of  their  greater  specific  gravity ;  and  the  upper  part 
of  the  clot  is  consequently  made  up  of  Fibrine,  almost  exclusively, 
whilst  the  lower  is  chiefly  formed  by  the  aggregation  of  the  red  cor- 
puscles. Hence  the  upper  layer  is  almost  destitute  of  colour  (whence 
it  has  received  the  name  of  huffy  coat),  and  is  remarkably  tenacious  in 
its  character ;  whilst  the  lower  is  very  deep  in  hue,  and  very  friable  in 
consistence.  When  the  fibrillated  network  forming  the  buffy  coat 
undergoes  the  slow  contraction,  which  is  characteristic  of  highly-elabo- 


COAGULATION  OF  BLOOD — BDFFY  COAT. 


303 


rated  fibrine  subsequently  to  its  coagulation,  it  draws  in  the  edges  of 
the  upper  surface  of  the  clot,  giving  it  a  cupped  appearance. 

536.  The  BufFy  Coat  may  present  itself  under  a  great  variety  of 
conditions ;  and  it  can  no  longer,  therefore,  be  regarded,  as  it  formerly 
was,  a  sign  of  the  Inflammatory  state.  It  is  most  fully  developed 
when  acute  Inflammation  exists  ;  because  in  that  condition  all  the 
circumstances  which  favour  it  are  present.  That  it  may  be  produced 
by  any  cause,  which  occasions  delay  in  the  coagulation  of  the  blood, 
is  evident  from  the  fact,  that  healthy  blood  may  be  made  to  exhibit  it, 
by  adding  a  solution  of  a  neutral  salt,  which  retards,  but  does  not 
prevent  its  coagulation.  But  the  blood  may  coagulate  with  its  ordinary 
rapidity,  or  even  more  speedily  than  usual ;  and  may  yet  exhibit  the 
Buffy  Coat.  And,  moreover,  the  separation  of  the  Fibrine  and  the 
Bed  Corpuscles  may  take  place  in  films  of  blood  so  thin,  as  not  to 
admit  of  a  stratum  of  one  being  laid  over  the  other ;  the  two  elements 
separating  from  each  other  laterally,  and  the  films  acquiring  a  speckled 
or  mottled  appearance,  equally  characteristic  of  the  Inflammatory  con- 
dition with  the  Buffy  Coat  itself.  Hence  the  separation  must  be  due 
in  such  cases,  to  other  causes  than  gravity :  and  recent  observations 
have  accounted  for  it,  by  showing  that  the  Red  Corpuscles  have  an 
unusual  attraction  for  one  another  in  the  inflammatory  state,  causing 
their  coalescence  in  piles  and  masses ;  whilst  the  particles  of  Fibrine 
have  also  a  peculiarly  strong  attraction  for  each  other.  Thus  there  is 
a  powerful  tendency,  that  draws  together  the  components  of  each  kind, 
and  consequently  tends  to  separate  them  from  the  others  ;  and  when 
this  separation  takes  place,  the  difference  in  the  specific  gravity  of  the 

Fig.  87. 


The  microscopic  appearance  of  a  drop  of  blood  in  the  inflammatory  condition.  The  red  co'P^s^^f  .J,^ 
their  circular  form,  and  adhere  together;  the  white  corpuscles  remain  apart,  and  are  more  abundant  inan 
usual. 

two  elements  decides  their  respective  situations. — The  peculiar  ten- 
dency of  the  Red  corpuscles  to  unite,  in  the  Inflammatory  state,  serves 
to  distinguish  this  condition  even  in  a  single  drop  of  blood ;  and  it  is 
then  that  the  White  corpuscles  may  be  most  easily  distinguished,  as 
they  are  seen  apart  from  the  rest  of  the  mass,   having  no  tendency  to 


304  CIRCULATION   OF  NUTRITIVE   FLUID. 

unite  with  it.  In  fact,  the  white  corpuscles  are  not  found  in  company 
with  the  red,  in  the  ordinary  coagulum,  but  rather  with  the  fibrinous 
portion ;  and  when  they  are  peculiarly  abundant,  as  they  usually  are 
in  Inflammatory  blood,  they  may  form  a  considerable  proportion  of  the 
bufiy  coat. 

537.  The  Buffy  Coat  may  present  itself,  without  the  least  increase 
in  the  normal  quantity  of  Fibrine,  and  without  any  approach  to  the 
Inflammatory  state ;  simply  because  the  Fibrine  is  present  in  exces- 
sive amount,  in  relation  to  the  amount  of  Red  corpuscles,  the  latter 
being  much  below  their  usual  proportion.  Thus  in  severe  Chlorosis, 
the  huffy  coat  is  almost  as  strongly  marked,  as  in  the  severest  Inflam- 
mation ;  but  the  two  conditions  are  at  once  distinguished  by  the  rela- 
tive proportions  of  solid  matter  in  the  blood,  as  indicated  by  the  size 
of  the  Coagulum.  For  in  Chlorosis,  the  coagulum  is  very  small,  in 
consequence  of  the  reduced  proportion  of  Corpuscles,  and  is  almost 
invariably  found  floating  in  the  serum  ;  whilst  in  the  ordinary  Inflam- 
matory condition,  it  is  of  full  size,  frequently  adhering  to  the  side  of 
the  vessel. 


CHAPTER  VI. 

OF  THE  CIRCULATION  OF  THE  BLOOD. 

1.  Nature  and  Objects  of  the  Circulation  of  Nutrient  Fluid. 

538.  The  nutritive  fluid, — the  elements  of  which  are  thus  partly  taken 
up  and  prepared  by  the  Absorbent  system,  but  are  in  great  part  also 
imbibed  through  the  Blood-vessels  distributed  upon  the  walls  of  the 
digestive  cavity,  and  assimilated  by  the  liver  (§  493), — is  carried  into 
the  various  parts  of  the  system,  by  the  act  of  Circulation.  This  move- 
ment answers  various  purposes.  It  furnishes  all  the  tissues,  which  are 
to  derive  nutriment  from  the  Blood,  with  a  constantly-renewed  supply 
of  the  materials  which  they  severally  require ;  and  in  this  manner  it  is 
subservient  to  the  growth,  not  only  of  those  tissues  which  form  part  of 
the  solid  structure  of  the  body,  but  also  of  those  various  cells,  covering 
its  free  surfaces,  which  are  being  continually  cast  off"  and  renewed,  and 
which,  in  the  course  of  their  development,  separate  from  the  blood  the 
products  that  are  to  perform  ulterior  purposes  in  the  economy,  or  are 
to  be  removed  as  altogether  efftete.  Thus  the  Circulation  is  subservient 
to  the  functions  of  Nutrition  and  Secretion.  In  the  exercise  of  these 
functions,  diff'erent  materials  are  drawn  from  the  blood  by  the  several 
tissues  it  supplies.  Thus  the  nutrition  of  the  muscle  requires  fibrine ; 
that  of  the  nerve  requires  fatty-matter ;  that  of  the  bone  draws  off"  gela- 
tine and  earthy  salts ;  that  of  the  hepatic  cells  removes  the  fatty  matter 
and  other  elements  of  bile;  that  of  the  milk-cells  (during  lactation) 
separates  albuminous,  fatty,  and  saccharine  substances ; — and  so  on. 
Thus  various  portions  of  the  blood,  when  returning  from  the  several 


CIRCULATION   OF   NUTRITIVE   FLUID.  305 

organs  through  which  they  have  been  transmitted,  have  undergone  very 
different  changes  by  the  nutritive  and  secreting  processes,  according  to 
the  function  of  the  organs  which  they  have  supplied ;  and  if  the  same 
portion  of  the  circulating  fluid  were  constantly  being  transmitted  to 
each  organ,  and  returned  from  it,  its  composition  would  speedily  undergo 
a  change  that  would  render  it  no  longer  fit  for  its  purposes.  By  the 
union  of  the  different  local  circulations,  however,  into  one  general  circu- 
lation, this  change  is  prevented,  and  the  whole  mass  of  the  blood  is 
maintained  in  its  normal  or  regular  condition;  for  as  its  composition  is 
such,  as  to  supply  all  parts  of  the  body,  in  a  state  of  health,  with  the 
proportions  of  nutritive  material  which  they  respectively  need ;  and  as 
the  returning  currents  are  all  mingled  together  in  the  vessels,  before 
being  again  distributed  to  the  system,  each  part  supplies  what  the  other 
has  been  deprived  of,  and  thus  the  normal  proportion  of  ingredients  in 
the  whole  mass  of  the  blood  is  constantly  kept  up,  whilst  in  each  of  its 
separate  streams  it  is  undergoing  an  alteration  of  a  different  kind. 

539.  But  these  processes  alone  might  be  carried  on  by  the  aid  of  a 
much  less  rapid  Circulation,  than  that  which  exists  in  Man  and  the 
higher  animals.  We  do,  in  fact,  occasionally  meet  with  examples  in 
which  they  continue  for  some  time,  under  an  almost  total  stagnation  of 
the  current.  There  are  others,  however,  which  require  a  much  more 
rapid  and  uninterrupted  movement  of  the  circulating  fluid.  We  have 
already  seen  that,  for  the  action  of  the  Nervous  and  Muscular  tissues, 
oxygen  is  necessary ;  and  the  amount  of  that  gas  contained  in  the  blood 
circulating  through  these  tissues  would  be  very  speedily  exhausted,  if  it 
were  not  continually  renewed ;  whilst  the  carbonic  acid,  which  is  formed 
at  the  expense  of  that  oxygen,  would  speedily  accumulate  to  an  injurious 
degree,  if  it  were  not  carried  off  as  fast  as  it  is  produced.  Hence  we 
find  that,  in  all  Animals,  the  maintenance  of  the  Respiration,  by  carry- 
ing Oxygen  from  the  respiratory  surface  into  the  different  parts  of  the 
system,  and  by  conveying  back  Carbonic  acid  to  be  thrown  off  at  the 
Respiratory  surface,  is  one  of  the  great  purposes  of  the  Circulation  of 
the  blood ;  and  its  extreme  importance  is  shown  by  the  very  speedy 
check,  which  the  interruption  of  this  function  produces  in  the  movement 
of  the  blood,  in  warm-blooded  animals.  Thus  in  a  Bird  or  Mammal, 
completely  cut  off  from  Oxygen,  the  circulation  in  the  lungs  will  come 
to  a  stop,  which  stoppage  will  necessarily  extend  itself  over  the  whole 
body,  in  little  more  than  three  minutes.  *  We  find,  then,  that  the  rate 
of  the  Circulation  in  different  animals  bears  a  relation  to  the  energy  of 
their  Respiration  ;  and  this  energy  is  closely  connected  with  the  general 
activity  of  their  functions,  but  particularly  with  that  of  the  Nervous  and 
Muscular  systems,  which  are  most  dependent  for  the  exercise  of  their 
powers  upon  a  continually  fresh  supply  of  oxygen,  and  upon  the  un- 
ceasing removal  of  the  carbonic  acid  which  is  generated  in  their  sub- 
stance. 

2.  Different  forms  of  the  Circulating  Apparatus. 

540.  It  is  desirable  that  the  Circulating  apparatus  should  be  first 
studied  in  its  very  simplest  form, — that  which  it  possesses  in  Plants  and 

20 


306  CIRCULATION   OF  NUTRITIVE   FLUID. 

in  the  lowest  tribes  of  Animals ;  as  in  this  way  alone  can  the  forces 
which  are  concerned  in  the  movement  of  the  fluid,  be  rightly  appre- 
ciated. In  all  the  higher  Plants,  the  ascending  or  crude  sap  is  to  be 
distinguished  from  the  elaborated  or  descending  sap.  The  former  of 
these  fluids  should  be  compared  rather  with  the  chyle  than  with  the 
blood  of  Animals ;  for  it  is  not  yet  fully  prepared  to  take  part  in  the 
nutrition  and  extension  of  the  structure.  But  there  are  some  circum- 
stances attending  its  movement,  which  throw  light  upon  other  more 
complicated  phenomena.  The  ascending  sap  consists  principally  of 
water;  which  is  imbibed,  together  with  various  substances  which  it 
holds  in  solution,  by  the  delicate  tissue  at  the  soft  extremities  of  the 
root-fibres,  or  spongioles.  The  power  of  forcing  upwards  a  column  of 
sap,  which  exists  in  these  bodies,  and  which  seems  due  to  Endosmose 
(§  491),  is  shown  by  very  simple  experiments.  If  the  stem  of  a  Vine, 
or  of  any  tree  in  which  the  sap  rises  rapidly,  be  cut  across  when  in  full 
leaf,  the  sap  continues  to  flow  from  the  lower  extremity ;  and  this  with 
such  force,  as  to  distend  with  violence,  or  even  to  burst,  a  bladder  tied 
firmly  over  the  cut  surface.  If,  instead  of  a  bladder,  a  bent  tube  be 
attached  to  this,  and  mercury  be  poured  into  it  so  as  to  indicate  the 
pressure  exerted,  it  is  found  that  the  rise  of  the  sap  takes  place  with  a 
force  equal  to  the  pressure  of  from  one  to  three  atmospheres  (from  15 
to  45  lbs.  upon  the  square  inch) — or  even  more.  Thus  the  ascent  of 
the  sap  is  partly  due  to  a  powerful  vis  a  tergo,  or  impelling  influence, 
derived  from  the  point  where  the  absorption  takes  place. 

541.  But,  on  the  other  hand,  if  the  upper  extremity  be  placed  with 
the  cut  surface  of  the  stem  in  water,  a  continued  absorption  of  that 
fluid  will  take  place,  as  is  evidenced  by  the  withdrawal  of  the  water 
from  the  vessel;  the  fluid  which  is  thus  taken  up,  however,  is  not 
retained  within  the  stem  and  branches,  but  is  carried  into  the  leaves, 
and  is  thence  dissipated  by  exhalation.  It  is  obvious,  then,  that  the 
vis  a  tergo  is  not  the  sole  cause  of  the  ascent  of  the  sap ;  but  that  a 
vis  afronte  also  exists,  by  which  the  fluid  is  drawn  towards  the  parts  in 
which  it  is  to  be  employed.  This  is  further  made  apparent  by  a  few 
simple  experiments.  If  a  branch,  when  thus  actively  absorbing  fluid, 
be  carried  into  a  dark  room,  the  absorption  and  ascent  of  fluid  imme- 
diately cease  almost  completely ;  and  are  renewed  again,  so  soon  as  the 
leaves  are  again  exposed  to  light.  Now  we  know,  from  other  experi- 
ments, that  light  stimulates  the  exhaling  process  (§  87),  whilst  darkness 
checks  it ;  and  the  cessation  of  the  demand  in  the  leaves  thus  produces 
a  cessation  in  the  absorption  at  the  lower  extremity  of  the  stem.  And 
this  is  the  case,  also,  in  the  natural  condition  of  the  plant ;  as  is  easily 
shown  by  immersing  the  roots  in  water,  and  observing  the  respective 
quantities  which  are  removed  by  absorption  during  sunshine,  shade,  and 
darkness.  On  the  other  hand,  the  movement  of  the  sap  may  be  excited, 
when  it  would  not  otherwise  take  place,  by  the  production  of  a  demand 
at  the  extremities  of  the  branches ;  thus  if  a  branch  of  a  vine  growing 
in  the  open  air,  be  introduced  into  a  hot-house,  and  be  subjected  to 
artificial  heat  during  the  winter,  its  buds  will  be  developed,  its  leaves 
will  expand,  and  these  will  draw  fluid  to  themselves  through  the  roots 
and  stems,  which  are  still  inactive  as  regards  the  remainder  of  the  tree. 


^^T5( 


CIRCULATION   OF  ELABORATED   SAP.  307 


nd  the  natural  commencement  of  the  movement  of  the  ascending  sap, 
which  takes  place  with  the  returning  warmth  of  spring,  has  been  ex- 
perimentally shown  to  occur,  in  the  first  instance,  not  in  the  neighbour- 
hood of  the  roots,  but  nearest  the  extremities  of  the  branches ;  the 
exhalation  of  fluid  from  the  expanding  buds  being  the  first  process, 
and  a  demand  for  fluid  being  thus  created,  which  is  supplied  by  the 
flow  that  is^  thus  excited  in  the  lower  part  of  the  stem, — this,  again, 
being  supplied  from  the  roots,  which  are  thus  caused  to  recommence 
their  absorbent  function. 

542.  Thus  we  see  that,  in  the  ascending  sap,  the  movement  is  en- 
tirely regulated  by  the  demand  for  fluid  occasioned  by  the  actions  of 
the  leaves ;  even  though  it  is  in  great  part  dependent  on  the  vis  a  tergo, 
which  has  its  seat  in  the  spongioles.  Not  even  this  force,  however,— 
powerful  as  it  has  been  shown  to  be, — can  produce  the  continuance  of 
the  upward  flow,  when  the  exhalation  from  the  leaves  is  checked  by 
darkness,  and  when  the  demand  occasioned  by  the  action  of  these  organs 
is  consequently  suspended. 

543.  The  movement  of  the  descending  sap  ofiers  numerous  points 
which  deserve  to  be  carefully  considered.  This  fluid  is  strictly  compa- 
rable to  the  blood  of  animals ;  having  undergone  a  preparation  or 
elaboration  in  the  leaves,  which  adapts  it  to  the  nutrition  and  extension 
of  the  structure,  and  to  the  formation  of  the  various  secretions  of  the 
plant.  A  great  part  of  the  fluid  of  the  ascending  sap  has  been  lost  by 
exhalation :  and  the  remainder,  thus  concentrated,  receives  a  large 
additional  supply  of  solid  matter  through  the  agency  of  the  green  cells 
of  the  leafy  parts,  which  take  in  carbon  from  the  atmosphere  (§  83) ; 
so  that  it  now  includes  a  considerable  amount  of  gummy  matter,  in  the 
state  prepared  for  being  converted  into  solid  tissue,  as  well  as  numerous 
other  compounds.  Now  this  elaborated  sap  seems  to  be  conveyed  into 
the  various  parts  of  the  system,  partly  by  transmission  from  one  cell  to 
another,  but  partly  through  the  agency  of  a  network  of  vessels,  which 
takes  its  origin  in  the  leaves,  and  extends  along  the  branches  to  the 
stem  and  roots,  chiefly  in  the  bark  of  those  parts.  These  vessels  are 
strictly  analogous  to  the  capillaries  or  small  blood-vessels  of  Animals ; 
but  they  difi*er  from  them  in  this, — that  the  capillary  network  of  Ani- 
mals communicates  on  either  side  with  larger  trunks,  being  formed,  in 
fact,  by  the  interlacement  or  anastomosis  of  their  minutest  branches, — 
whilst  the  network  of  nutritive  vessels  in  Plants  is  everywhere  con- 
tinuous with  itself,  not  having  any  communication  with  large  vessels,  so 
that  the  fluid  prepared  in  the  leaves  commences  a  circulation  there, 
which  is  continued  on  the  same  plan,  until  it  has  found  its  way  to  its 
remote  destination  in  the  roots. 

544.  The  natural  movement  of  the  elaborated  sap  through  these 
vessels  may  be  studied,  under  favourable  circumstances,  with  the  assis- 
tance of  the  microscope ;  the  requisite  conditions  being,  that  the  part 
should  be  sufiiciently  transparent  for  the  vessels  to  be  distinctly  seen, 
that  the  sap  shall  contain  globules  in  sufficient  number  to  allow  its 
movement  to  be  distinguished  by  their  means,  and  that  the  circulation 
should  be  observed  without  the  separation  of  the  organ  examined  from 
the  rest  of  the  Plant,  which  would  produce  irregular  movements,  by  the 


308  CIRCULATION   OF  NUTRITIVE   FLUID. 

escape  of  the  sap  from  the  wounded  part.  These  conditions  may  be 
attained  in  many  Plants  ; — most  conveniently,  perhaps,  in  the  stipules  of 
the  Fieus  elastica,  one  of  the  trees  which  affords  the  largest  supplies  of 
Caoutchouc;  and  it  is  then  found  that  the  movement  takes  place  in 
the  following  manner.  Distinct  currents  are  seen,  passing  along  the 
straightest  and  most  continuous  vessels,  and  crossing  by  the  lateral 
connecting  branches  of  the  network.  These  currents  follow  no  deter- 
minate direction ;  some  proceeding  up,  and  others  down ;  some  to  the 
left,  and  others  to  the  right ;  not  unfrequently  a  complete  stoppage  is 
seen  in  one  or  more  of  the  channels,  without  any  obvious  obstruction ; 
and  the  movement  then  recommences,  perhaps  in  the  opposite  direction. 
The  influence  of  a  force,  developed  by  the  act  of  circulation,  which 
determines  the  direction  of  the  movement,  appears  from  this :  that  if  a 
tube  be  cut  off,  so  as  to  give  its  contents  an  equally  free  exit  at  both 
ends,  the  sap  only  flows  out  at  one  extremity.  The  movement  is 
retarded  by  lowering  the  temperature  of  the  surrounding  air,  and  it  is 
completely  checked  by  extreme  cold ;  it  is  capable  of  being  renewed 
by  moderate  warmth ;  and  a  further  addition  of  heat  increases  its 
rapidity.  By  a  strong  electric  shock,  the  force  by  which  the  liquid  is 
propelled  seems  to  be  altogether  destroyed;  for  the  movement  then 
ceases  entirely. 

545.  Now  it  is  quite  certain  that  this  circulation  cannot  be  due  to 
any  vis  a  tergo  ;  both  because  it  is  not  constant  in  its  direction  in  par- 
ticular vessels ;  and  because  there  is  no  organ  in  which  any  propelling 
force,  that  could  extend  itself  through  such  a  complex  system  of  vessels, 
may  be  developed.  Nor  can  it  be  in  any  way  due  to  the  force  of  gravity ; 
for  although  this  may  assist  the  descent  of  the  fluids  through  the  stem, 
it  is  totally  opposed  to  its  ascent  from  the  ends  of  its  branches  towards 
their  origin,  when,  as  often  happens,  the  latter  are  at  the  higher  level. 
Moreover,  it  may  be  noticed  that  this  circulation  takes  place  most 
readily,  in  parts  that  are  undergoing  a  rapid  development ;  and  that  its 
energy  corresponds  with  the  vitality  of  the  part.  Further,  it  may  be 
observed  to  continue  for  some  time  in  parts  that  have  been  completely 
detached  from  the  rest ;  and  on  which  neither  vis  a  tergo,  nor  vis  a 
fronte,  can  have  any  influence.  It  is  evident,  then,  that  the  force, — 
whatever  be  its  nature, — by  which  this  continued  movement  is  kept  up, 
must  be  developed  by  the  processes  to  which  that  movement  is  subser- 
vient ;  in  other  words,  that  the  changes  involved  in  the  acts  of  nutrition 
and  secretion  are  the  real  source  of  the  motor  power.  The  manner  in 
which  they  become  so,  is  the  next  object  of  our  inquiry ;  and  on  this 
subject,  some  new  views  have  recently  been  put  forth  by  Prof.  Draper, 
which  seem  to  account  well  for  the  phenomena. 

546.  It  is  capable  of  being  shown,  by  experiments  on  organic  bodies, 
that,  if  two  liquids  communicate  with  each  other  through  a  capillary 
tube,  for  the  walls  of  which  they  both  have  an  affinity,  but  this  affinity 
is  stronger  in  the  one  liquid  than  in  the  other,  a  movement  will  ensue ; 
the  liquid  which  has  the  greatest  affinity  being  absorbed  most  energeti- 
cally into  the  tube,  and  driving  the  other  before  it.  The  same  result 
occurs  when  the  fluid  is  drawn,  not  into  a  single  tube,  but  into  a  net- 
work of  tubes,  permeating  a  solid  structure ;  for  if  this  porous  struc- 


CIRCULATION  IN   PLANTS   AND   LOWER  ANIMALS.  309 

ture  be  previously  saturated  with  the  fluid,  for  which  it  has  the  less 
degree  of  attraction,  this  will  be  driven  out  and  replaced  by  that  for 
which  it  has  the  greater  affinity,  when  it  is  permitted  to  absorb  this. 
Now  if,  in  its  passage  through  the  porous  solid,  the  liquid  undergo  such 
a  change,  that  its  affinity  is  diminished,  it  is  obvious  that,  according  to 
the  principle  just  explained,  it  must  be  driven  out  by  a  fresh  supply  of 
the  original  liquid,  and  that  thus  a  continual  movement  in  the  same 
direction  would  be  produced. 

547.  Now  this  is  precisely  that  which  seems  to  take  place  in  the 
organized  tissue,  permeated  by  nutritious  fluid.  The  particles  of  this 
fluid,  and  the  solid  matter  through  which  it  is  distributed,  have  a  certain 
affinity  for  each  other ;  which  is  exercised  in  the  nutritive  changes,  to 
which  the  fluid  becomes  subservient  during  the  course  of  its  circulation. 
Certain  matters  are  drawn  from  it,  in  one  part,  for  the  support  and 
increase  of  the  woody  tissue ;  in  another  part,  the  secreting  cells  demand 
the  materials  which  are  requisite  for  their  growth, — as  starch,  oil,  resin, 
&c. ;  and  thus  in  every  part  that  is  traversed  by  the  vessels,  there  are 
certain  affinities  between  the  solids  and  the  fluids,  which  are  continually 
being  developed  afresh  by  acts  of  growth,  as  fast  as  those  which  pre- 
viously existed  are  satisfied  or  neutralized  by  the  changes  that  have 
already  occurred.  Thus  in  the  circulation  of  the  elaborated  sap,  there 
is  a  constant  attraction  of  its  particles  towards  the  walls  of  the  vessels, 
and  a  continual  series  of  changes  produced  in  the  fluid,  as  the  result  of 
that  attraction.  The  fluid,  which  has  given  up  to  a  certain  tissue  some 
of  its  materials,  no  longer  has  the  same  attraction  for  that  tissue ;  and 
it  is  consequently  driven  from  it  by  the  superior  attraction  then  pos- 
sessed by  the  tissue  for  another  portion  of  the  fluid,  which  is  ready  to 
undergo  the  same  changes,  to  be  in  its  turn  rejected  for  a  fresh  supply. 
Thus  in  a  growing  part,  there  is  a  constantly-renewed  attraction  for  the 
nutritive  fluid,  which  has  not  yet  traversed  it ;  whilst,  on  the  other  hand, 
there  is  a  diminished  attraction  for  the  fluid,  which  has  yielded  up  the 
nutritive  materials  required  by  the  particular  tissues  of  the  part ;  and 
thus  the  former  is  continually  driving  the  latter  before  it. 

548.  But  the  fluid  which  is  thus  repelled  from  one  part,  may  still  be 
attracted  towards  another ;  because  that  portion  of  its  contents  which 
the  latter  requires,  may  not  yet  have  been  removed  from  it.  And  in 
this  manner,  it  would  seem,  the  flow  of  sap  is  maintained,  through  the 
whole  capillary  network,  until  it  is  altogether  exhausted  of  its  nutritive 
matter.  The  source  of  the  movement  is  thus  entirely  to  be  looked  for 
in  the  changes  which  take  place  in  the  act  of  growth  ;  and  the  influence 
of  heat,  cold,  and  other  agents,  upon  the  movement  is  exercised  through 
their  power  of  accelerating  or  retarding  those  changes. — The  fluid  which 
thus  descends  through  the  stem  and  roots,  seems  to  be  at  last  almost  en- 
tirely exhausted ;  a  portion  of  it  appears  to  find  its  way  into  the  interior 
of  the  stem,  and  to  be  mingled  with  the  ascending  current ;  but  all  the 
rest  seems  to  have  been  entirely  appropriated  by  the  difi'erent  tissues, 
through  which  it  has  circulated.  Thus  there  is  no  need  of  any  general 
receptacle,  into  which  it  may  be  collected,  and  from  which  it  may  take 
a  fresh  departure  ; — such  as  is  afi'orded  by  the  heart  of  Animals.  And 
as  the  purpose  of  this  circulation  is  only  to  supply  the  nutritive  mate- 


310  CIRCULATION  OF  NUTRITIVE  FLUID. 

rials,  and  not  to  convey  oxygen, — this  element  being  but  little  required^ 
in  the  vegetative  processes,  and  being  supplied  by  other  means, — the 
same  energy  and  rapidity  are  not  required  in  it,  as  need  to  be  provided 
for  in  the  higher  Animals. 

549.  A  condition  of  the  Circulating  system  very  similar  to  this,  exists 
in  several  of  the  lower  animals,  as  well  as  in  the  embryo-state  of  the 
higher.  In  the  very  lowest  no  blood-vessels  are  required,  for  the  same 
reason  that  no  sap-vessels  exist  in  the  lowest  Plants ; — namely,  because 
every  part  absorbs  and  assimilates  nutritious  fluid  for  itself,  so  that  it 
does  not  require  a  supply  from  vessels.  As,  in  the  sea-weeds,  the  whole 
substance  is  nourished  by  direct  absorption  from  the  fluid  in  contact 
with  the  external  surface,  every  part  of  which  seems  endowed  with  the 
same  absorbent  power,  so  in  Zoophytes  do  we  find,  that  the  whole  sub- 
stance is  nourished  by  direct  absorption  from  the  internal  surface, 
which  forms  the  lining  of  the  digestive  cavity.  In  the  same  manner, 
the  Aeration  of  the  animal  fluids, — or  the  exposure  of  them  to  the  air 
contained  in  water,  by  which  they  may  part  with  carbonic  acid  and 
imbibe  oxygen, — is  provided  for,  not  by  any  special  respiratory  organs, 
but  by  the  contact  of  water  with  every  part  of  the  soft  external  and 
internal  surfaces.  Further,  as  the  substance  of  their  body  is  nearly  of 
the  same  kind  in  every  part,  they  do  not  require  the  continual  inter- 
change of  the  fluid  distributed  to  its  several  portions.  Thus  no  circu- 
lation is  necessary,  in  these  simple  animals,  either  for  the  nutrition  of 
their  tissues,  or  for  the  aeration  of  the  fluids.  The  same  is  the  case 
with  others  of  the  lower  tribes  ;  as  well  as  with  the  embryo  of  the  higher 
Animals,  at  the  earliest  periods  of  their  development.  Thus  the  lowest 
JEntozoa,  or  parasitic  worms,  have  a  digestive  cavity  channelled  out,  as 
it  were,  in  their  soft  gelatinous  tissues ;  and  from  the  walls  of  this,  the 
nourishment  is  drawn  by  the  several  component  parts  of  those  tissues, 
without  the  mediation  of  vessels.  And  the  embryo  even  of  Man,  in  its 
early  condition,  consists  of  an  aggregation  of  cells,  each  of  which  absorbs 
for  itself  from  the  nutritious  fluid  with  which  it  is  surrounded,  and  goes 
through  all  its  functions  independently  of  the  rest. 

550.  Proceeding  a  little  higher,  we  find  the  first  appearance  of  proper 
vessels  in  the  higher  Untozoa,  and  in  the  Uchinodermata.  These  vessels 
take  up  the  nutritive  fluid  from  the  walls  of  the  digestive  cavity,  on 
which  they  are  spread  out,  just  as  the  roots  of  Plants  do  from  the  soil. 
They  then  unite  into  trunks,  by  which  the  fluid  is  conveyed  to  the  more 
distant  parts  of  the  structure,  in  the  same  manner  as  the  ascending  sap 
is  conveyed  to  the  leaves  by  the  vessels  of  the  stem  and  branches  ;  and 
these  trunks  again  subdivide,  and  form  a  network  of  capillary  vessels, 
which  are  dispersed  through  the  several  parts  of  the  fabric  ;  some  of  them 
being  very  abundantly  distributed  upon  a  portion  of  the  surface,  which 
is  particularly  destined  to  perform  the  respiratory  function.  Through 
these  capillary  vessels,  the  fluid  seems  to  move  in  very  much  the  same 
manner,  as  through  the  system  of  anastomosing  vessels  in  Plants  ; — that 
is,  its  motion  is  due,  rather  to  forces  which  are  developed  during  its 
circulation,  than  to  any  vis  a  tergo  derived  from  the  contractile  powder 
of  a  propelling  organ.  But  there  is  this  difl'erence :  that,  after  having 
traversed  the  minute  vessels,  and  yielded  up  to  the  tissues  a  part 


CIRCULATION  IN  ARTICULATED   ANIMALS.  311 

of  the  solid  matter  which  it  contains,  the  fluid  is  collected  again  by- 
other  trunks,  which  convey  it  back  to  the  point  from  which  it  started ; 
there  it  is  mingled  with  the  fluid  that  has  been  newly  absorbed,  and 
with  that  which  has  undergone  aeration ;  and  it  is  then  distributed,  as 
before,  through  the  general  capillary  network  of  the  body. 

551.  Now  this  is  very  much  the  condition  of  the  Human  embryo,  at 
the  time  when  vessels  are  first  developed  in  its  substance.  These  ves- 
sels are  formed  by  the  coalescence  of  cells ;  and  from  the  contents  of 
these  cells,  which  have  been  imbibed  from  the  yolk,  the  first  blood  seems 
to  be  derived.  The  first  formation  of  blood-vessels  takes  place,  not  in 
that  part  of  the  embryonic  structure  which  is  to  be  developed  into  the 
perfect  animal,  but  in  a  membranous  expansion  from  it,  which  surrounds 
the  yolk,  and  which  answers  the  purpose  of  a  temporary  stomach.  A 
capillary  network  is  formed  in  a  limited  portion,  of  this  membrane, 
termed  the  vascular  area  (Fig.  88) ;  and  this  not  by  the  branching  of 

Fig.  88.  .^  ^■■ 


Vascular  area  of  Fowl's  egg,  at  the  beginning  of  the  third  day  of  incubation;— a,  a,  yolk;  h,  b,  b,  h,  venous 
sinus  bounding  the  area;  c,  aorta;  d,  punctum  saliens,  or  incipient  heart;  e,  e,  area pellucida ;  /,/,  arteries 
of  the  vascular  area;  g,  g,  veins;  h,  eye. 

larger  trunks,  these  trunks  being  subsequently  formed  by  the  reunion 
of  the  capillaries.  The  first  movement  of  the  blood  is  towards  the  cen- 
tral spot,  in  which  the  organs  of  the  permanent  structure  are  being 
evolved;  and  it  takes  place  before  the  incipient iieart  has  acquired  any 
muscularity,  so  that  it  must  be  quite  independent  of  any  contractile  force 
exerted  by  that  organ.  Here  too,  then,  we  perceive  that  the  circulation 
is  essentially  capillary  ;  and  that  it  is  sustained  by  forces  very  different 
from  those,  of  which  the  action  is  most  evident  to  us  in  the  higher 
animals. 

552.  As  we  ascend  the  animal  scale,  however,  we  find  that  provision 
is  made  for  a  more  regular  and  vigorous  Circulation  of  the  Blood,  than 
that  which  exists  in  the  lowest  classes.  Even  in  the  class  of  EcUno- 
dermata  (including  the  Star-fish  and  Sea-urchin),  a  portion  of  the  prin- 
cipal vessel  is  peculiarly  endowed  with  contractile  power ;  and  this  may 
be  seen  in  constant  pulsation,  like  the  heart  of  the  higher  animals, 
alternately  contracting,  to  propel  the  fluid  it  contains,  through  the  ves- 


312  CIRCULATION   OF   NUTRITIVE   FLUID. 

sels  that  issue  from  it,  and  then  dilating,  to  receive  a  fresh  supply  from 
the  vessels  that  pour  their  contents  into  it.  It  seems  quite  certain, 
however,  from  the  extent  of  the  vascular  system  of  these  animals,  that 
the  influence  of  such  a  pulsatile  cavity  must  be  quite  insufficient  to  keep 
up  the  movement  of  blood  through  it.  A  similar  provision  is  observable 
in  the  lower  tribes  of  Worms,  in  which  this  contractile  vessel  lies  along 
the  back ;  propelling  the  blood  forwards,  by  a  sort  of  peristaltic  move- 
ment, through  trunks  which  pass  out  at  its  anterior  termination ;  and 
receiving  it  again  after  it  has  circulated  through  the  system,  by  vessels 
which  enter  at  its  posterior  extremity.  In  the  higher  orders  of  Worms, 
in  the  Myriapoda  or  Centipede  tribe,  and  in  Insects,  we  find  this  dorsal 
vessel  divided  by  transverse  partitions  containing  valves,  into  separate 
cavities  which  answer  to  the  diff'erent  segments  of  the  body.  Each  of 
these  is,  to  a  certain  extent,  the  heart  of  its  own  segment,  receiving  and 
propelling  blood  by  trunks  which  open  into  it ;  but  they  all  participate 
in  the  more  general  circulation  just  described,  a  large  portion  of  the 
blood  being  poured  into  the  hindermost  segment,  transmitted  forwards 
from  cavity  to  cavity  through  the  valves  which  separate  them,  and  at 
last  propelled  through  trunks  that  issue  from  the  most  anterior  segment. 
In  some  instances  we  find  that  two  or  three  of  these  trunks,  on  either 
side,  pass  round  the  oesophagus,  and  reunite  below  it,  so  as  to  enclose 
it  in  a  sort  of  collar  *  and  they  form  a  main  trunk  by  this  union,  which 
runs  backwards  along  the  under  surface  of  the  body,  and  which  distri- 
butes the  blood  to  its  difi'erent  organs  by  lateral  branches.  These 
subdivide  into  a  capillary  network,  and  the  returning  vessels,  which 
originate  in  this  network,  pour  the  blood  w^hich  has  circulated  through 
it  into  the  posterior  cavity  of  the  dorsal  vessel. — Still  it  is  very 
evident  from  the  observation  of  the  circulation  in  those  transparent 
species  in  which  the  whole  process  can  be  distinctly  watched  under  the 
Microscope,  that  the  contractile  power  of  the  dorsal  vessel  is  far  from 
sufficient  of  itself  to  sustain  the  Circulation  ;  and  that  the  movement  of 
the  blood  through  the  capillary  network  is  in  part  due  to  forces  deve- 
loped during  its  progress,  being  often  retarded  or  accelerated  in  parti- 
cular spots,  without  any  visible  change  in  the  propelling  force  of  the 
central  organ.  Moreover,  the  blood,  during  some  part  of  its  course, 
almost  always  escapes  from  the  proper  vessels  into  lacunce  channelled 
among  the  tissues ;  and  over  its  flow  through  these,  no  central  impelling 
organ  can  have  much  influence. 

553.  In  most  of  these  animals,  there  are  distinct  organs  of  Respira- 
tion, confined  to  some  one  part  of  the  body ;  and  we  often  find  that  the 
vessels  which  convey  blood  to  them,  are  furnished  with  distinct  con- 
tractile portions,  like  so  many  supplementary  hearts,  for  the  purpose  of 
propelling  the  blood  through  them  more  energetically.  In  proportion 
as  we  ascend  the  series  of  Articulated  animals,  do  we  find  for  the  most 
part,  a  more  vigorous  and  regular  circulation,  both  for  the  nutrition  of 
the  system,  and  for  the  transmission  of  the  blood  through  the  respira- 
tory organs ;  but  there  is  an  exception  in  the  case  of  insects,  which 
deserves  special  notice.  In  this  class,  the  circulation  is  much  less  vigo- 
rous than  it  is  in  other  Articulated  animals  of  similar  complexity  of 
structure ;  though  it  might  have  been  anticipated,  that  the  extraordinary 


R 


CIRCULATION  IN   MOLLUSCS.  313 


activity  of  their  movements  would  necessitate  a  corresponding  rapidity 
in  the  circulating  current,  especially  for  the  purpose  of  conveying  an 
extraordinary  supply  of  oxygen  to  the  nervous  and  muscular  systems. 
But  this  is  provided  for  in  another  way ;  the  air  being  conveyed  to 
these  tissues  not  through  the  blood,  but  by  direct  transmission  through 
the  minute  ramifications  of  the  air-tubes  or  tracheae,  which  penetrate 
the  very  smallest  organs  of  the  body  (§1 .659). 

554.  The  condition  of  the  Circulating  apparatus  in  the  Embryo  of 
higher  animals,  at  a  period  a  little  advanced  beyond  that  just  alluded  to, 
presents  a  striking  analogy  with  that  last  described ;  for  the  heart,  at 
the  time  of  its  first  formation,  seems  like  a  mere  dilatation  of  the  princi- 
pal vascular  trunk,  having  thickened  walls,  in  which,  after  a  time,  mus- 
cular fibre  begins  to  be  developed,  and  the  contractile  power  manifests 
itself.  The  pulsation  of  this  heart,  however,  does  not  seem  to  extend 
its  influence  immediately  through  the  vascular  area ;  the  capillary  circu- 
lation in  which,  remains  for  some  time  in  great  degree  independent  of  it. 
There  is  no  resemblance  in  form^  however,  between  the  dorsal  vessel  of 
Insects,  and  the  incipient  heart  of  the  higher  animals ;  since  the  latter 
is  never  much  prolonged,  and  speedily  becomes  doubled  (as  it  were) 
upon  itself;  and  its  first  division  into  distinct  cavities  is  merely  for  the 
purpose  of  separating  its  receiving  portion,  or  auricle^  from  its  propelling 
portion,  or  ventricle.  But  the  general  condition  of  the  Circulating 
system  is  much  the  same  in  the  two  cases ;  and  it  is  further  alike  in 
this, — that  it  is  not  always  easy  to  show  that  the  vessels  have  distinct 
walls,  as  they  frequently  seem  like  mere  channels  excavated  in  the 
tissues. 

bb^.  We  may  next  turn  our  attention  briefly  to  the  condition  of  the 
Circulating  apparatus  in  the  Molluscous  classes,  which  has  lately  been 
found  to  present  some  very  peculiar  characters.  In  these  it  would 
seem  as  if  the  moving  power  were  more  concentrated  in  the  heart,  than 
in  the  preceding ;  for  this  organ  seems  no  longer  like  a  mere  dilatation 
of  the  vascular  trunk,  but  is  a  distinct  sac  with  muscular  walls,  usually 
having  at  least  two  cavities,  an  auricle  and  a  ventricle.  The  usual 
course  of  the  Circulation  is  the  following.  The  blood,  expelled  from 
the  ventricle  of  the  heart,  passes  along  the  main  systemic  artery,  or 
aorta ;  which  distributes  it  to  the  body  at  large.  It  is  then  collected 
again,  and  transmitted  to  the  respiratory  organs ;  in  which  it  is  exposed, 
either  to  the  air  contained  in  the  surrounding  water,  or  (in  the  terres- 
trial Molluscs)  more  directly  to  the  atmosphere ;  and  from  these  it  is 
returned  to  the  heart,  to  be  again  transmitted  to  the  system. — Thus  we 
see  that  the  heart  of  these  animals  receives  and  impels  aerated  blood ; 
and  that  its  ofiice  is,  to  send  that  blood  to  the  capillaries  of  the  general 
system.     Hence  it  may  be  called  a  systemic  heart. 

556.  The  blood,  in  the  first  part  of  its  course,  passes  through  dis- 
tinct vessels :  it  has  been  lately  shown,  however,  that  in  the  Molluscs 
in  general,  the  blood  which  has  passed  through  the  systemic  capillaries, 
and  is  on  its  way  to  the  respiratory  organs,  is  no  longer  thus  confined, 
but  that  it  meanders  through  passages  or  lacuncc^  which  are  channelled 
out  in  the  tissues,  and  which  even  communicate  freely  with  the  abdomi- 
nal cavity  in  which  the  viscera  lie;   so  that  their  whole  exterior  is 


314  CIRCULATION   OF   NUTRITIVE  FLUID. 

bathed  by  the  circulating  fluid.  It  is  perhaps  in  this  part  of  its  course, 
that  it  most  readily  takes  up  the  fresh  nutrient  materials,  which  have 
been  prepared  by  the  digestive  process,  and  which  would,  under  such 
circumstances,  find  their  way  with  comparative  facility  from  the  inner 
surface  of  their  walls,  to  the  outer. — After  being  thus  diffused,  in  its 
venous  or  carbonized  state,  through  the  substance  of  the  tissues  and 
through  the  visceral  cavity,  it  is  again  collected  into  distinct  trunks ; 
and  these  convey  it  to  the  respiratory  organs. — Now  although  it  cannot 
be  doubted,  that  the  impelling  power  of  the  heart  is  the  chief  cause  of 
the  movement  of  the  blood  through  the  systemic  vessels,  yet  it  would 
seem  impossible  to  suppose,  that  this  power  can  be  exerted  over  the 
unrestrained  currents,  in  which  it  is  diffused  through  the  body,  after 
passing  through  the  systemic  capillaries ;  and  it  can  scarcely  be  doubted, 
that  its  passage  through  the  capillaries  of  the  respiratory  organs  is  due 
to  the  power  which  is  developed  in  themselves,  under  the  conditions 
already  alluded  to. 

557.  There  is  a  very  curious  phenomenon  to  be  observed  in  the  cir- 
culation of  some  of  the  lowest  Molluscs;  namely,  the  continual  reversal 
of  the  course  of  the  current.  The  heart,  in  these  animals,  is  much  less 
perfectly  formed,  than  in  the  higher  tribes ;  and  seems  more  like  the 
mere  contractile  dilatation  of  the  principal  trunk,  which  is  the  sole 
representative  of  that  organ  in  the  Echinodermata.  The  circulating 
fluid  is  sometimes  transmitted  first  to  the  system ;  and,  after  being  dis- 
tributed to  its  different  parts  by  the  ramifications  of  the  main  artery, 
it  meanders  through  the  channels  excavated  in  its  tissues ;  and  then 
flows  towards  the  respiratory  surface,  after  passing  over  which,  it  re- 
turns to  the  heart.  But  after  a  certain  duration  of  its  flow  in  this 
direction,  the  current  stops,  and  then  recommences  in  the  contrary 
direction, — proceeding  first  to  the  respiratory  organs,  and  then  to  the 
system  in  general.  It  would  seem  as  if  in  this,  one  of  the  lowest  forms 
of  animals  possessing  a  distinct  Circulation,  the  central  power  were  not 
yet  sufficiently  strong,  to  determine  the  course  which  the  fluid  is  to 
take :  so  that  it  undergoes  continual  vacillations.  In  a  group  of  Com- 
pound Polypes,  to  which  this  class  of  Molluscs  has  many  points  of 
affinity,  there  is  a  movement  of  fluid  through  the  stem  and  branches, 
which  in  like  manner  continually  changes  its  direction.  This  move- 
ment, however,  can  scarcely  be  regarded  in  the  light  of  a  proper  Cir- 

oCulation;  since  the  tubes  in  which  it  occurs  are  in  direct  communication 
with  the  digestive  cavities  of  the  Polypes.  But  the  flow  seems  altogether 
independent  of  any  mechanical  propulsion ;  and  takes  place  most  ener- 
getically and  regularly  towards  parts  in  which  new  growth  is  going  on. 

558.  We  have  now  to  consider  the  chief  forms  in  which  the  Circu- 
lating apparatus  presents  itself  in  the  Vertebrated  classes ;  and  first  in 
that  of  Fishes.  We  have  here,  as  in  Molluscs,  a  heart  with  two  cavi- 
ties, an  auricle  and  a  ventricle ;  this  heart,  however,  is  not  placed  at  the 
commencement  of  the  systemic  circulation,  but  at  the  origin  of  the 
respiratory  vessels.  The  blood  which  it  receives  and  propels,  is  venous 
or  carbonized ;  this  is  transmitted  along  a  main  trunk,  which  speedily 
subdivides  into  lateral  branches  or'  arches ;  and  these  distribute  it  to 
the  fringes  of  gills,  that  hang  on  the  sides  of  the  neck.     By  the  action 


I 


i 


CIRCULATION   IN  FISHES. 


315 


Diagram  of  the  Circulating 
Apparatus  of  Fishes: — a,  the 
auricle ;  h,  the  ventricle ;  c,  the 


the  water  on  the  gills,  the  blood  is  aerated  in  its  passage  through  them ; 
and  it  is  then  collected  by  a  series  of  converging  vessels,  which  re- 
unite to  form  the  great  systemic  artery,  or  aorta. 
By  the  ramifications  of  this  artery,  the  blood,  now 
aerated,  is  distributed  through  the  system,  and 
nffords  the  requisite  nourishment  and  stimulation 
to  its  tissues.  Returning  from  the  systemic  capil- 
laries in  a  venous  state,  the  blood  of  the  head  and 
anterior  portion  of  the  body  finds  its  way  at  once 
into  the  great  systemic  vein,  or  vena  cava,  by 
which  it  is  conveyed  back  to  the  auricle  of  the 
heart ;  but  that  which  has  traversed  the  capillaries 
of  the  posterior  part  of  the  body,  and  of  the  ab- 
dominal viscera,  is  conveyed  by  a  distinct  system 
of  veins  to  the  liver  and  the  kidneys.  In  these 
organs,  the  veins  again  subdivide  into  a  network 
of  capillaries,  which  is  distributed  through  the 
secreting  structure,  and  which  serves  to  afibrd  to 
the  secreting  cells  the  materials  of  their  develop- 
ment. This  is  termed  the  portal  system  of  vessels. 
From  the  capillaries  of  the  liver  and  kidneys,  the 
.Diood  IS  nnaily  coUectea  by  the  hepatic  and  renal  trunk  supplying  the  branchial 
veins,  which  convey  it  into  the  vena  cava ;  where  ?e1urnf;gfrom%re'gmsis^co^^^ 
it  is  mingled  with  the  blood  that  has  not  passed  ^^g  t^o'^/tworttTh'ich 
through  those  organs,  and  is  thus  conveyed  to  the  distributes 'it  to  the  system; 

,  *='  o  ^  J  thence  it  is  collected,  and  re- 

neart.  turned  to  the  auricle,  by  the 

559.  The  heart  of  Fishes,  then,  belongs  to  the  -;--hich  unite  in  the  vena 
respiratory  circulation.      It  propels  venous  blood 

to  the  capillaries  of  the  gills,  in  which  it  is  aerated ;  returning 
from  these,  the  aerated  blood  is  transmitted  through  a  second  set 
of  capillaries,  those  of  the  system,  in  which  it  again  becomes  venous ; 
whilst  a  portion  of  this  blood  is  made  to  traverse  a  third  set  of  capil- 
laries, those  of  the  liver  and  kidneys,  before  it  is  again  subjected 
to  the  propelling  power  of  the  heart.  Now  as  the  heart,  instead  of 
being  stronger  than  it  is  in  animals  with  the  complete  double  circu- 
lation presently  to  be  described, — in  which  the  greater  part  of  the 
blood  propelled  by  it  only  traverses  one  set  of  capillaries,  and  never 
more  than  two, — is  much  weaker  in  proportion,  it  is  evident  that  here, 
too,  a  supplementary  power  must  exist,  by  which  the  flow  of  blood 
through  the  capillaries  is  aided,  and  on  which,  indeed,  the  portal  circu- 
lation must  greatly  depend. 

560.  An  extremely  interesting  aspect  of  the  circulating  apparatus  is 
presented  by  the  Amphioxus  or  Lancelot;  an  animal  which  presents  the 
general  form  of  a  Fish,  and  which  can  scarcely  be  referred  to  any  other 
group ;  but  in  which  the  characters  of  the  Vertebrated  series  are  de- 
graded (as  it  were)  to  the  level  of  the  lower  Molluscous  and  Vermiform 
classes.  The  blood,  which  is  white,  moves  through  distinct  vessels,  but 
there  is  no  proper  heart ;  and  the  vascular  trunks  present  several  dila- 
tations, in  difi'erent  parts,  which  have  muscular  walls,  and  show  con- 
tractile power.     Thus  the  circulation  is  carried  on,  not  through  the 


316  CIRCULATION   OF   NUTRITIVE   FLUID. 

agency  of  a  central  impelling  organ,  as  in  other  Fishes ;  but  by  a  power 
which  is  scattered  or  diffused  through  various  parts  of  the  system  of 
blood-vessels,  as  in  the  lower  Invertebrata. — The  respiratory  apparatus, 
also,  is  formed  upon  a  type  much  lower  than  that  of  Fishes ;  for  it  con- 
sists simply  of  a  dilatation  of  the  first  part  of  the  alimentary  canal,  or 
pharynx,  upon  the  walls  of  which  the  blood  is  distributed  in  divided 
streams,  its  cavity  being  filled  with  water,  which  serves  to  aerate  the 
blood.  This  is  precisely  the  type,  on  which  the  respiration  is  effected, 
in  those  lowest  Molluscs,  of  which  mention  has  just  been  made,  as  ex- 
hibiting alternations  in  the  direction  of  the  circulating  current  (§  557). 
In  other  respects,  however,  the  arrangement  of  the  vascular  system  in 
this  extraordinary  animal  corresponds  with  that  which  obtains  in 
Fishes. 

561.  It  is  requisite  that,  in  the  class  of  Fishes,  the  whole  of  the 
venous  blood  returned  from  the  system  should  pass  through  the  respi- 
ratory organs  before  being  again  transmitted  to  the  body ;  since  the 
aerating  action  of  the  small  quantity  of  air  diffused  through  the  water, 
would  otherwise  be  insufficient  for  its  renovation.     But  in  Bejytiles,  all 

of  which  breathe  air  during  their  adult  condition, 
the  case  is  very  different ;  for  if  the  whole  current  of 
their  blood  were  exposed  to  the  atmosphere,  before 
being  again  sent  to  the  body,  the  quantity  of  oxygen 
conveyed  into  the  tissues  would  be  too  great,  and 
would  have  an  over-stimulating  effect.  The  plan  of 
the  Circulation  is,  therefore,  differently  arranged  in 
Reptiles.  We  find  the  heart  to  consist  of  three 
cavities ;  two  auricles  and  one  ventricle.  From  the 
ventricle  issues  a  single  trunk,  which  speedily  sub- 
divides ;  some  of  its  branches  proceeding  to  the  lungs, 
and  others  to  the  body.  The  blood  which  is  trans- 
mitted through  this  trunk,  is  of  a  mixed  character, 
as  we  shall  presently  see ;  being  neither  fully  aerated, 
nor  yet  highly  carbonized.  It  contains  sufficient 
oxygen,  to  stimulate  the  nervous  and  muscular  sys- 
tems of  these  comparatively  inert  animals ;  whilst  it 
tionK'ptls-la^Tnlre"  ^Iso  coutaius  cuough  of  carbonic  acid,  to  require 
ventricle,    receiving   the  bciuff  cxposcd  to  the  atmosphcrc  through  the  medium 

aerated  blood  from  ^  the      „   ^p      , ^  „,        .  .        ^^   ^  -    t     ^  °  i   ^i  i 

pulmonary  auricle,  and  ve-  01  the  lungs.  The  blood  which  has  passcQ  tlirough 
temi^c  aSriciet^nd  p?opei-  the  systcmic  capillarics,  and  which  has  been  thereby 
lir!hTp:fmon\"y'fapm^^^^  rendered  completely  venous,  is  returned  to  one  of 
ries,  d,  and  part  to  the  sys-  the  auriclcs — the  systeinic — by  the  vena  cava.     On 

tenuc  capillaries,  e.  ,  i  i  i       i    "^i  i        i       i  .    i      i  ■,     ^  i 

the  other  hand,  the  blood  which  has  passed  through 
the  capillaries  of  the  lungs,  and  which  has  been  thereby  rendered  com- 
pletely arterial,  is  returned  through  the  pulmonary  vein  to  the  other 
auricle, — the  pulmonary.  Thus  one  of  the  auricles  exclusively  receives 
aerated,  and  the  other  carbonated  blood ;  and  as  both  pour  their  con- 
tents into  the  common  ventricle,  the  blood  w^hich  that  cavity  contains 
and  propels  is  of  a  mixed  character. 

562.  Various  modifications  of  this  form  of  Circulating  apparatus 
exist  in  the  different  groups  of  reptiles.     In  the  lowest  among  them, 


li 


CIRCULATION   IN   REPTILES.  317 


ich  breathe  permanently  by  gills  like  Fishes,  besides  possessing 
imperfectly-developed  lungs,  the  apparatus  exhibits  a  blending  of  both 
plans ;  for  a  small  portion  of  the  blood,  which  is  propelled  by  each 
contraction  of  the  ventricle,  passes  directly  to  the  lungs ;  the  principal 
part  of  it  being  at  once  distributed  to  the  gills,  as  in  Fishes.  After 
passing  through  these,  it  is  transmitted  to  the  general  system ;  and  on 
returning  thence,  in  a  completely  venous  state,  it  is  mingled  with  the 
blood  which  has  been  arterialized  in  the  lungs.  This  latter,  however, 
bears  so  small  a  proportion  to  the  rest,  that,  if  the  aeration  were  not 
partly  elFected  by  the  gills,  it  would  be  insufficient  for  the  wants  of  the 
animal.  The  tadpoles  of  the  common  Frog  and  Water  Newt,  as  well 
as  of  other  species  which,  like  them,  begin  life  in  the  general  condition 
of  Fish,  present  a  similar  condition  at  one  period  of  their  change.  At 
first,  the  w^hole  aeration  is  effected  by  means  of  gills,  the  lungs  being 
in  a  rudimentary  or  undeveloped  state ;  and  the  entire  circulation  is 
carried  on  as  in  Fishes,  the  pulmonary  vessels  being  scarcely  traceable. 
As  the  lungs  begin  to  be  developed,  however,  a  portion  of  the  blood  is 
sent  to  them ;  and  at  the  same  time,  communicating  passages  which 
previously  existed,  between  the  vessels  that  convey  blood  to  the  gills, 
and  those  that  return  it  from  them,  are  increased  in  size ;  so  that  a 
certain  proportion  of  the  blood  is  transmitted  to  the  system,  without 
having  passed  through  the  gills  at  all.  By  a  further  increase  in  the 
diameter  of  these,  the  whole  current  of  blood  takes  this  direction,  the 
gills  being  no  longer  serviceable ;  and  as,  .at  the  same  time,  the  lungs 
are  attaining  their  full  development,  the  aeration  which  they  effect  in 
the  blood  transmitted  to  them  becomes  sufficient,  and  the  whole  circula- 
tion is  thus  permanently  established  on  the  Reptilian  type. 

563.  On  the  other  hand,  among  the  higher  Reptiles,  we  find  the 
circulating  apparatus  presenting  approaches  to  the  form  it  possesses 
in  Birds  and  Mammals.  For  the  ventricle  is  divided,  more  or  less 
completely,  into  two  cavities,  one  of  which  propels  aerated  blood  to 
the  system,  whilst  the  other  transmits  venous  blood  to  the  lungs.  A 
certain  amount  of  mixture  of  arterial  and  venous  blood  always  takes 
place,  however,  either  in  the  heart  itself,  or  in  the  vessels;  so  that 
the  blood  which  the  body  receives  is  never  purely  arterial.  But  this 
mixture  is  sometimes  effected  in  such  a  manner,  that  pure  arterial 
blood  is  sent  to  the  head  and  anterior  extremities  ;  though  the  re- 
mainder of  the  body  receives  a  half-aerated  fluid.  This  is  accomplished 
in  the  Crocodile,  by  a  provision  very  similar  to  that  which  exists  in 
the  foetus  of  warm-blooded  animals,  (chap,  xi.)  The  portal  circulation 
in  Reptiles  is  carried  on  nearly  upon  the  same  plan  as  in  Fishes.  It 
receives  the  blood  from  the  posterior  extremities  and  from  the  tail, 
as  well  as  from  the  abdominal  viscera ;  and  this  blood  is  distributed  by 
the  portal  capillaries,  not  only  through  the  liver,  but  also  through  the 
kidneys,  although  the  latter  also  receive  arterial  branches  from  the 
aorta.  The  fact  that  the  kidneys  are  supplied  from  the  general  portal 
circulation  in  Fishes  and  Reptiles,  has  an  important  bearing  on  the 
difference  in  the  arrangement  of  their  own  vessels,  which  will  be  here- 
after shown  to  exist,  between  the  kidneys  of  these  animals  and  those  of 
Birds  and  Mammals  (§  728). 


318  CIRCULATION   OF  NUTRITIVE   FLUID. 

564.  In  the  warm-blooded  division  of  the  Vertebrated  series,  which 
includes  the  classes  of  Birds  and  Mammals,  we  find  the  whole  circu- 
lation possessed  of  a  greatly-increased  energy ;  but  the  distinguishing 
peculiarity  of  the  apparatus  in  these  animals,  is  that  conformation  of 
the  heart  and  vessels,  which  secures  a  complete  double  circulation  of 

„.     „-  the  blood ;  that  is,  which  provides  for  the  aeration 

^^*     *  of  every  particle  of  the  venous  blood  which  has  re- 

turned from  the  system,  before  it  is  again  sent  into 
the  tissues.  The  heart  may  be  regarded  as  con- 
sisting of  two  distinct  parts, — a  systemic  heart,  like 
that  of  the  Molluscs,  forming  its  left  side, — and  a 
respiratory  heart,  like  that  of  Fishes,  constituting 
its  right.  Each  of  these  parts  has  a  receiving 
cavity  or  auricle,  and  an  impelling  cavity  or  ven- 
tricle. The  cavities  of  the  two  sides  are  completely 
separated  from  one  another,  in  the  adult  state  at 
least ;  though  their  walls  are  united  for  economy  of 
material.  It  is  obvious  that  much  is  saved  in  this 
manner ;  since,  as  the  contractions  of  the  auricles 
and  of  the  ventricles  on  the  two  sides  occur  simul- 
taneously, the  pressure  of  blood  in  the  one  is  partly 
Diagram  of  the  Circulating  antagonized  bv  that  on  the  other,  wherever  it  acts 

Apparatus  in  Mammals  and  -P  n    .i      .    •  j.      i,    ^.i,  m,  •  x 

Birds:— a,  the  heart,  contain-  on  tuo  wali  that  IS  common  to  Doth.  Ihis  antago- 
idivS'nTTenru'sbboTiSo^  nism  is  not^  complete,  however ;  since  the  systemic 
the  right  auricle  d,  the  right  ventriclo  coutracts  with  far  greater  force  than  the 

ventricle  propelling  venous  i-ini 

blood  through  e,  the  puimo-  pulmouary ;   and  the  wall  between  them  must  be 

raS8o?the'iungs';  ^,^theTcVt  Capable  of  rosistiug  the  diiference  of  pressure  on 

Zof  fro'm'IhTpuiron?ry  its  two  sidos,  thus  occasioncd.     The  blood  which  is 

kft°vent1-ido''r  which °?o^  rotumed  from  the  system,  in  a  venous  state,  through 

pels  it,  through  'the  aorta,  i,  the  voua  cava  to  the  right  auricle,  and  which  is 

to  the    systemic  capillaries,  ,   ,        .,    .     ,       ,,  .    i*-".  ,    .    ,        .     .  n     i  i 

j,  whence  it  is  collected  by  pourod  by  it  luto  the  right  ventricle,  is  impelled  by 
Sthlt^kThroughtheve'^a  the  latter  through  the  capillaries  of  the  lungs, 
*=*'«'*•  where  it  undergoes  aeration.     Returning  thence,  in 

an  arterialized  state,  it  is  conveyed  into  the  left  auricle,  and  thence 
flows  into  the  left  ventricle ;  by  which  it  is  propelled  through  the  great 
systemic  artery  or  aorta,  and  through  its  ramifications  to  the  general 
system. 

565.  The  greater  part  of  the  blood,  which  has  been  rendered  venous 
by  passing  through  the  systemic  capillaries,  is  collected  by  the  systemic 
veins,  and  is  returned  directly  to  the  heart  through  the  vena  cava.  But 
a  portion  is  still  employed  for  the  distinct  circulation,  which  is  destined 
to  supply  the  materials  for  the  secreting  action  of  the  liver.  The 
blood  that  has  traversed  the  capillaries  of  the  walls  of  the  alimentary 
canal,  and  of  the  other  viscera  concerned  in  digestion,  is  collected  again 
by  the  converging  veins  into  a  large  venous  trunk,  the  vena  portoe^  by 
which  it  is  distributed  through  the  liver.  This  vessel,  although  formed 
by  the  convergence  of  veins,  and  conveying  venous  blood,  has  really 
the  character  of  an  artery  in  an  equal  degree ;  for  it  subdivides  and 
ramifies  after  its  entrance  into  the  liver,  so  as  to  form  a  network  of 
capillaries,  from  which  the  blood  is  again  collected,  and  thence  trans- 


CIRCULATION   IN   MAMMALS. 


319 


mitted  by  the  hepatic  vein  to  the  vena  cava.  Thus  that  portion  of 
blood  which  supplies  the  liver  with  the  materials  of  its  secreting  action, 
passes  through  two  sets  of  capillaries,  between  the  time  of  its  leaving 


Fig.  92. 


Lnatomy  of  the  Human  Heart  and  Lungs.  1.  The  right  ventricle;  the  vessels  to  the  right  of  the  figure 
!  the  middle  coronary  artery  and  veins ;  and  those  to  its  left,  the  anterior  coronary  artery  and  veins. 
2.  The  left  ventricle.  3.  The  right  auricle.  4.  The  left  auricle.  6.  The  pulmonary  artery.  6.  The  right 
pulmonary  artery.  7.  The  left  pulmonary  artery.  8.  The  remains  of  the  ductus  arteriosus.  9.  The  arch 
of  the  aorta.  10.  The  superior  vena  cava.  11.  The  right  arteria  innominata,  and  in  front  of  it  the  vena 
innominata.  12.  The  right  subclavian  vein,  and  behind  it  its  corresponding  artery.  13.  The  right  common 
carotid  artery  and  vein.  14.  The  left  vena  innominata.  15.  The  left  carotid  artery  and  vein.  16.  The  left 
subclavian  vein  and  artery.  17.  The  trachea.  18.  The  right  bronchus.  19.  The  left  bronchus.  20,  20. 
The  pulmonary  veins;  18,  20,  form  the  root  of  the  right  lung;  and  7, 19,  20,  the  root  of  the  left.  21. The 
superior  lobe  of  the  right  lung.  22.  Its  middle  lobe.  23.  Its  inferior  lobe,  24.  The  superior  lobe  of  the 
left  lung.    25.  Its  inferior  lobe. 

the  heart  and  its  return  to  it.  The  portal  circulation  in  Birds,  as  in 
Reptiles  and  Fishes,  receives  the  blood  from  the  posterior  part  of  the 
body,  and  from  the  extremities ;  but  the  portal  blood  is  only  conveyed 
to  the  liver ;  the  kidneys  being  supplied  by  the  renal  artery. 

566.  This  perfect  form  of  the  Circulating  apparatus  is  only  attained, 
in  the  warm-blooded  animal,  after  a  series  of  transformations,  which 
strongly  remind  us  of  the  permanent  forms  presented  by  the  vascular 
system  in  Fishes  and  Reptiles.  Thus  in  the  embryo  of  the  Chick  at 
about  the  60th  hour,  and  in  that  of  the  Dog  at  about  the  21st  day, 
the  curved  and  dilated  tube,  of  which  the  heart  previously  consisted 
(§  554),  is  found  to  be  distinctly  divided  into  an  auricle  and  a  ven- 
tricle. From  the  latter  originates  the  main  arterial  trunk,  which 
divides  into  four  pairs  of  lateral  branches ;  and  these  pass  round  the 
pharynx,  precisely  in  the  position  and  direction  of  the  arteries  of  the 
gills  of  Fishes.  They  do  not,  however,  distribute  the  blood  to  gill- 
tufts  ;  for  none  such  are  developed  in  the  embryo  of  the  warm-blooded 
animal:  but  they  meet  again  below  the  pharynx,  to  form  a  trunk, 
which  supplies  the  general  circulation.  Within  a  short  period,  how- 
ever, the  whole  plan  of  the  circulation  undergoes  a  change.  The  auricle 


■ 


320  CIRCULATION   OF   NUTRITIVE  FLUID. 

and  the  ventricle  are  each  divided  by  a  partition,  that  is  developed  in 
the  middle  of  the  heart;  and  thus  the  two  auricles  and  the  two  ven- 
tricles are  formed.  Whilst  this  is  going  on,  a  change  takes  place  also 
in  the  vessels  that  arise  from  the  heart ;  for  the  arterial  trunk,  that  was 
previously  single,  undergoes  a  division  into  two  distinct  tubes ;  one  of 
which  is  connected  with  the  left  ventricle,  and  becomes  the  aorta, 
whilst  the  other  originates  in  the  right  ventricle,  and  becomes  the  pul- 
monary artery.  Of  the  four  pairs  of  branchial  arches,  some  are  sub- 
sequently obliterated ;  whilst  others  undergo  changes  that  end  in  their 
becoming  the  arch  of  the  aorta,  the  right  and  left  pulmonary  arteries, 
and  the  right  and  left  subclavians. 

567.  The  muscular  power  of  the  heart  is  much  greater  in  the  warm- 
blooded than  in  the  cold-blooded  Yertebrata,  in  proportion  to  the 
extent  of  the  circulation  which  it  is  concerned  in  maintaining  ;  and  it  is 
evidently  destined  to  take  a  much  larger  share  in  the  propulsion  of  the 
fluid,  than  it  is  in  the  lower  tribes.  Many  Physiologists  indeed,  are 
of  opinion  that  the  movement  of  the  blood  is  entirely  due  to  the  action 
of  the  heart ;  and  this  view  appears  to  be  supported  by  the  results  of 
numerous  experiments  upon  the  circulation.  But  it  is  very  difficult,  if 
not  impossible,  to  make  experiments  that  shall  be  really  satisfactory 
upon  this  point ;  and  it  appears  safer  to  trust  to  the  "  experiments 
ready  prepared  for  us  by  Nature,"  as  Cuvier  termed  them, — namely, 
those  lower  forms  of  animated  being,  in  which  various  diversities  of 
structure  present  themselves,  and  in  which  we  can  study  the  regular 
and  undisturbed  effects  of  these.  Thus  we  have  seen  that,  in  Plants 
and  the  lowest  Animals,  which  have  no  central  impelling  cavity,  the 
movement  of  the  nutritive  fluid  is  entirely  dependent  upon  the  power 
that  is  diffused  through  the  network  of  vessels  in  which  it  circulates. 
As  we  ascend  the  series,  we  find  an  organ  of  impulsion  developed 
upon  a  certain  part  of  the  vascular  system,  whose  object  it  is  to  give 
increased  energy  and  regularity  to  the  movement.  And  ascending  still 
higher,  we  find  the  moving  power  gradually  concentrated,  as  it  were,  in 
this  organ ;  yet  it  is  not  altogether  withdrawn  from  the  capillary  net- 
work, as  we  shall  see  from  several  facts  to  be  presently  adduced.  The 
particular  actions  of  the  Heart,  the  Arteries,  the  Capillaries,  and  the 
Yeins,  will  now  be  considered  in  more  detail. 

3.  Action  of  the  Heart. 

^  568.  The  Heart  is  a  hollow  muscle,  endowed  in  an  eminent  degree 
with  the  property  of  irritability  ;  by  which  is  meant,  the  capability  of 
being  easily  excited  to  movements  of  contraction  alternating  with  relaxa- 
tion (§  347).  At  first  sight,  its  actions  seem  different  from  that  of  the 
muscles  which  are  called  into  action  by  the  impulse  of  the  will ;  for  in 
these  there  is  apparently  no  such  alternation,  the  state  of  contraction 
being  kept  up  as  long  as  the  will  operates.  But  it  has  been  already 
explained  that,  even  in  these,  the  individual  fibres  are  probably  in  a 
state  of  continual  alternation  of  contraction  and  relaxation,  during  their 
active  condition, — one  set  taking  up  the  action,  whilst  another  is  return- 
ing to  the  state  of  relaxation.    Hence  the  chief  peculiarity  in  the  Heart's 


JT 


MOVING   POWERS   OF   THE   CIRCULATION.  321 


action  consists  in  this, — that  the  whole  mass  of  fibres  of  each  division 
of  the  organ  contract  and  relax  together.  The  contraction  of  the  two 
ventricles  is  perfectly  synchronous,  as  is  that  of  the  two  auricles ;  but 
the  contraction  of  the  auricles  is  synchronous  with  the  dilatation  of  the 
ventricles,  and  vice  versa.  The  regularity  of  this  alternation,  however, 
is  somewhat  disturbed,  when  the  irritability  of  the  heart  is  becoming 
exhausted  ;  and  both  sets  of  movements  will  continue,  when  the  auricle 
and  ventricle  have  been  separated  from  one  another.  Their  regular  suc- 
cession, in  the  natural  state,  is  doubtless  in  part  due  to  the  fact,  that 
the  transmission  of  blood  from  the  auricle  into  the  ventricle,  by  the 
contraction  of  the  former,  is  the  stimulus  which  most  effectually  excites 
the  latter  to  contraction  ;  whilst  the  ventricle  is  contracting,  the  auricle, 
now  free  to  dilate,  is  distended  by  the  flow  of  blood  from  the  veins  that 
open  into  it ;  and  this  flow  stimulates  it  to  renewed  contraction,  just  at  the 
time  when  the  contraction  of  the  ventricle  has  been  completed,  and  its 
state  of  relaxation  enables  it  to  receive  the  blood  poured  in  through  the 
orifice  leading  from  the  auricles. 

569.  In  the  living  animal,  the  auricular  and  ventricular  movements 
mcceed  one  another  with  great  regularity ;  and,  when  the  circulation 

|is  proceeding  with  vigour,  scarcely  any  appreciable  pause  can  be  dis- 
jovered  between  the  different  acts.     The  contraction  or  systole  of  the 
.uricles  takes  place  precisely  at  the  same  moment  with  the  dilatation  or 
liastole  of  the  Ventricles ;  and,  as  soon  as  the  latter  are  full,  and  the 
former  are  empty,  the  diastole  of  the  Auricles  and  the  systole  of  the 
"^entricles,  immediately  succeed.     The  systole  of  the  Ventricles  occa- 
jions  the  propulsion  of  blood  into  the  arterial  system;  and  this  action 
[produces  the  pulse,  as  will  be  explained  hereafter.     And  it  also  corre- 
sponds with  the  impulse  or  stroke  of  the  heart  against  the  parietes  of 
[the  chest.     This  impulse  is  not  produced,  as  some  have  supposed,  by 
the  swinging  of  the  entire  heart  forwards  ;  but  by  the  peculiar  mode  in 
which  the  Ventricular  systole  takes  place.     In  the  contraction  of  its 
walls,  every  dimension  is  lessened ;  but  shortening  is  the  most  percep- 
tible change,  the  vertical  diameter  of  the  Ventricle  being  the  greatest. 
Owing  to  the  peculiar  spiral  disposition  of  the  fibres  of  the  heart,  its 
apex  is  not  simply  drawn  upwards  by  their  contraction,  but  it  is  made 
to  describe  a  spiral  movement,  from  right  to  left,  and  from  behind  for- 
wards ;  and  it  is  in  this  manner,  that  it  is  caused  to  strike  against  the 
side  of  the  chest.  ^ 

570.  The  systole  of  the  Ventricles  is  immediately  followed  by  their 
diastole  ;  but  the  commencement  of  this  has  been  observed  to  occur  at 
a  small  interval  previous  to  the  contraction  of  the  Auricles ;  and  some- 
times a  brief  interval  of  repose  may  be  noticed,  separating  i\iQ  first  stage 
of  the  Ventricular  diastole,  which  may  be  partly  due  to  the  simple  elas- 
ticity of  the  walls  of  the  Ventricles,  from  the  second,  which  is  accompa- 
nied by  the  systole  of  the  Auricles,  and  in  which  the  blood  of  the  latter 
is  forcibly  propelled  into  them.  When  the  circulation  is  being  carried 
on  regularly,  the  blood  is  propelled  into  the  Ventricles  with  sufficient 
force  to  dilate  them  strongly ;  so  that  the  hand  closed  upon  the  heart 
is  opened  with  violence.  Even  the  auricles  dilate  with  more  force  than 
it  seems  easy  to  account  for  by  the  vis  a  tergo  of  the  blood  in  the  venous 

21 


322  CIRCULATION   OF   NUTRITIVE  FLUID. 

system ;  whicli  is  small  compared  with  that  which  the  fluid  possesses  in 
the  arteries. 

571.  The  natural  movements  of  the  Heart  are  accompanied  by  cer- 
tain sounds,  which  are  heard  when  the  ear  is  applied  over  the  cardiac 
region ;  and  an  acquaintance  with  these  sounds  and  with  their  causes 
is  of  much  importance,  since  the  alterations  which  they  undergo  in  dis- 
ease, afiford  us  some  of  our  most  accurate  information  in  regard  to  the 
nature  of  the  morbid  affection.  Concurrently  with  the  impulse  of  the 
heart  against  the  chest,  a  dull  and  prolonged  sound  is  heard  ;  this, 
which  is  termed  the  first  sound,  marks  the  ventricular  systole,  and  is 
synchronous  with  the  pulsation  in  the  arteries.  The  second  sound, 
which  is  short  and  sharp,  follows  immediately  upon  the  conclusion  of 
the  first ;  and  it  must  therefore  be  produced  during  the  first  stage  of 
the  Ventricular  diastole,  before  the  systole  of  the  Auricles  has  com- 
menced. It  is  followed  by  a  brief  interval  of  repose,  which  occurs 
during  the  remainder  of  the  Ventricular  diastole  and  the  Auricular 
systole ;  and  this  is  succeeded  by  a  recurrence  of  the  first  sound.  If 
the  whole  period  between  two  successive  pulsations  be  divided  into  four 
parts,  it  is  estimated  that  the  first  sound  usually  occupies  two  of  these ; 
and  the  second  sound,  and  the  interval,  one  part  each. 

572.  Now  in  order  to  understand  the  causes  of  these  sounds,  it  is 
necessary  to  study  the  course  of  the  blood  through  the  heart  a  little 
more  in  detail.  When  the  Ventricles,  distended  with  blood,  are  con- 
tracting upon  their  contents,  they  eject  them  forcibly  through  the  narrow 
orifices  of  the  aorta  and  pulmonary  artery  ;  and  the  semilunar  valves, 
which  guard  these  orifices,  are  thrown  back  against  the  walls  of  the 
arteries.  The  regurgitation  of  the  blood  into  the  auricles  is  prevented 
by  the  action  of  the  mitral  and  tricuspid  valves ;  but  the  flaps  of  these 
do  not  suddenly  fall  against  each  other,  when  the  blood  first  begins  to 
press  them  together ;  being  restrained  by  the  chordce  tendinem.  The 
connexion  of  these  with  the  carnece  columnce,  which  form  part  of  the 
ventricular  walls,  and  contract  simultaneously  with  them,  appears  to 
have  this  use, — ^that  the  flaps  of  the  valves,  which  are  completely  thrown 
back  during  the  preceding  rush  of  blood  from  the  auricles  to  the  ven- 
tricles, may  be  drawn  into  a  favourable  position  for  the  blood  to  get 
behind  them  and  bring  them  together,  so  as  completely  to  close  the 
orifice.  As  soon  as  the  ventricular  diastole  begins  to  take  place  (even 
before  the  contraction  of  the  auricles  has  commenced),  there  will  be  a 
tendency  of  the  blood,  that  has  just  been  propelled  into  the  aorta  and 
pulmonary  artery,  to  flow  back  to  the  heart ;  but  this  regurgitation  is 
completely  prevented  by  the  semilunar  valves  of  these  orifices,  which 
are  immediately  filled-out  by  the  backward  tendency  of  the  blood,  and 
which  meet  in  such  a  manner  as  completely  to  close  the  orifices.  This 
closure  is  much  more  sudden  than  that  of  the  mitral  and  tricuspid  valves, 
being  altogether  unrestrained. 

573.  The  first  sound  is  certainly  in  part  due  to  the  impulse  of  the 
heart  against  the  thoracic  parietes ;  as  is  proved  by  the  fact,  that  when 
the  impulse  is  prevented,  the  sound  is  much  diminished  in  intensity ; 
also  by  the  circumstance,  that,  when  the  ventricles  contract  with  vigour, 
the  greatest  intensity  of  the  sound  is  over  the  point  of  percussion.    But 


i 


SOUNDS   OF   THE  HEART.  323 

that  it  is  not  entirely  due  to  this  cause,  is  also  sufficiently  evident  from 
two  circumstances ; — its  prolonged  character,  which  could  scarcely  be 
given  by  a  momentary  impulse; — and  its  continuance,  though  with 
diminished  intensity,  when  the  parietes  of  the  chest  are  wanting,  and 
even  after  the  complete  removal  of  the  heart  from  the  body.  Moreover, 
the  duration  of  the  first  sound  is  much  increased  by  any  morbid  state 
of  the  orifices  of  the  ventricles,  which  obstructs  the  exit  of  the  blood. 
Much  discussion  has  taken  place  as  to  the  cause  of  that  part  of  it,  which 
is  not  due  to  the  impulse  ;  some  having  attributed  it  to  the  muscular 
contraction  of  the  walls  of  the  ventricles,  others  to  the  flow  of  blood 
over  the  irregular  surfaces  of  their  interior,  and  others  to  the  rush  of 
the  fluid  through  the  narrow  orifices  leading  to  the  aorta  and  pulmonary 
artery.  There  can  be  little  doubt,  that  the  first  and  last  of  these  causes 
are  both  concerned  in  producing  the  sound.  For  as  a  sound  may  be 
distinctly  heard  by  means  of  the  stethoscope,  when  the  heart  is  con- 
tracting vigorously  out  of  the  body,  and  when  no  blood  is  propelled  by  it, 
nothing  else  than  muscular  contraction  can  be  then  regarded  as  its  source; 
d  there  is  other  evidence,  that  sound  may  be  produced  by  this  cause, 
ce  the  vigorous  contraction  of  any  other  large  muscle  gives  rise  to  a 
ntinued  tingling,  which  may  be  heard  through  the  stethoscope.  But 
hen  the  heart  is  contracting  in  its  natural  position,  and  is  propelling 
e  blood  with  its  ordinary  vigour,  the  sound  is  heard  in  its  greatest  in- 
ensity  at  the  hase  of  the  heart,  i.  e.,  at  the  origin  of  the  great  arteries ; 
and  since  any  obstruction  to  the  exit  of  the  blood  through  them  increases 
the  intensity  as  well  as  the  length  of  the  sound,  it  can  scarcely  be 
doubted  that  it  is  partly  due  to  the  rush  of  the  blood  through  the  con- 
tracted entrances  of  these  vessels.  A  very  similar  sound,  known  as  the 
"bruit  de  soufflet"  or  bellows-sound,  may  be  heard  through  the  stetho- 
scope, over  any  large  artery,  when  it  is  compressed,  so  as  to  permit  the 
passage  of  blood  less  readily  than  usual.  Thus  the  ordinary  first  sound 
may  be  regarded  as  composite  in  its  nature ;  being  made  up  of  the 
sound  produced  by  the  impulse  of  the  heart  against  the  parietes  of  the 
chest,  of  the  muscular  sound  occasioned  by  the  forcible  contraction  of 
the  thick  walls  of  the  ventricles,  and  of  the  sound  generated  by  the 
friction  of  the  particles  of  blood  against  each  other,  and  against  the 
boundaries  of  the  narrowing  orifices  which  lead  into  the  vessels. 

574.  The  cause  of  the  second  sound  is  simpler,  and  more  easily  un- 
derstood. It  is  due  to  the  sudden  filling-out  of  ihe  semilunar  valves 
with  blood,  at  the  moment  when  the  ventricular  systole  has  ceased,  and 
when  the  commencing  diastole  produces  a  tendency  to  the  regurgitation 
of  blood  from  the  aorta  and  pulmonary  artery.  The  sudden  passage  of 
the  valves,  from  a  state  of  complete  relaxation  to  one  of  complete  ten- 
sion, occasions  a  sort  of  click  ;  which  is  the  second  sound  of  the  heart. 
That  this  is  the  real  cause,  has  now  been  fully  demonstrated.  If  one 
of  the  valves  be  hooked  back  against  the  side  of  the  artery,  by  the  in- 
troduction of  a  curved  needle,  so  that  a  reflux  of  blood  is  permitted,  the 
sound  is  entirely  suppressed.  And  if  the  complete  closure  of  the  valves 
be  prevented  by  disease,  so  that  their  tension  is  diminished,  and  a  cer- 
tain amount  of  regurgitation  takes  place,  the  second  sound  is  no  longer 
'  eard  in  its  proper  intensity ;  whilst,  on  the  other  hand,  a  sound  analo- 


324  CIRCULATION  OF   NUTKITIVE  FLUID. 

gous  to  the  first,  and  sometimes  prolonged  over  the  whole  interval  of 
repose,  indicates  the  reflux  of  the  blood  into  the  ventricles.  When  the 
semilunar  valves  are  thickened  by  a  morbid  deposit,  their  surface  rough- 
ened, and  their  opening  narrowed,  the  'first  sound  becomes  harsher  and 
sharper ;  and  the  second  sound  acquires  the  same  character, — the  back- 
ward as  well  as  the  forward  flow  of  the  blood  being  afi'ected  by  this 
cause. 

575.  The  natural  movements  of  the  mitral  and  tricuspid  valves, 
appear  to  be  accomplished  with  perfect  freedom  from  sound ;  for  the 
size  of  the  orifices  which  thej  guard  prevents  any  considerable  friction 
of  the  blood,  in  its  flow  from  one  cavity  to  the  other ;  and  their  closure 
when  the  ventricular  systole  begins,  does  not  take  place  with  the 
rapidity  and  suddenness  of  that  of  the  semilunar  valves.  But  when 
their  structure  is  changed  by  disease,  their  action  is  not  so  noiseless ; 
and  they  give  rise  to  various  morbid  sounds,  which  are  heard  in  addi- 
tion to  the  ordinary  sounds,  and  which  may  even  obscure  them  alto- 
gether. In  tlie^  same  manner,  the  ordinary  movements  of  the  heart  do 
not  produce  any  audible  friction-sound,  between  the  two  surfaces  of 
the  pericardium,  that  which  covers  the  heart,  and  that  which  lines  the 
pericardial  sac.  These  surfaces  are  kept  moist,  in  health,  by  the  serous 
fluid  constantly,  exhaling  from  them ;  and  they  are  extremely  smooth, 
so  that  they  glide  over  one  another  noiselessly.  But  if  they  become 
dry,  as  in  the  first  stage  of  inflammation,  a  slight  creaking  is  heard, 
accompanying  both  the  ordinary  sounds  of  the  heart,  and  somewhat 
resembling  the  rustling  of  paper.  And  if  they  are  roughened  by  the 
deposit  of  inflammatory  exudations,  this  "to  and  fro"  sound  becomes  of 
a  harsher  character. 

576.  The  walls  of  the  left  ventricle  are  considerably  thicker  than 
those  of  the  right;  and  the  contractile  power  is  greater.  This  diff"erence 
is  obviously  required,  by  the  difference  in  length  between  the  systemic 
and  the  pulmonary  vessels ;  the  amount  of  force  necessary  to  drive  the 
blood  through  the  latter,  being  far  inferior  to  that  which  is  requisite 
to  propel  it  through  the  former.  The  average  thickness  of  the  walls 
of  the  left  Ventricle  is  about  4J  lines ;  being  somewhat  greater  than 
this  at  the  middle  of  the  heart,  and  less  at  its  apex.  The  average 
thickness  of  the  walls  of  the  right  ventricle  is  not  more  than  1 J  line ; 
being  a  little  greater  than  this  at  the  base,  and  less  at  the  apex  of  the 
heart.  The  left  auricle  is  somewhat  thicker  than  the  right.  The 
capacities  of  all  the  four  cavities  are  nearly  equal ;  each  of  them,  in 
the  full-sized  heart,  holding  about  two  ounces  of  fluid.  The  Ventricles 
are,  perhaps,  a  little  larger  than  their  respective  Auricles  ;  but  there  is 
no  very  positive  diff'erence  in  capacity,  between  the  Ventricles  and 
Auricles  of  the  two  sides. 

577.  The  quantity  of  blood  which  is  propelled  at  each  Ventricular 
systole,  cannot,  therefore,  exceed  two  ounces;  and  it  is  probably  some- 
what less,  as  the  ventricles  do  not  seem  to  empty  themselves  completely 
at  each  contraction.  Now  the  whole  quantity  of  the  blood  seems  to  be 
about  one-fifth  of  the  entire  weight  of  the  body ;  so  that  it  will  amount 
to  about  28  lbs.  in  an  individual  of  140  lbs.  weight.  Allowing  75  pul- 
sations to  a  minute,  150  oz.  (or  9  lbs.  6  oz.)  of  blood  would  pass  through 


CIRCUMSTANCES   AFFECTING   RATE    OF   PULSE.  325 

each  ventricle  of  the  heart  in  that  time  ;  consequently  nearly  three 
minutes  would  be  required  for  the  passage  of  the  entire  mass  of  the 
blood  through  the  whole  circle  of  its  movement,  if  its  rate  be  entirely 
determined  by  the  impulses  it  receives  from  this  central  organ.  But  it 
appears,  from  various  experiments,  that  the  rate  of  circulation  is  much 
more  rapid  than  this.  For  if  a  solution  of  any  salt,  easily  detectible  in 
the  blood  be  injected  into  one  of  the  large  veins  near  the  heart,  it  may 
be  traced  in  the  arterial  circulation  in  from  15  to  20  seconds  after- 
wards ;  during  which  interval  it  must  have  traversed  the  whole  pul- 
monary system  of  vessels,  and  passed  through  both  sides  of  the  heart. 
And  if  the  salt  be  one,  which  acts  powerfully  on  the  heart  itself, — as  is 
the  case  with  Nitrate  of  Baryta  or  Nitrate  of  Potass, — this  action  is 
manifested  almost  at  the  same  moment  with  the  appearance  of  the  salt 
in  the  arteries  of  other  parts ;  thus  showing  that  it  has  been  conveyed 
by  the  coronary  arteries  into  the  capillaries  of  the  heart  itself.  The 
period  required  for  the  transmission  of  a  saline  substance  from  the 
veins  of  the  upper  part  of  the  body  to  those  of  the  lower, — which  can 
scarcely  be  accomplished  through  any  more  direct  channel  than  the 
current  that  returns  to  the  heart,  then  passes  through  the  lungs  back 
to  the  heart  again,  and  then  flows  through  the  systemic  arteries  and 
capillaries  to  the  veins, — is  accomplished  in  little  more  than  20  seconds, 
even  in  an  animal  so  large  as  a  Horse.  It  appears,  then,  that  even 
the  vigorous  and  constant  action  of  the  Heart  is  not  alone  sufficient 
to  maintain  the  circulation  at  its  ordinary  rate ;  and  we  are  not 
justified,  therefore,  in  excluding  those  sources  of  movement  in  the 
higher  animals,  which  evidently  exert  so  important  an  influence  in  the 
lower. 

578.  The  force  with  which  the  heart  propels  the  blood  is  such,  that 
if  a  vertical  pipe  be  inserted  into  the  Carotid  artery  of  a  horse,  the 
blood  will  sometimes  rise  in  it  to  a  height  of  10  feet.  From  com- 
parative experiments  upon  other  animals,  it  has  been  estimated  that 
the  vigorous  action  of  the  heart  in  Man  would  sustain  a  column  of 
blood  in  his  aorta  about  7 J  feet  high ;  or,  in  other  words,  that  the 
force  with  which  the  heart  ordinarily  propels  the  blood  through  the 
aorta,  is  equal  to  that  which  would  be  generated  by  the  weight  of  a 
column  of  blood  of  the  same  size,  and  7^  feet  high;  which  weight 
would  be  about  4^  lbs.  But  the  force  which  must  be  exerted  by  the 
heart  to  sustain  such  a  column,  may  be  shown,  upon  physical  principles, 
to  be  as  much  greater  than  this,  as  the  area  of  a  plane  passing 
through  the  base  and  apex  of  the  left  ventricle  is  greater  than  that 
of  the  transverse  section  of  the  aorta  ;  and  as  the  proportion  of  these 
arose  is  about  3  :  1,  the  real  force  of  the  heart  may  be  stated  at  about 

;     13  lbs. 

579.  The  number  of  contractions  of  the  heart,  in  a  given  time,  is 
1  liable  to  great  variations  within  the  limits  of  health,  from  several 
j  causes :  the  chief  of  which  are  diversities  of  Age  and  Sex,  amount 
I      of  Muscular  exertion,  the   condition  of  the   Mind,  the   state  of  the 

Digestive  system,  and  the  period  of  the  Day.  The  following  are  the 
j  points  of  greatest  importance,  in  regard  to  the  action  of  these  several 
1     influences. 

i 


326  CIRCULATION  OF  NUTRITIVE  FLUID. 

Age. — The  pulse  of  the  newly-born  infant  averages  from  130  to  140 
per  minute ;  and  this  rate  gradually  diminishes,  until,  in  adult  age,  the 
pulse  averages  from  70  to  80 ;  and  in  the  decline  of  life  from  50  to  65. 

^Qx, — The  pulse  of  the  adult  female  exceeds  that  of  the  adult  male 
in  frequency,  by  about  10  or  12  beats  in  a  minute ;  and  it  is  also  more 
liable  to  disturbance  from  other  causes. 

Muscular  Exertion. — The  eifect  of  this  in  accelerating  the  pulse  is 
well  known ;  but  as  the  amount  of  change  depends  upon  the  degree  of 
exertion,  no  general  statement  can  be  made  on  the  subject.  The  con- 
tinued influence  of  a  moderate  degree  of  muscular  exertion,  is  shown  by 
the  efi*ect  of  posture  upon  the  pulse.  Thus  the  pulse  is  on  the  average 
from  7  to  10  beats  faster  (per  minute)  in  the  standing  than  in  the  sitting 
posture  ;  and  4  or  5  beats  faster  in  the  sitting  than  in  the  recumbent 
posture.  This  amount  of  variation  is  temporarily  increased  by  the 
muscular  effort  required  for  the  change  of  posture ;  but  this  soon  sub- 
sides into  the  continued  rate,  which  the  permanent  maintenance  of  the 
new  posture  involves.  There  are  certain  states  of  the  system,  in  which 
the  heart's  action  is  increased  to  a  most  violent  degree,  by  a  simple 
change  of  posture ;  and  in  which,  therefore,  it  is  necessary  that  even 
this  slight  movement  should  be  made  with  gentleness  and  caution. 

Mental  Condition. — The  action  of  the  heart  is  peculiarly  influenced, 
as  every  one  is  aware,  by  the  excitement  of  the  emotions.  This  is  a 
fact  to  which,  however  familiar,  the  medical  practitioner  should  con- 
stantly direct  his  attention.  The  trifling  agitation  occasioned  by  the 
entrance  of  the  medical  man  will  produce,  in  many  patients,  such  an 
acceleration  of  the  pulse,  as  would  be  very  alarming,  if  its  true  cause 
were  not  known.  And  the  real  rate  of  the  pulse  cannot  be  ascertained, 
until  time  has  been  permitted  for  the  agitation  to  subside ;  which  is 
favoured,  also,  by  the  influence  of  a  gentle  manner  and  tranquillizing 
conversation.  The  operation  of  the  intellectual  powers  does  not  seem 
to  aff*ect  the  rate  of  the  heart's  movement  in  any  other  way,  than  by 
inducing  a  general  state  of  feverishness,  if  it  be  too  long  or  too  ener- 
getically kept  up. 

State  of  the  Digestive  System. — The  pulse  is  quickened  during  the 
digestion  of  a  meal ;  but  no  exact  numerical  statement  can  be  made  on 
this  subject. 

Period  of  the  Day. — The  frequency  of  the  pulse  appears  to  be  some- 
what greater  in  the  morning  than  it  is  in  the  evening ;  and  the  tem- 
porary action  of  any  of  the  preceding  causes,  more  quickly  subsides  in 
the  evening  than  in  the  morning. 

580.  The  movements  of  the  heart  have  been  supposed  to  depend 
upon  a  constant  supply  of  nervous  influence,  generated  by  the  cerebro- 
spinal system,  and  transmitted  through  the  sympathetic  nerve,  the 
branches  of  which  are  copiously  distributed  to  it.  And  this  idea 
seemed  to  derive  support  from  the  fact,  that,  when  the  brain  and 
spinal  cord  are  removed,  or  when  large  portions  of  them  are  suddenly 
destroyed,  by  crushing  or  by  the  breaking-up  of  their  substance  in  any 
other  mode,  the  movements  of  the  heart  are  arrested.  But  it  has 
been  shown  that  the  brain  and  spinal  cord  may  be  gradually  removed, 
without  any  such  consequence ;  and  the  occasional  production  of  foetuses 


EQUALIZATION   OF   FLOW  IN   THE  ARTERIES.  327 

destitute  of  those  centres,  but  possessing  a  regularly-pulsating  heart, 
is  another  proof  that  the  movements  of  this  organ  do  not  depend  upon 
a  supply  of  nervous  influence  derived  from  them.  Still  they  are 
capable  of  being  influenced  by  impressions  transmitted  through  the 
nerves.  It  has  been  ascertained  by  Valentin,  that,  after  the  heart  has 
ceased  to  beat,  its  contractions  may  be  re-excited  by  stimulating  the 
roots  of  the  Spinal  Accessory  nerve,  or  of  the  first  four  Cervical 
nerves  ;  the  influence  of  that  stimulation  being  conveyed  to  the  heart 
by  the  Sympathetic  system,  the  cardiac  portion  of  which  communicates 
with  these  nerves.  Irritation  of  the  Par  Vagum,  also,  has  a  tendency 
to  accelerate  the  heart's  action,  or  to  re-excite  it  when  it  has  ceased ; 
but  the  complete  severance  of  both  its  trunks  produces  little  disturb- 
ance in  the  regularity  of  the  movement.  The  action  of  the  heart  may 
be  also  afi*ected  more  directly  through  the  Sympathetic  system ;  thus 
it  is  excited  by  irritation  of  the  cervical  ganglia,  especially  the  first ; 
whilst  continued  pressure  upon  the  cardiac  nerve,  by  an  enlarged 
bronchial  gland,  has  appeared  to  be  the  cause  of  its  occasional  suspen- 
sion. It  is  without  doubt  through  its  nervous  connexions,  and  probably 
through  the  sympathetic  system,  that  the  heart  receives  the  influence  of 
mental  emotions. 

581.  The  movements  of  the  heart  may  be  suspended,  or  altogether 
checked,  by  sudden  and  violent  impressions  on  the  nervous  centres, 
even  though  these  do  not  occasion  any  perceptible  breach  of  substance. 
Thus  in  concussion  of  the  brain,  there  is  not  merely  insensibility,  but 
also  a  complete  suspension  of  the  circulation,  occasioned  by  a  failure  of 
the  heart's  power.  This  suspension  may  be  permanent,  so  that  ani- 
mation cannot  be  restored ;  or  it  may  be  temporary,  as  in  ordinary 
fainting.  The  well-known  influence  of  blows  upon  the  epigastrium,  in 
producing  sudden  death,  is  probably  to  be  attributed  to  a  similar  cause, 
— namely,  the  shock  thus  communicated  to  the  extensive  plexus  of  gan- 
glionic nerves,  radiating  from  the  semilunar  ganglia,  and  proceeding  to 
the  abdominal  viscera.  Violent  impressions  upon  other  nervous  expan- 
sions may  produce  a  dangerous  weakening  of  the  heart's  contractile 
power ;  this  is  the  case,  for  example,  with  extensive  burns,  which  may 
produce  faintness,  and  even  death,  especially  in  children,  by  the  depres- 
sion which  they  induce.  Many  other  causes  of  sudden  suspension  of 
the  heart's  action  might  be  enumerated ;  but  they  may  be  generally 
traced  to  a  strong  impression  upon  the  nervous  system ;  though  of  the 
mode  in  which  this  operates  we  know  nothing. 

4.  Movement  of  the  Blood  in  the  Arteries. 

582.  The  Blood,  thus  propelled  from  the  Heart  into  the  Arteries  by 
a  series  of  interrupted  jets,  would  continue  to  flow  in  the  same  manner, 
if  it  were  not  for  the  equalization  of  its  movement,  eff'ected  by  the  pro- 
perties of  the  arterial  walls.  This  influence  is  exerted  by  the  middle  or 
fibrous  coat,  which  consists  in  part  of  yellow  elastic  tissue  (§  189),  and 
in  part  of  non-striated  muscular  fibre  (§  337).  The  proportion  of  these 
two  components  varies  in  arteries  of  difi'erent  calibre;   the  muscular 


t 


328  CIRCULATION   OF  NUTRITIVE   FLUID. 

tissue  being  thicker  in  the  smaller  branches,  and  the  elastic  tissue  being 
found  in  larger  amount  in  the  main  trunks. 

583.  It  is  chiefly  to  the  simple  physical  property  of  Elasticity,  thus 
possessed  by  the  Arterial  tubes,  that  we  owe  the  equalization  of  the 
flow  of  blood ;  and  we  may  hence  understand  the  reason,  why  the  trunks 
that  are  in  nearest  connexion  with  the  heart,  should  be  those  most 
endowed  with  it.  If  a  forcing-pump  were  to  inject  water,  by  successive 
strokes,  into  a  system  of  tubes  with  perfectly  unyielding  walls,  the  flow 
of  fluid  at  the  further  extremities  of  these  tubes  would  be  as  much 
interrupted  as  its  entrance  into  them.  But  if  the  pump  be  connected 
with  an  air-vessel  (as  in  the  common  fire  engine),  so  that  a  part  of  the 
force  of  each  stroke  is  expended  in  compressing  the  air,  the  expansion 
of  this,  during  the  interval  between  the  successive  strokes,  produces  a 
continuous  flow  of  water  along  the  tubes.  Or  if  the  tubes  themselves 
were  endowed  with  a  certain  degree  of  elasticity,  which  should  allow 
them  to  dilate  near  their  commencement,  so  as  to  receive  the  new 
charge  of  flmd,  and  which  should  occasion  a  continued  pressure  upon 
the  fluid  during  the  interval  of  the  stroke,  the  same  equalizing  effect 
would  be  produced.  This  is  precisely  the  case  with  the  Arterial  system ; 
the  intermittent  jets,  by  which  the  blood  is  propelled  from  the  heart, 
are  speedily  converted  into  a  continued  stream ;  so  that,  at  even  a  mode- 
rate distance  from  the  heart,  the  only  indication  of  its  interrupted  action 
is  presented  by  the  greater  or  less  rapidity  of  the  flow ;  and  this  gives 
rise,  when  an  artery  is  divided,  to  an  alternate  rise  and  fall  of  the  jet 
of  blood,  and,  in  the  ordinary  circulation,  to »the  phenomenon  called  the 
pulse.  This  is  due  to  an  increase  in  the  dimension  of  the  arterial  tube, 
both  in  length  and  breadth,  with  each  additional  ingress  of  blood ;  the 
increase  in  length  is  the  more  considerable  of  the  two  effects,  and  causes 
the  artery  to  be  somewhat  lifted  from  its  seat.  During  the  intervals,  a 
quantity  of  blood  corresponding  to  that  which  had  entered,  escapes 
by  the  further  extremity  of  the  tube;  and  thus  the  artery  is  enabled 
to  contract  to  its  previous  dimensions,  and  to  return  to  its  bed.  We 
may  compare  the  pulse,  therefore,  to  a  wave,  which  commences  in  the 
heart,  and  travels  onwards  through  the  arterial  system. 

584.  In  the  large  arteries  near  the  heart,  the  pulsation  is  always 
precisely  synchronous  with  the  ventricular  systole ;  but  it  takes  place 
somewhat  later  in  the  arteries  at  a  distance  from  the  heart ;  the  time 
required  for  the  transmission  of  the  wave  being  proportioned  to  the 
degree  in  which  the  walls  of  the  arteries  yield  to  it.  If  they  were  quite 
rigid,  the  egress  at  one  extremity  must  take  place  at  the  precise  moment, 
that  the  fluid  is  forced  into  the  other.  On  the  other  hand,  if  the  walls 
be  too  easily  distensible,  they  yield  to  the  propelling  force  in  such  a 
degree  that  it  is  entirely  expended  upon  them ;  and  the  fluid  is  not 
moved  onward  at  all  or  but  very  slowly.  In  the  healthy  state  of  the 
arterial  walls,  they  should  contract  upon  their  contents  with  sufficient 
force  to  equalize  the  flow  of  blood,  and  to  prevent  the  pulse-wave  from 
occupying  more  than  one-sixth  or  one-seventh  of  a  second,  in  its  propa- 
gation to  the  remotest  arteries  of  the  system ;  and  the  pulse  should  be 
full,  producing  a  prolonged  but  gentle  elevation  beneath  the  finger,  and 
capable  of  resisting  moderate  pressure.     This  condition  is  dependent 


EFFECTS  OF  MUSCULARITY  OF  ARTERIES.  329 

in  great  part  upon  the  due  tonicity  of  the  muscular  coat  of  the  arteries 
(§  365).  When  this  tonicity  is  in  excess,  the  walls  of  the  arteries  are 
too  rigid ;  the  pulse  at  the  wrist  is  felt  to  occur  exactly  at  the  same 
time  with  the  ventricular  systole;  and  its  character  is  that  of  strength, 
incompressibility,  and  sustained  power,  though  it  may  he  even  slower 
than  usual.  This  is  the  Case  in  what  is  commonly  termed  "high  condi- 
tion" of  the  system;  which  predisposes  to  inflammatory  disorders,  but 
which  renders  it  less  susceptible  than  usual  to  the  influence  of  mala- 
ria, contagious  miasmata,  or  other  causes  of  a  depressing  character. 
On  the  other  hand,  when  the  tonicity  of  the  arteries  is  less  than  it 
should  be,  their  walls  yield  too  much  to  the  pulse-wave ;  so  that  the 
pulse  at  the  wrist  is  often  felt  even  after  the  second  sound  is  heard ;  and 
the  pulse  itself  is  jerking,  unsteady,  and  too  easily  compressible.  This 
loose  relaxed  state  of  the  vessels  is  the  most  unfavourable  that  can  be 
to  regularity  and  vigour  of  the  circulation;  and  it  manifests  its  ill 
eff"ects  in  the  general  condition  of  the  system,  which  is  then  peculiarly 
prone  to  suffer  from  the  agency  of  malaria,  infectious  miasmata,  or 
any  other  depressing  causes. 

585.  Although  many  Physiologists  have  denied  that  the  Arteries 
possess  real  Muscular  Contractility  in  any  degree,  yet  there  can  be  no 
longer  any  doubt  on  the  subject ;  since  numerous  experimenters  have 
succeeded  in  producing  distinct  contraction  in  their  walls,  by  the  appli- 
cation of  those  stimuli  which  act  upon  muscular  fibre  in  general.  More- 
over it  has  been  ascertained,  that  when  an  artery  is  dilated  by  the  blood 
injected  into  it  from  the  heart,  it  reacts  with  a  force  superior  to  the 
impulse  to  which  it  yielded  ;  and  that,  if  a  portion  of  an  artery  from  an 
animal  recently  dead,  in  which  the  vital  properties  are  still  preserved, 
and  a  similar  portion  from  an  animal  that  has  been  dead  some  days,  in 
which  nothing  but  the  elasticity  remains,  be  distended  with  equal  force, 
the  former  contracts  to  a  much  greater  degree  than  the  latter  after  the 
distending  force  is  withdrawn. — One  use  of  this  contractile  power  may 
very  probably  be,  to  assist  the  Heart  in  maintaining  the  flow  of  blood ; 
for  if  the  arterial  walls  yield  readily  to  the  ingress  of  blood,  and  then 
contract  upon  their  contents  with  a  force  greater  than  that  which  dis- 
tended them,  the  current  must  necessarily  be  propelled  onwards  with 
greater  force.  This  supplementary  propelling  force,  on  the  part  of  the 
arteries,  may  serve  as  a  compensation  to  that  diminution  of  the  heart's 
power,  which  must  result  from  the  increased  friction  of  the  blood  against 
the  walls  of  the  vessels  occasioned  by  their  subdivision ;  and  we  thus 
observe,  even  in  the  highest  animals,  some  traces  of  that  diff'used  agency, 
on  which  the  Circulation  is  so  much  more  dependent  in  th^  lower  tribes. 

586.  It  seems  probable,  however,  that  one  chief  use  of  the  Muscu- 
larity of  the  Arterial  walls,  consists  in  its  regulation  of  the  diameter 
of  the  tubes,  in  accordance  with  the  quantity  of  blood  to  be  conducted 
through  them  to  any  part ;  the  proper  amount  being  determined  by 
circumstances  at  the  time.  Such  local  changes  may  form  a  part  of  the 
regular  series  of  actions  of  the  human  body,  as  when  the  Uterine  and 
Mammary  arteries  undergo  enlargement,  at  the  periods  of  pregnancy 
and  parturition  ;  and  they  occur  still  more  frequently  in  diseases,  which 
are  attended  by  increased  action  of  particular  organs.     In  such  cases, 


330  CIRCULATION   OF   NUTRITIVE   FLUID. 

it  cannot  be  vis  a  tergo  of  the  Heart,  that  occasions  the  enlargement  of 
certain  arterial  trunks,  and  of  no  others ;  since  any  increase  in  its  pro- 
pulsive power  would  affect  all  alike.  It  must  be,  therefore,  through 
a  power  inherent  in  themselves,  that  the  dilatation  takes  place ;  and 
there  seems  much  reason  for  attributing  to  the  Sympathetic  system  of 
nerves  a  control  over  this  power,  and  consequently  the  oflSce  of  regu- 
lating the  local  distribution  of  blood,  in  accordance  with  the  wants  of 
the  different  parts.  It  is  well  known  that  the  nerves  of  this  system  are 
copiously  distributed  upon  the  arterial  walls ;  and  it  has  been  experi- 
mentally shown,  that  they  have  the  power  of  producing  contractions  in 
the  larger  arteries.  Moreover,  there  is  every  reason  to  believe  that 
the  diameter  of  the  Capillary  blood-vessels,  and  the  rate  of  the  move- 
ment of  the  blood  through  them  is  much  influenced  by  these  nerves 
(§  603) ;  and  it  seems  highly  probable,  therefore,  that  they  should  have 
a  corresponding  influence  upon  the  size  of  the  trunks,  from  which  these 
capillaries  are  derived. 

587.  The  Arterial  system  possesses  nearly  the  same  relative  capacity 
in  every  part ;  that  is,  if  a  section  could  be  made  through  all  the  sys- 
temic arteries  at  a  certain  distance  from  the  heart,  the  united  areas 
would  be  found  equal  to  that  of  the  aorta ;  and  those  of  the  branches 
of  the  pulmonary  arteries  would  equal  those  of  their  trunk.  This  re- 
sults from  the  fact,  that,  at  every  subdivision,  the  united  areas  of  the 
branches  are  almost  precisely  equal  to  that  of  the  trunks  from  which 
they  proceed ;  although  the  united  diameters  of  the  former  far  exceed 
that  of  the  latter.  According  to  a  well-known  mathematical  law,  the 
areas  of  circles  are  as  the  squares  of  the  diameters ;  consequently,  in 
making  such  comparisons,  it  is  necessary  to  square  the  diameters  of  the 
trunk  and  those  of  the  branches,  and  to  contrast  the  former  with  the 
sum  of  the  latter.  Thus  a  trunk  whose  diameter  is  7,  may  subdivide 
into  two  branches,  each  having  a  diameter  of  nearly  5 ;  for  the  square 
of  7  is  49,  and  twice  the  square  of  5  is  50.  Or  a  trunk  whose  diameter 
is  17  may  subdivide  into  three  branches  whose  diameters  are  10,  10, 
and  9 J  (making  29|  as  the  sum  of  the  diameters) ;  for  the  square  of  the 
diameter  of  the  trunk  is  289,  whilst  the  sum  of  the  squares  of  those  of 
the  branches  is  290J.  It  appears,  however,  from  Mr.  Paget's  recent 
admeasurements,  that  there  is  seldom  an  exact  equality  between  the 
area  of  the  trunk  and  that  of  its  branches ;  the  area  sometimes  increas- 
ing, and  sometimes  diminishing.  The  former  seems  the  general  rule 
in  the  upper  extremities  ;  the  latter  in  the  lower.  Thus  the  area  of  the 
trunk  of  the  external  carotid  is  to  that  of  its  branches,  as  100  to  119 ; 
whilst  the  area  of  the  abdominal  aorta,  just  before  its  final  division, 
is  to  that  of  its  branches  as  100  to  89. 

588.  In  almost  every  part  of  their  course,  the  ramifications  of  the 
arteries  communicate  freely  with  each  other,  by  anastomosis  ;  and  this 
communication  is  most  important,  as  affording  the  means  by  which  the 
circulation  is  sustained,  when  the  current  through  the  main  trunk  is  ob- 
structed. There  is  scarcely  an  artery  in  the  body,  except  the  aorta, 
which  may  not  be  tied,  with  the  certainty  that  the  blood  will  still  be 
conducted  to  its  destination,  by  the  collateral  circulation.  At  first, 
the  quantity  which  thus  passes  is  very  insignificant,  and  is  by  no  means 


ARRANGEMENT  OF   CAPILLARY  VESSELS.  331 

sufficient  to  supply  what  is  needed ;  thus,  when  the  femoral  artery  has 
been  tied  for  popliteal  aneurism,  the  limb  becomes  cold,  and  the  sensi- 
bility of  the  surface  and  its  muscular  power  are  alike  diminished.  In  a 
few  hours,  however,  its  warmth  returns,  and  its  sensibility  and  muscular 
power  are  restored ;  indicating  that  its  circulation  has  been  already  re- 
established through  the  collateral  branches.  And  where  an  opportunity 
presents  itself  at  a  subsequent  period  for  examining  the  state  of  the 
vessels  in  such  a  limb,  it  is  found  that  an  extraordinary  enlargement 
has  taken  place  in  arteries  that  were  previously  of  insignificant  size, 
which  form  a  communication  between  the  branches  that  issue  above  and 
below  the  interruption.  Moreover,  it  is  commonly  found  that  the  main 
trunk  has  become  completely  impervious  above  the  part  where  it  was 
obliterated  by  the  ligature,  up  to  the  point  at  which  the  nearest  lateral 
branch  is  given  off. — Even  the  abdominal  aorta  has  been  tied  in  dogs, 
without  fatal  results ;  the  circulation  in  the  posterior  part  of  the  body, 
and  in  the  hinder  extremities,  being  then  maintained  chiefly  by  the 
inosculation  of  the  external  mammary  artery  with  the  epigastric,  upon 
the  parietes  of  the  abdomen. 

5.  Movement  of  Blood  in  the  Capillaries. 

589.  The  ultimate  ramifications  of  the  Arteries  pass  so  insensibly 
into  those  of  the  Veins,  that  no  definite  line  of  demarcation  between 
them  can  be  drawn ;  and  although  we  are  in  the  habit  of  speaking  of 
the  "Capillaries"  as  a  distinct  system  of  vessels,  yet  it  ought  to  be 
strictly  borne  in  mind,  that  they  difier  only  in  size  from  the  vessels 
from  which  they  receive  their  blood  on  the  one  side,  and  into  which 
they  pour  it  on  the  other.  It  was  at  one  time  supposed,  that  they  were 
merely  channels  or  passages,  excavated  in  the  tissues,  having  no  definite 
walls  of  their  own.  This  is  probably  true  of  them  in  the  lower  tribes 
of  Animals ;  and  it  may  also  be  the  case  at  an  early  stage  of  their 
development  in  the  higher.  But  when  their  formation  is  complete, 
they  undoubtedly  possess  walls  of  a  fibrous  texture,  as  distinct  as  those 
of  the  arteries  and  veins,  though  of  extreme  thinness.  From  the  occa- 
sional appearance  of  bodies  resembling  cell-nuclei,  in  the  substance  of 
the  walls  of  the  capillaries,  it  has  been  thought  that  their  tubes  are 
formed,  in  the  first  instance,  by  the  coalescence  of  cells  arranged  in  a 
linear  direction ;  and  this  idea  receives  confirmation  from  the  fact,  that 
the  ducts  of  Plants  are  undoubtedly  formed  in  this  manner,  and  not  by 
the  mere  retirement  of  the  tissues  on  either  side,  leaving  an  intervening 
channel.  The  closely-reticulated  structure  usually  formed  by  the  capil- 
laries, has  been  commonly  regarded  as  distinguishing  them  both  from 
the  arteries  and  the  veins ;  and  it  is  not  unusual  to  speak  of  the  arteries 
as  delivering  the  blood  into  the  "capillary  network,"  and  of  the  veins 
as  receiving  the  fluid  that  has  traversed  this.  Such  expressions  are 
not  incorrect  as  implying  the  simple  fact,  that  between  the  arteries  and 
the  veins  is  a  network  of  minute  vessels,  through  which  the  blood  has 
to  travel  when  proceeding  from  one  to  the  other ;  but  these  vessels 
must  not  be  regarded  as  belonging  to  a  distinct  class,  being  nothing 


332 


CIRCULATION   OF   NUTRITIVE  FLUID. 


else  than  the  minutest  subdivisions  of  the  veins  and  arteries,  which 
commonly  inosculate  freely  with  each  other. 

590.  The  degree  of  this  inosculation,  and  the  consequent  form  of  the 
capillary  network,  are  subject,  however,  to  very  great  variations ;  and 
these  may  be  generally  shown  to  have  a  relation  to  the  form  of  the 
ultimate  elements  of  the  tissues,  which  are  traversed  by  the  capillaries. 
Thus  we  have  seen  in  the  capillaries  of  Muscle,  that  the  major  part  run 
parallel  to  the  course  of  the  fibres,  lying  in  the  minute  interspaces  be- 
tween them  (Fig.  67);  a  few  transverse  branches  serving  to  connect 
them  with  each  other.  A  similar  distribution  prevails  in  the  capillaries 
of  the  Nervous  trunks ;  but  those  of  the  Nervous  centres  are  arranged 
in  the  form  of  a  minute  network,  so  as  completely  to  traverse  every 
part  of  the  structure  (Fig.  93).  Again,  we  observe  that  the  capillaries 
of  Glands  form  a  minute  network  around  the  secreting  follicle  (Fig. 
94);  and  a  similar  arrangement  prevails  in  the  capillaries  of  the  air- 
cells  of  the  lungs,  which  are  set  so  closely  together,  that  it  would  seem 


Fig.  93. 


Fig.  94. 


Capillary  Network  of  Nervous  Centres. 


Capillary  Network  around  the  follicles  of 
Parotid  Gland. 


as  if  the  purpose  were  to  cover  the  surface  with  blood  as  completely  as 
possible,  consistently  with  its  being  retained  within  vessels,  and  not 
spread  out  into  a  continuous  film  (Fig.  106).  A  network  of  very  much 
the  same  character  is  found  in  the  villi  of  the  mucous  membrane  (Fig. 


Fig.  95. 


Fig.  96. 


Capillary  Network  in  simple  mucous  mem- 
brane of  palpebral  conjunctiya. 


Capillary  Network  in  choroid  coat  of 
the  eye. 


82),  on  the  ordinary  surface  of  simple  mucous  membrane  (Fig.  95),  and 
on  that  of  the  choroid  coat  of  the  eye  (Fig.  96).  Where  the  surface  of 
the  mucous  membrane  is  depressed  into  follicles,  the  arrangement  of  the 


DISTRIBUTION   OF   THE   CAPILLARIES. 


833 


capillaries  has  an  evident  reference  to  these  (Fig.  97) ;  whilst,  on  the 
other  hand,  where  the  surface  of  the  skin  is  raised  up  into  sensory 
papillae,  the  capillary  network  sends  looped  prolongations  into  them, 
which  are  found  accompanying  their  nerves  (Figs.  98  and  99). 

591.  It  cannot  be  supposed  that  the  arrangement  of  the  vessels  has 
any  further  influence  upon  the  function  of  the  part  they  traverse,  than 


Distribution  of  Capillaries  around  follicles 
of  Mucous  Membrane. 


Distribution  of  Capillaries  at  the  surface  of 
the  skin  of  the  finger. 


that  which  it  derives  from  the  regulation  of  the  supply  of  blood  afforded 
to  each  individual  portion  of  the  structure.     The  form  of  the  capillary 

Fig.  99. 


Capillary  Network  of  fungiform  papilla  of  the  tongue. 

network  is  evidently  determined  by  that  of  the  elements  of  the  tissues 
permeated  by  it ;  these  are  the  real  operative  instruments  in  every  part ; 
and  the  distribution  of  the  blood-vessels  is  so  arranged,  as  to  afford 
them  precisely  the  amount  of  nourishment  they  respectively  require. 
Thus  w^e  have  seen,  that  there  are  many  living  parts,  possessing  most 
important  functions,  in  the  human  body,  which  are  not  in  any  direct 
relation  with  blood-vessels,  and  which  yet  derive  their  whole  nutriment, 
and  the  materials  of  their  functional  operation^,  from  the  blood.  This 
is  the  case,  for  example,  with  the  whole  of  the  epithelial  and  epidermic 
cells ;  and  also  with  the  articular  cartilages,  and  the  substance  of  the. 
teeth.  Even  in  bone,  the  islets  between  the  Haversian  canals,  which 
are  completely  unpenetrated  by  vessels,  are  of  considerable  size.  Such 
islets  must  everywhere  exist,  between  the  meshes  of  the  capillary  net- 
work ;  so  that  the  question  of  the  vascularity  or  non-vascularity  of  a 
tissue  is  one  of  degree  only ; — the  ultimate  fibre  of  muscle  or  nerve, 
and  the  cells  and  fibres  of  other  tissues,  being  as  completely  non- vascular, 
as  the  entire  substance  of  a  tooth  or  of  an  articular  cartilage ;  the  latter 
being  nourished,  like  the  former,  by  imbibition  from  the  surrounding 
vessels. 

592.  The  term  "Capillary"  may  be  employed  in  an  extended  or  a 


334  CIRCULATION   OF  NUTRITIVE   FLUID. 

restricted  sense ;  in  the  former  it  includes  all  the  minute  vessels  which 
pass  between  the  arteries  and  the  veins ;  in  the  latter  it  is  applied  only 
to  those  which  admit  no  more  than  a  single  file  of  blood-discs  at  once, 
and  excludes  those  which  admit  two,  three,  or  even  four  rows,  even 
although  they  establish  a  direct  communication  from  one  side  of  the 
network  to-  the  other.  The  former  application  of  the  term  is  the  most 
convenient,  although  perhaps  not  the  most  strictly  accurate ;  and  it  will 
be  therefore  here  employed  in  its  extended  sense.  And  this  is  rendered 
more  correct  by  the  fact,  that  the  size  of  the  individual  capillaries  is 
by  no  means  permanent ;  an  enlargement  often  taking  place  in  one,  and 
a  contraction  in  another,  at  the  same  time :  so  that  vessels,  which  were 
previously  true  capillaries,  no  longer  remain  such ;  and  passages,  which 
were  previously  of  far  greater  calibre,  are  reduced  to  the  average 
diameter. 

593.  The  opinion  was  long  entertained,  that  there  are  vessels  adapted 
to  the  supply  of  the  white  or  colourless  tissues ;  carrying  from  the 
arteries  only  the  fluid  portion  of  the  blood,  or  liquor  sanguinis,  and 
leaving  the  rest  behind.  No  other  such  vessels  have  been  really  ob- 
served, however,  than  the  capillaries  in  a  state  of  unusual  contraction, 
as  just  now  mentioned.  And  it  may  be  safely  affirmed,  that  the  suppo- 
sition of  their  existence  is  not  required.  For  any  one  who  observes 
the  smallest  capillary  vessels  under  the  microscope,  may  perceive,  that 
the  current  of  blood  which  passes  through  them  is  almost  free  from 
colour, — as  the  red  corpuscles  themselves  appear  to  be,  when  spread 
out  in  a  single  layer.  Tissues  which  are  rather  scantily  permeated  by 
such  vessels,  therefore,  may  still  be  white ;  and  it  is  only  where  the 
network  is  very  close,  and  the  quantity  of  blood  which  passes  through 
it  is  consequently  great,  that  a  perceptible  colour  will  be  communicated 
by  the  red  corpuscles.  And  we  have  seen,  that  the  idea  that  Nutrition 
can  only  be  carried  on  by  direct  communication  with  vessels,  is  entirely 
unfounded ;  the  .tissues  into  which  no  blood-vessels  can  be  traced,  being 
adapted  to  nourish  themselves,  like  cellular  Plants,  by  the  imbibition  of 
fluid  at  their  surfaces,  on  which  vessels  are  (for  the  most  part)  copiously 
distributed. 

594.  That  the  blood  can  only  minister  to  the  operations  of  Nutrition, 
Secretion,  &c.,  whilst  it  is  circulating  through  the  Capillaries,  is  evident 
from  several  considerations.  The  thickness  of  the  walls  of  the  larger 
vessels  interposes  an  eff'ectual  barrier  to  its  transudation ;  and  so  com- 
pletely is  the  blood  cut  off"  even  from  penetrating  these,  that  they  do 
not  derive  their  own  nourishment  from  the  blood  which  flows  through 
their  tubes,  but  from  a  capillary  network  in  their  own  substance,  which 
is  supplied  by  vessels  from  collateral  branches, — these  being  termed  the 
vasa  vasorum.  Moreover  it  is  by  the  inosculation  of  the  capillaries 
alone,  that  the  minute  network  is  formed,  which  serves  to  bring  the 
blood  into  proximity  with  the  minute  parts  of  the  tissues  to  be  nourished; 
thus  let  it  be  supposed  that  the  minute  arteries  of  Muscle  were  to  ter- 
minate in  veins,  without  undergoing  further  subdivision,  the  islets  left 
between  their  anastomosing  branches  would  be  far  too  large,  and  the 
nutritive  materials  would  consequently  not  be  supplied  with  sufficient 
readiness,  even  supposing  that  it  could  freely  permeate  the  walls  of 


VARYING   SIZE   OF  THE   CAPILLARIES.  335 

these  vessels. — The  capillaries,  then,  must  not  be  regarded  as  altogether 
distinct  in  their  endowments,  from  the  vessels  with  which  they  are  con- 
nected on  either  side ;  but  merely  as  intended,  by  their  minute  sub- 
division and  inosculation,  to  bring  the  blood  into  sufficiently  close  rela- 
tion with  the  tissues  they  are  to  nourish,  and  to  allow  a  greater  degree 
of  transudation  of  its  elements  by  the  comparative  thinness  of  their 
walls. 

595.  When  the  flow  of  blood  through  the  Capillaries  of  a  trans- 
parent part,  such  as  the  web  of  a  Frog's  foot,  is  observed  with  the 
microscope,  it  appears  at  first  to  take  place  with  great  evenness  and 
regularity.  The  influence  of  the  contractions  of  the  heart  may  be  seen 
to  extend  itself  into  the  smaller  arteries ;  the  blood  moving  onwards 
in  them  with  a  somewhat  jerking  motion.  But  this  influence  alto- 
gether disappears  in  the  capillary  network ;  the  flow  of  blood  through 
this  being  even  and  continuous,  except  when  the  action  of  the  heart  is 
becoming  weak  and  irregular,  or  when  its  influence  is  impeded  by 
obstruction  in  the  vessels  leading  to  the  part, — the  blood  being  then 
impelled  by  a  succession  of  jerks,  with  intervals  of  complete  repose. 
But  on  watching  the  movement  for  some  time,  various  changes  may 
be  observed,  which  cannot  be  attributed  to  the  heart's  influence,  and 
which  show  that  a  certain  regulating  or  distributive  power  exists  in 
the  walls  of  the  capillaries,  or  in  the  tissues  which  they  traverse.  Not 
only  do  we  occasionally  perceive  some  of  the  tubes  enlarging,  so  as  to 
admit  several  files  of  blood-discs  instead  of  one,  whilst  others  that 
previously  received  several  now  only  admit  one ;  —  but  we  also  see 
vessels  coming  into  view,  which  were  not  previously  noticed,  whilst 
other  vessels  seem  to  become  obliterated.  This  apparently  new  forma- 
tion and  obliteration  of  vessels,  however,  does  not  really  take  place ; 
for  a  more  close  examination  shows,  that  the  former  of  these  appear- 
ances is  due  to  the  entrance  of  red  corpuscles  into  passages  which 
existed  before,  but  which  were  in  such  a  state  of  contraction  as  enabled 
them  only  to  admit  the  fluid  portion  of  the  blood ;  whilst,  by  a  con- 
verse change  in  certain  capillaries,  from  the  dilated  to  the  contracted 
state,  the  appearance  of  obliteration  is  produced,  the  red  corpuscles 
being  excluded,  and  the  transparent  fluid  of  the  blood  being  alone 
transmitted  by  them. 

596.  But  these  are  by  no  means  all  the  irregularities  which  may 
be  detected  by  a  close  scrutiny  of  the  Capill/iry  circulation.  The 
velocity  of  the  current  is  liable  to  great  and  sudden  variations,  which 
cannot  be  accounted  for  by  any  change  in  the  heart's  action,  or  in  the 
supply  of  blood  afi'orded  by  the  arteries ;  and  this  change  may  manifest 
itself,  either  in  the  whole  capillary  network  of  a  part,  or  in  a  portion 
of  it;  the  circulation  taking  place  with  diminished  rapidity  in  one 
part,  and  with  increased  energy  in  another,  though  both  are  supplied 
by  the  same  trunk.  These  variations  are  sometimes  manifested  by  the 
complete  change  in  the  direction  of  the  movement,  in  certain  of  the 
transverse  or  communicating  branches ;  this  movement  taking  place,  of 
course,  from  the  stronger  towards  the  weaker  current.  Not  unfrequently 
an  entire  stagnation,  of  longer  or  shorter  duration,  precedes  the 
reversal  of  the  direction.     Irregularities  of  this  kind  are  most  frequent 


336  CIRCULATION   OF  NUTRITIVE  FLUID. 

when  the  heart's  action  is  enfeebled  or  partially  interrupted ;  and  it 
would  thus  appear,  that  the  local  influences  by  which  they  are  produced, 
are  overcome  by  the  propelling  power  of  the  central  organ,  when  this 
is  acting  with  its  full  vigour.  When  the  whole  current  has  nearly  stag- 
nated, and  a  fresh  impulse  from  the  heart  renews  it,  the  movement  is 
seldom  uniform  through  the  entire  plexus  supplied  by  one  trunk ;  but  is 
much  greater  in  some  of  the  tubes  than  in  others, — the  variation  being 
in  no  degree  connected  with  their  size,  and  being  very  different  in  its 
amount  at  short  intervals. 

597.  All  these  circumstances  indicate  that  the  movement  of  blood 
through  the  Capillaries  is  very  much  influenced  by  local  forces;  although 
these  forces  are  not  sufficiently  powerful,  in  the  higher  animals,  to 
7naintain  it  alone.  And  from  other  facts  it  appears,  that  the  condi- 
tions necessary  for  the  energetic  flow  of  blood  through  these  vessels, 
are  nothing  else  than  the  active  performance  of  the  nutritive  and  other 
operations,  to  which  they  are  subservient.  The  examination  of  a  single 
one  of  these  processes,  will  afford  us  the  requisite  proof.  The  blood 
when  circulating  through  the  systemic  capillaries,  yields  a  portion  of  its 
oxygen  to  the  tissues  it  permeates,  and  receives  from  them  carbonic 
acid.  On  the  other  hand,  when  passing  through  the  pulmonary  capil- 
laries, it  gives  up  its  carbonic  acid  to  the  atmosphere,  and  imbibes  a 
fresh  supply  of  oxygen.  Now  if  either  of  these  changes  be  prevented 
from  taking  place,  a  retardation  and  even  a  complete  stagnation  of  the 
blood  will  take  place, — the  flow  through  the  capillaries  being  now 
resisted,  instead  of  accelerated,  by  the  relation  which  the  blood  bears  to 
the  tissues.  Thus  it  has  been  shown,  that  if  an  animal  be  partially 
deprived  of  oxygen,  so  that  the  arterial  blood  is  not  duly  aerated  (rather 
resembling  the  ordinary  venous  blood),  and  cannot  exert  its  proper 
action  on  the  tissues,  the  pressure  upon  the  walls  of  the  systemic 
arteries  is  increased^  although  the  supply  of  blood  propelled  by  the 
heart,  and  the  propulsive  power  of  the  heart  itself  are  diminished;  and 
this  plainly  indicates  a  retardation  in  the  systemic  capillaries,  producing 
an  undue  accumulation  in  the  arteries.  On  the  other  hand,  the  sus- 
pension of  the  supply  of  oxygen  to  the  lungs,  either  by  an  obstruction 
in  the  air  passages,  or  by  the  substitution  of  some  other  gas,  brings  the 
pulmonary  circulation  to  a  stand  in  a  very  short  time,  the  blood  not 
being  able  to  undergo  its  usual  changes  in  the  capillaries  of  those  organs; 
and  by  this  stagnation,  the  whole  movement  of  blood  is  speedily  checked. 
The  readmission  of  oxygen,  if  the  suspension  of  the  circulation  have 
not  been  too  long  continued,  occasions  the  renewal  of  the  movement  in 
the  capillaries,  and  thence  in  the  whole  circle  of  vessels ;  and  this  even 
after  the  heart  has  ceased  to  propel  blood  towards  the  lungs. 

598.  The  principles  already  noticed  (§  547),  as  put  forth  by  Prof. 
Draper,  seem  fully  adequate  to  explain  these  phenomena.  The  arterial 
blood, — containing  oxygen  with  which  it  is  ready  to  part,  and  being 
prepared  to  receive  in  exchange  the  carbonic  acid  which  the  tissues  set 
free, — ^must  obviously  have  a  greater  affinity  for  the  tissues,  than  venous 
blood,  in  which  both  these  changes  have  been  already  effected.  Conse- 
quently, upon  mere  physical  principles,  the  arterial  blood,  which  enters 
the  systemic  capillaries  on  one  side,  must  drive  before  it,  and  expel  on 


MOVEMENT   OF   BLOOD   IN   CAPILLARIES.  337 

the  other  side  of  the  network,  the  blood  which  has  become  venous 
whilst  traversing  it.  But  if  the  blood  which  enters  the  capillaries  have 
no  such  affinity,  no  such  motor  powjer  can  bfe  developed.  On  the  other 
hand,  in  the  capillaries  of  the  lungs,  the  opposite  affinities  prevail.  The 
venous  blood  and  the  air  in  the  pulmonary  cells  have  a  mutual  attrac- 
tion, which  is  satisfied  by  the  exchange  of  oxygen  and  carbonic  acid 
that  takes  place  through  the  walls  of  the  capillaries ;  and  when  the 
blood  has  become  arterialized,  it  no  longer  has  any  attraction  for  the 
air.  Upon  the  very  same  principle,  therefore,  the  venous  blood  will 
drive  the  arterial  before  it,  in  the  pulmonary  capillaries,  whilst  respira- 
tion is  properly  going  on ;  but  if  the  supply  of  oxygen  be  interrupted, 
so  that  the  blood  is  no  longer  aerated,  no  change  in  the  affinities  takes 
place  whilst  it  traverses  the  capillary  network  ;  the  blood,  continuing 
venous,  still  retains  its  need  of  a  change  and  its  attraction  for  the  walls 
of  the  capillaries;  and  its  egress  into  the  pulmonary  veins  is  thus 
resisted,  rather  than  aided,  by  the  force  generated  in  the  lungs. 

699.  The  change  in  the  condition  of  the  blood,  in  regard  to  the 
relative  proportions  of  its  oxygen  and  carbonic  acid,  is  the  only  one  to 
which  the  Pulmonary  circulation  is  subservient ;  but  in  the  Systemic 
circulation,  the  changes  are  of  a  much  more  complex  nature, — every 
distinct  organ  attracting  to  itself  the  peculiar  substances  which  it 
requires  as  the  materials  of  its  own  nutrition,  and  the  nature  of  the 
affinities  thus  generated  being  consequently  different  in  each  case.  But 
the  same  law  holds  good  in  all  instances.  Thus  the  blood  conveyed  to 
the  liver  by  the  portal  vein,  contains  the  materials  at  the  expense  of 
which  the  bile-secreting  cells  are  developed ;  consequently  the  tissue  of 
the  liver  which  is  principally  made  up  of  these  cells,  possesses  a  certain 
degree  of  affinity  or  attraction  for  blood  containing  these  materials ;  and 
this  is  diminished,  so  soon  as  they  have  been  drawn  from  it  into  the  cells 
around.  Consequently  the  blood  of  the  portal  vein  will  drive  before  it, 
into  the  hepatic  vein,  the  blood  which  has  traversed  the  capillaries  of 
the  portal  system,  and  which  has  given  up,  in  doing  so,  the  elements  of 
bile  to  the  solid  tissues  of  the  liver.  The  same  principle  holds  good  in 
every  other  case. 

600.  We  are  now  prepared,  therefore,  to  understand  the  general 
principle,  that  the  rapidity  of  the  circulation  of  a  part  will  depend  in 
great  measure  upon  the  activity  of  the  fuilctional  changes  taking  place 
in  it, — the  heart's  action,  and  the  state  of  tho  general  circulation, 
remaining  the  same.  When,  by  the  heightened  vitality,  or  the  unusual 
exercise,  of  a  part,  the  changes  which  the  blood  naturally  undergoes  in 
it  are  increased  in  amount,  the  affinities  which  draw  the  arterial  blood 
into  the  capillaries  are  stronger,  and  more  speedily  satisfied,  and  the 
venous  blood  is  therefore  driven  out  with  increased  energy.  Thus  a 
larger  quantity  of  blood  will  pass  through  the  capillaries  of  the  part  in 
a  given  time,  without  any  enlargement  of  their  calibre,  and  even  though 
it  be  somewhat  diminished ;  but  the  size  of  the  arteries  by  which  it  is 
supplied  soon  undergoes  an  increase,  which  adapts  it  to  supply  the 
increased  demand.  Any  circumstance,  then,  which  increases  the  func- 
tional energy  of  a  part,  or  stimulates  it  to  increased  nutrition,^  will 
occasion  an  increase  in  the  supply  of  blood,  altogether  irrespectively 

22 


338  CIRCULATION  OF  NUTRITIVE   FLUID. 

of  any  change  in  the  heart's  action.  This  principle  has  long  heen 
known,  and  has  been  expressed  in  the  concise  adage,  "Ubi  stimulus, 
ibi  fluxus;"  which  those  Physiologists  who  maintain  that  the  Circu- 
lation is  maintained  and  governed  by  the  heart  alone,  cast  into  un- 
merited neglect. 

601 .  An  undue  acceleration  of  the  local  circulation,  arising  from  an 
excess  of  functional  activity  in  the  part,  and  unaccompanied  by  any 
other  change,  constitutes  the  state  known  as  active  congestion.^  or  deter- 
mination of  blood.  This  may  be  artificially  produced  by  the  applica- 
tion of  gentle  stimulants ;  and  it  is  usually  the  first  change  that  occurs, 
when  their  action  proves  sufficiently  violent  to  produce  Inflammation. 
From  that  state,  however,  it  is  distinguished  by  this  important  charac- 
ter,— that  there  is  merely  an  exaltation  of  the  natural  function,  but  no 
change.  Moreover  we  shall  presently  see  that,  in  Inflammation,  there 
is  a  stagnation  of  blood,  not  an  acceleration.  We  frequently  meet 
with  cases,  in  which  this  active  congestion  becomes  very  raanifest ; 
especially  in  persons  of  active  minds,  who  exert  their  mental  powers 
too  violently,  and  who  thereby  induce  an  habitually-increased  flo^v  of 
blood  towards  the  head,  manifested  in  the  increased  pulsation  of  the 
carotids,  the  suffusion  of  the  face  and  eyes,  and  the  heat  of  the  surface. 
The  balance  of  the  circulation  being  thus  disturbed,  there  is  almost 
invariably  a  diminished  energy  of  the  movement  of  blood  in  other 
organs,  especially  the  extremities  ;  as  indicated  by  their  habitual  cold- 
ness and  lividity.  In  the  treatment  of  such  a  state  (which  is  often 
the  precursor  of  serious  disease),  it  should  be  our  object  to  restore  the 
circulation  in  the  extremities,  by  friction,  exercise,  &c. ;  and  to  abate 
the  flow  of  blood  towards  the  head,  by  restraining  the  functional  activity 
of  the  brain,  by  the  application  of  cold  to  the  surface,  by  keeping  the 
head  high  during  sleep,  and  other  means  of  similar  tendency. 

602.  There  is  another  condition  of  the  capillary  circulation,  also 
known  under  the  name  of  Congestion,  which  is  precisely  the  opposite 
of  the  preceding.  In  this  state,  there  is  deficient  functional  energy  in 
the  part,  and  the  circulation  through  it  is  consequently  retarded, — as 
in  the  lungs  where  there  is  a  partial  obstruction  to  the  aeration  of  the 
blood.  The  same  cause  produces  a  deficient  tonicity  of  the  Arteries, 
and  allows  their  walls  to  be  unduly  distended  by  the  vis  a  tergo  of  the 
blood ;  and  consequently  there  is  a  great  accumulation  of  blood  in  the 
part,  with  a  retarded  movement.  This  condition,  like  the  preceding, 
predisposes  to  Inflammation,  although  in  a  different  mode,  as  will  be 
explained  hereafter  (§  631).  It  is  relieved  by  causes  which  promote 
the  action  of  the  part ;  thus  congestion  of  the  lungs,  occasioned  by  the 
effusion  of  fluid  into  the  air-cells,  which  creates  an  obstacle  to  the  aera- 
tion of  the  blood,  disappears  when  that  effusion  is  absorbed.  And 
congestion  of  the  liver,  the  result  of  deficient  secreting  power  in  the 
organ,  is  relieved  by  mercurial  and  other  medicines,  which  promote  the 
flow  of  bile  by  stimulating  the  growth  of  the  hepatic  cells. 

603.  The  Capillaries,  like  the  Arteries,  possess  a  power  of  contrac- 
tion and  dilatation,  which  seems  to  be  very  much  under  the  influence  of 
the  Nervous  System,  and  particularly  of  that  part  of  it  which  conveys 
the  influence  of  the  Emotions.     We  have  a  visible  example  of  this  in- 


MOVEMENT  OF  BLOOD  IN  THE  VEINS.  339 

fluence  in  the  act  of  blushing^  which  consists  in  a  sudden  enlargement 
of  the  capiUaries  and  small  vessels  of  the  surface ;  whilst  the  converse 
state  of  pallor,  which  often  alternates  with  it  under  the  influence  of 
strong  emotion,  is  evidently  due  to  an  unusual  contraction  of  the  same 
vessels.  But  the  effects  of  this  influence  are  no  less  sensible  in  other 
cases;  and  particularly  in  the  regulation  of  the  quantity  of  certain 
secretions,  in  accordance  with  the  mental  state,  or  the  condition  of  the 
system  generally.  To  the  mode  in  which  this  regulation  is  efiected,  the 
act  of  blushing  seems  to  afi'ord  us  the  key ;  for  it  indicates  that  the 
supply  of  blood  aff'orded  to  the  glands,  may  be  entirely  governed  by  the 
influence  of  the  nervous  system  upon  the  calibre  of  the  arteries.  Thus 
the  nursing  mother,  at  the  sight,  or  even  at  the  thought,  of  her  child, 
when  the  usual  time  for  suckling  approaches,  feels  a  rush  of  blood  to 
the  breast,  exactly  resembling  that  which  takes  place  to  the  cheeks  in 
blushing,  and  popularly  termed  "the  draught ;"  this  rush  occasions  an 
almost  immediate  increase  in  the  secretion.  In  like  manner  we  may 
explain  the  influence  of  the  mental  state  upon  the  amount  of  the  secre- 
tions of  the  lachrymal,  the  salivary,  and  many  other  glands  ;  its  influence 
upon  their  quality,  must  probably  be  efiected  through  changes  in  the 
condition  of  the  blood  itself. 

604.  The  supply  of  Nervous  agency  from  the  Cerebro-spinal  system, 
has  been  clearly  proved  to  exert  no  direct  influence  in  maintaining  the 
capillary  circulation  ;  since  the  latter  continues  as  usual,  after  all  the 
nerves  of  a  part  have  been  divided.  This  is  obviously  due  to  the  fact, 
that  the  operations  of  nutrition,  secretion,  &c.,  are  essentially  indepen- 
dent of  this  agency.  But  as  they  are  in  some  degree  influenced  by  it, 
so  will  the  capillary  circulation  be  afiected,  through  its  connexion  with 
them.  In  this  manner  we  are  to  explain  the  eff'ect  of  violent  impres- 
sions upon  the  nervous  centres  in  bringing  to  a  stand,  not  merely  the 
action  of  the  Heart  (§  581),  but  the  Capillary  circulation  all  over  the 
body.  The  general  vitality  of  the  system  appears  to  be  at  once  de- 
stroyed ;  so  that  the  capillary  circulation,  which  may  usually  be  seen  to 
continue  in  the  web  of  a  frog's  foot  for  some  time  after  the  interruption 
of  the  heart's  action,  is  immediately  suspended  by  crushing  the  brain 
with  a  hammer. 

6.    Of  the  Movement  of  Blood  in  the  Veins. 

605.  The  Venous  system  is  formed  by  the  reunion  of  the  small  trunks, 
which  originate  in  the  capillary  network ;  and  it  carries  'back  to  the 
heart  the  blood  which  has  been  transmitted  through  this.  This  blood  is 
dark  or  carbonated  in  the  systemic  veins;  whilst  it  is  bright  or  oxy- 
genated in  the  pulmonary  veins.  The  structure  of  the  veins  is  essen- 
tially the  same  with  that  of  the  arteries ;  but  the  fibrous  tissue  of  their 
middle  coat  less  decidedly  exhibits  the  characters,  either  of  the  yellow 
clastic  tissue,  or  of  non-striated  muscle.  Still  it  possesses  no  inconside- 
rable amount  of  Elasticity ;  and  a  certain  degree  of  Muscular  contrac- 
tility also.  The  whole  capacity  of  the  Venous  system  is  at  least  twice, 
and  perhaps  more  nearly  three  times,  that  of  the  Arterial ;  and  the 
rate  of  motion  of  the  blood  in  it  must  be  proportionably  slower. 


340  CIRCULATION   OF  NUTRITIVE  FLUID. 

606.  The  movement  of  the  Blood  through  the  Veins  is,  without  doubt, 
chiefly  effected  by  the  vis  a  t'ergo,  or  propulsive  force,  which  results  from 
the  contractile  power  of  the  heart  and  arteries,  aided  by  the  power 
generated  in  the  capillary  vessels.  The  intermittent  floAV,  which  is 
caused  by  the  interrupted  action  of  the  former,  is  usually  so  far  equalized 
during  the  passage  of  the  blood  through  the  capillary  network,  that  no 
pulsation  can  be  shown  to  exist  in  the  veins ;  but  instances  occasionally 
present  themselves,  in  which  a  venous  pulse  may  be  clearly  perceived. 
The  Venous  Circulation  is  affected,  however,  by  certain  other  causes, 
which  exert  little  influence  on  the  movement  of  blood  in  the  Arteries. 
One  of  these  is  the  frequently  recurring  action  of  Muscles,  to  which  the 
Veins  are  peculiarly  subject,  on  account  of  their  position.  In  every 
instance  in  which  Muscular  movement  takes  place,  a  portion  of  the 
Veins  of  the  part  will  undergo  compression ;  and  as  the  blood  is  pre- 
vented by  the  valves  in  the  veins,  from  being  driven  back  into  the  small 
vessels,  it  is  necessarily  forced  onwards  towards  the  heart.  As  each 
set  of  muscles  is  relaxed,  the  veins  that  were  compressed  by  it  fill  out 
again,  to  be  again  compressed  on  the  renewal  of  the  force.  Thus  we 
see  how  the  general  Muscular  movements  of  the  body  have  an  important 
influence  in  maintaining  the  Venous  Circulation, — how  continued  exer- 
cise, involving  the  alternate  contraction  and  relaxation  of  several  groups 
of  muscles,  must  send  the  blood  more  rapidly  towards  the  heart,  and 
thus  increase  the  rapidity  of  its  pulsations, — and  how  the  sudden  and 
simultaneous  action  of  a  large  number  of  muscles  after  repose  (as  when 
we  rise  up  from  the  sitting  or  lying,  to  the  standing  posture),  may  drive 
the  blood  to  the  heart  with' so  violent  an  impetus,  as  to  produce  even 
fatal  results,  if,  by  any  diseased  condition  of  that  organ,  it  should  be 
rendered  unable  to  dispose  with  sufficient  rapidity  of  the  quantity  of 
blood  thus  transmitted  to  it. 

607.  The  Respiratory  movements  exert  a  slight  influence  upon  the 
flow  of  blood  through  the  large  veins  near  the  heart ;  for  as  the  chest  is 
a  closed  cavity,  in  which  a  partial  vacuum  is  produced  by  the  act  of  In- 
spiration, whilst  its  contents  are  compressed  by  the  act  of  Expiration, 
the  former  state  will  favour  the  movement  of  blood  from  the  large  veins 
on  the  exterior  of  the  cavity,  towards  the  heart,  whilst  the  latter  condi- 
tion will  retard  it.  This  produces  the  phenomenon  termed  the  respira- 
tory pulse  ;  which  may  be  seen  in  the  veins  of  the  neck  and  shoulders  in 
thin  persons,  and  especially  in  those  who  are  suffering  from  pulmonary 
diseases.  The  influence  of  the  Respiratory  movements  is  made  evident 
by  introducing  a  tube  into  the  Jugular  vein,  the  lower  end  of  which 
dips  into  water ;  for  an  alternate  elevation  and  depression  of  the  water 
into  the  tube  is  then  witnessed,  showing  the  suction  power  of  the  Inspi- 
ratory movement,  and  the  expellent  force  of  the  Expiratory  act.  On 
the  other  hand,  the  Expiratory  movement,  while  it  directly  tends  to 
cause  accumulation  in  tlie  veins,  will  assist  the  heart  in  propelling  the 
blood  in  the  Arteries ;  and  by  the  combined  action  of  these  two  causes 
is  produced,  among  other  effects,  the  rising  and  sinking  of  the  Brain, 
synchronously  with  expiration  and  inspiration,  which  are  observed  when 
a  portion  of  the  cranium  is  removed. 

608.  A  pulsatory  movement  may  be  occasioned  in  the  great  veins 


RESPIRATORY   PULSE — VENOUS   PULSE.  341 

n6ar  the  heart,  by  another  cause  entirely  distinct  from  the  preceding; 
namely,  the  regurgitation  of  blood  from  the  ventricle  into  the  auricle,  and 
thence  into  the  vense  cavse,  during  the  ventricular  systole ;  and  the  pul- 
sation thus  occasioned  is  synchronous,  therefore,  with  that  in  the  arteries 
(proceeding  backwards,  however,  from  the  heart),  instead  of  correspond- 
ing with  the  respiratory  movement.  This  regurgitation  may  take  place, 
not  from  any  disease  in  the  valves  on  the  right  side  of  the  heart,  but 
simply  from  over-distension  of  its  cavities,  resulting  from  any  obstruc- 
tion to  the  circulation  of  blood  through  the  lungs ;  for  when  this  occurs, 
the  tricuspid  valve  does  not  completely  close,  and  allows  a  portion  of 
the  blood  to  escape  from  the  ventricle  backwards  into  the  auricle  and 
venae  cavse.  This  want  of  complete  closure,  constituting  what  has  been 
termed  the  "  safety-valve  function"^  of  the  tricuspid  valve,  has  been  par- 
ticularly noticed  in  diving  animals,  in  which  the  circulation  through  the 
lungs  is  liable  to  be  temporarily  suspended.  The  venous  pulsation 
which  is  thus  produced,  may  be  noticed  in  almost  every  case  of  long- 
standing dyspnoea ;  especially  when  this  is  accompanied  (as  it  usually 
is)  by  hypertrophy  and  dilatation  of  the  right  ventricle  of  the  heart. 

609.  The  Venous  circulation  is  much  more  liable  than  the  Arterial, 
to  be  influenced  by  the  force  of  Gravity  ;  and  this  influence  is  particu- 
larly noticeable,  when  the  tonicity  of  the  vessels  is  deficient.  The  fol- 
lowing experiments  performed  by  Dr.  WilliamSj  to  elucidate  the  influence 
of  deficient  firmness  in  the  walls  of  the  vessels,  and  of  gravitation,  over 
the  movement  of  fluids  through  tubes,  throw  great  light  on  the  causes 
of  Venous  Congestion.  A  tube  with  two  equal  arms  having  been  fitted 
to  a  syringe,  a  brass  tube  two  feet  long,  having  several  right  angles  in 
its  course,  was  adapted  to  one  of  them,  whilst  to  the  other  was  tied  a 
portion  of  a  rabbit's  intestine  four  feet  long,  and  of  calibre  double  that 
of  the  brass  tube,  this  being  arranged  in  curves  and  coils,  but  without 
angles  and  crossings.  When  the  two  ends  were  raised  to  the  same 
height,  the  small  metal  tube  discharged  from  two  to  five  times  the 
quantity  of  water  discharged  in  a  given  time  by  the  larger  but  mem- 
branous tube ;  the  difference  being  greatest,  when  the  strokes  of  the 
piston  were  most  forcible  and  sudden,  by  which  the  intestine  was  much 
dilated  at  its  syringe  end,  but  conveyed  very  little  more  water.  When 
the  discharging  ends  were  raised  a  few  inches  higher,  the  difference  inr 
creased  considerably,  the  amount  of  fluid  discharged  by  the  gut  being 
much  diminished ;  and  when  the  ends  were  raised^to  the  height  of  eight 
or  ten  inches,  the  gut  ceased  to  discharge,  each  stroke  only  moving  the 
column  of  water  in  it,  and  this  subsiding  again,  without  rising  nigh 
enough  to  overflow.  When  the  force  of  the  stroke  was  increased,  the 
part  of  the  intestine  nearest  the  syringe  burst. 

610.  From  these  experiments  it  is  easy  to  understand,  how  any  defi- 
ciency of  tone  in  the  Venous  system  will  tend  to  prevent  the  ascent  of 
the  blood  from  the  depending  parts  of  the  body,  and  will  consequently 
occasion  an  increased  pressure  on  the  walls  of  the  vessels,  and  an  aug- 
mentation in  the  quantity  of  blood  they  contain.  All  these  conditions 
are  peculiarly  favourable  to  the  escape  of  the  watery  part  of  the  blood 
from  the  small  vessels ;  and  this  may  either  infiltrate  into  the  areolar 
tissue,  or  it  may  be  poured  into  some  neighbouring  serous  cavity,  pro- 


342  CIRCULATION   OF   NUTRITIVE  FLUID. 

ducing  dropsy.  Thus  it  happens,  that  such  effusions  may  often  be 
traced  to  that  state  of  deficient  vigour  of  the  system,  which  peculiarly 
manifests  itself  in  want  of  tone  of  the  blood-vessels ;  and  that  it  is  relieved 
by  remedies  which  tend  to  restore  this.  In  many  young  females  of 
leuco-phlegmatic  temperament,  for  example,  there  is  a  tendency  to 
swelling  of  the  feet,  by  oedematous  effusion  into  the  areolar  tissue,  in 
consequence  of  the  depending  position  of  the  limbs ;  the  oedema  disap- 
pears during  the  night,  but  returns  during  the  day,  and  is  at  its  maxi- 
mum in  the  evening.  And  the  congestion  which  frequently  manifests 
itself  in  the  posterior  parts  of  the  body,  towards  the  close  of  exhausting 
diseases,  in  which  the  patient  has  lain  much  upon  his  back,  is  attributable 
to  a  similar  cause ;  of  such  congestion,  effusions  into  the  various  serous 
cavities  are  frequent  results ;  and  such  effusions,  taking  place  during 
the  last  hours  of  life,  are  often  erroneously  regarded  as  the  cause  of 
death.  To  the  same  cause  we  are  to  attribute  the  varicose  state  of  the 
veins  of  the  leg,  which  is  so  common  amongst  persons  of  relaxed  fibre, 
and  especially  in  those  whose  habits  require  them  to  be  much  in  the  erect 
posture ;  and  this  distension  occasionally  proceeds  to  complete  rupture, 
the  causes  of  which  are  fully  elucidated  by  the  experiments  just  cited. 

611.  It  has  been  thought  that  the  circulation  within  the  Cranium 
takes  place  under  different  conditions  from  that  of  other  parts  of  the 
body.  For  as  the  cranium  is  a  closed  cavity, — a  certain  part  of  which 
is  occupied  by  the  cerebral  substance  and  its  membranes,  the  remain- 
der being  filled  up  with  blood, — it  has  been  argued  that  the  amount 
of  blood  in  the  vessels  of  the  brain  must  be  always  the  same ;  and 
that  any  disturbance  of  its  circulation  must  be  due  to  a  difference  in 
the  relative  quantity  of  blood  in  the  arteries  and  the  veins.  This 
idea  appeared  to  derive  support  from  the  results  of  experiments,  which 
showed  that  the  blood  is  retained  in  the  vessels  within  the  cranium  of 
animals  bled  to  death,  unless  an  opening  be  made  in  the  skull,  so  as 
to  allow  the  air  to  exert  the  same  pressure  upon  these  vessels,  as  upon 
those  of  other  parts.  But  such  experiments  do  not  at  all  sanction  the 
assertion,  that  the  quantity  of  blood  within  the  cranium  is  constant ; 
on  the  contrary,  we  have  reason  to  believe  that  it  undergoes  as  much 
change  as  in  other  parts.  For  although  the  cerebral  substance  be 
incompressible,  yet  its  bulk  is  subject  to  constant  variation,  according 
to  the  quantity  of  fluid  it  contains  ;  and  the  presence  of  the  cerebro- 
spinal fluid  in  the  sub-arachnoid  cavity  of  the  brain  and  spinal  cord, 
appears  to  be  peculiarly  destined  to  favour  this  continual  change, — the 
proportions  of  it  contained  in  the  spinal  and  the  cerebral  cavities,  re- 
spectively, being  governed  by  the  bulk  of  the  other  contents  of  the 
cranium.  Thus  if  the  vessels  of  the  cerebrum  be  in  their  ordinary  state 
of  fulness,  a  certain  amount  of  fluid  is  present  in  the  sub-arachnoid 
cavity  of  the  brain  ;  this  will  be  pressed  out  into  the  spinal  portion  of 
the  cavity,  if  the  cerebral  vessels  be  unusually  distended  with  blood  ; 
whilst  it  will  be  increased  from  the  latter  source,  so  as  to  fill  up  the 
vacant  space  within  the  cranium,  if  the  cerebral  vessels  be  unusually 
empty. 


OF   NUTRITION.  343 


CHAPTER  VII. 


OP   NUTRITION. 

1.  Selecting  Power  of  the  Individual  Parts. 

612.  The  Blood  which  is  carried  into  the  different  parts  of  the 
system,  by  the  Circulating  apparatus,  is  the  source  from  which  all  the 
organs  and  tissues  of  the  body  derive  the  materials  of  their  growth  and 
development ;  and,  as  we  have  seen,  it  is  distributed  by  the  Capillaries 
of  the  several  tissues,  with  a  degree  of  minuteness,  which  varies  accord- 
ing to  the  activity  of  the  nutrient  operations  taking  place  in  the  indi- 
vidual parts.  Thus,  in  Nerve  and  Muscle,  Mucous  Membrane  and 
Skin,  a  constant  decay  of  the  old,  and  a  development  of  new  tissue,  are 
taking  placcj  when  these  organs  are  in  a  state  of  functional  activity ; 
and  a  copious  supply  of  blood  is  carried  through  every  part  of  their 
substance:  whilst  in  Cartilage  and  Bone,  Tendon  and  Ligament,  the 
amount  of  interchange  is  very  small,  and  is  effected  by  a  much  less 
minute  reticulation  of  capillary  blood-vessels. 

613.  The  materials  of  the  nutritive  process  being  prepared  in  the 
blood,  the  process  of  nutrition  is  the  act  of  each  individual  part ;  which 
grows  and  developes  itself,  in  virtue  of  its  own  inherent  powers,  as  long 
as  the  requisite  conditions  are  supplied.  The  mode  in  which  this  takes 
place,  in  each  individual  tissue,  has  been  already-  explained  in  the  for- 
mer part  of  this  Treatise.  We  have  seen  that,  in  the  great  majority 
of  cases,  the  act  of  Nutrition  is,  in  fact,  a  process  of  cell-growth ;  and 
that  it  takes  place  under  the  same  conditions  as  the  production  of  the 
simple  isolated  cell,  which  constitutes  the  whole  of  the  humblest  forms 
of  Cryptogamic  Vegetation, — namely,  that  it  grows  from  a  germ,  which 
draws  to  itself  the  materials  of  its  nutrition,  and  gives  to  some  of  them 
a  new  arrangement,  whereby  they  form  the  cell-wall,  whilst  others  are 
introduced  into  the  cell-cavity,- — and  that  when  it  has  passed  through 
its  regular  series  of  changes,  it  dies,  and  sets  free  its  contents.  We 
have  seen  that,  in  some  cases,  the  germs  are  prepared  by  previously- 
existing  cells  of  the  same  kind ;  whilst  in  others  they  are  furnished  by 
certain  "  nutritive  centres,"  which  seem  to  be  constantly  engaged  in 
the  preparation  of  them,  deriving  their  materials  from  the  blood.  Fre- 
quently it  would  seem  as  if  the  original  or  parent-cell  is  able  to  con- 
tinue the  production  of  secondary  cells  to  an  unlimited  extent,  even 
though  it  may  have  itself  undergone  a  considerable  change  of  form. 
Thus  the  ultimate  follicles  of  Glands  seem  to  be  at  first  closed  cells, 
which  subsequently  open  at  the  part  nearest  to  the  duct,  and  establish 
a  connexion  with  it ;  and  having  thus  changed  their  condition,  they  go 
on  developing  new  generations  of  secreting  cells  in  their  interior,  from 
their  own  nuclei  or  germinal  centres,  to  an  unlimited  extent.  In  like 
manner,  the  parent-cells  of  Muscular  Fibre,  which  have  coalesced  to 
form  the  tubular  Myolemma,  seem  to  continue  to  develope  new  fibrillae 
from  their  nuclei,  notwithstanding  their  change  of  form. 


344  OF   NUTRITION. 

614.  The  selecting  power,  which  is  possessed  by  the  germs  of  each 
kind  of  tissue,  and  which  enables  them  to  draw  from  the  blood  the 
materials  which  they  severally  require  for  their  development,  manifests 
itself  also  in  the  mode  in  which  substances,  that  are  abnormally  present 
in  the  blood,  affect  the  condition  and  development  of  the  solid  tissues. 
Thus  we  find  that  the  presence  of  a  certain  quantity  of  Arsenic  in  the 
blood,  will  produce  a  state  of  irritation  in  all  the  Mucous  membranes  of 
the  body.  The  continued  introduction  of  Lead  into  the  circulating 
system,  occasions  a  modification  in  the  nutrition  of  the  extensor  muscles 
of  the  fore-arm,  producing  the  form  of  partial  paralysis  commonly 
termed  "wrist-drop,"  and  the  existence  of  this  modification  is  shown 
by  the  presence  of  lead  in  the  palsied  muscles.  Here  we  have  to 
remark  the  symmetrical  nature  of  the  affection,  consequent  upon  the 
occurrence  of  the  same  disorder  in  the  corresponding  parts  of  the  two 
sides  of  the  body ;  for  these  muscles  appear  to  have  the  same  kind  of 
tendency  to  attract  lead  from  the  circulating  current,  in  a  degree  that 
is  equal  on  the  two  sides,  as  they  have  to  draw  from  the  blood  the 
materials  of  their  regular  growth,  and  to  develope  themselves  in  an 
exactly  similar  manner.  In  like  manner,  the  cutaneous  eruptions,  which 
are  occasionally  produced  by  the  internal  exhibition  of  iodide  of  po- 
tassium, are  found  to  be  almost  precisely  symmetrical :  the  presence  of 
the  medicine  in  the  blood  being  the  occasion  of  a  disordered  nutrition 
of  certain  parts  of  the  skin  ;  and  the  selecting  power  of  particular  spots 
being  evinced,  by  the  exact  correspondence  of  the  parts  affected  on  the 
two  sides. 

615.  The  same  appears  to  be  the  case  with  regard  to  substances, 
whose  presence  in  the  blood  is  rather  the  result  of  a  disordered  condi- 
tion of  the  digestive  and  assimilating  processes,  than  of  their  direct 
introduction  fi-om  without.  Thus  in  Lepra  and  Psoriasis,  —  chronic 
diseases  of  the  Skin,  which  seem  to  have  their  origin  in  a  disordered 
state  of  the  blood,  rather  than  in  the  solid  tissues  affected, — we  find  a 
remarkable  tendency  to  the  repetition  of  the  patches  on  the  two  sides 
of  the  body,  or  on  the  corresponding  parts  of  the  limbs  ;  and  this  we 
must  attribute  to  the  peculiar  attraction,  existing  between  the  solid 
tissues  of  those  parts,  and  the  morbid  matter  circulating  through  them. 
So  in  those  chronic  forms  of  Gout  and  Rheumatism,  which  modify  the 
nutrition  of  the  joints,  producing  a  deposit  of  "chalk-stones,"  or  per- 
manent distortion  and  stiffening,  we  almost  invariably  find  the  corre- 
sponding joints  of  the  two  sides  affected.  The  chief  exceptions  to  the 
general  principle,  that  the  presence  of  morbid  or  extraneous  matters  in 
the  blood  affects  corresponding  parts  alike,  are  found  to  exist  where 
there  is  much  febrile  disturbance,  or  where  local  causes  produce  a 
peculiar  tendency  to  disorder  of  a  single  part.  The  nearer- the  character 
of  the  morbid  process  is  to  that  of  the  ordinary  nutritive  operations,  the 
more  nearly  does  it  approach  these,  in  the  symmetry  with  which  it 
developes  itself.* 

*  See  Dr.  W.  Budd's  valuable  Paper  on  the  ♦' Symmetry  of  Disease,"  in  vol.  xxv.  of 
the  Medico-Chirurgical  Transactions. 


VARYING  ACTIVITY  OF   THE   NUTRITIVE   PROCESSES.  345 


2.    Varying  Activity  of  the  Nutritive  Processes. 

616.  The  nutritive  operations  go  on  with  very  great  variations  in 
their  relative  activity,  under  different  circumstances.  As  a  general 
rule  it  may  be  stated  that,  the  greater  the  demand  for  the  functional 
activity  of  the  organ  or  tissue,  the  more  energetic  is  its  nutrition ;  and 
vice  versd.  Now  this  is  readily  underwood,  when  it  is  considered,  that 
the  active  state  of  many  structures  essentially  consists  in  an  act  of 
nutrition ;  thus  the  energy  of  the  secreting  processes  is  really  de- 
pendent, as  we  have  seen,  upon  the  growth  of  the  secreting  cells,  which 
make  up  the  essential  part  of  the  gland,  and  the  energy  of  the  absorb- 
ing and  assimilating  processes  is  dependent  upon  the  development  of 
the  cells,  which  select  and  elaborate  the  nutrient  matter.  This  growth 
is  regulated  mainly  by  the  supply  of  blood ;  being  increased  by  the 
afflux  of  blood  towards  the  part,  in  consequence  of  the  influence  of  the 
nerves  upon  the  vessels,  or  through  any  other  change  in  the  current  of 
the  circulation.  Thus  the  secretions  are  increased  in  amount,  by  emo- 
tions of  the  mind,  that  act  (probably  through  the  sympathetic  nerve)  in 
regulating  the  calibre  of  the  arteries  supplying  their  respective  glands : 
or  the  interruption  of  the  function  of  one  gland  shall  occasion  an 
increased ,  nutrition,  and  consequently  an  augmented  secretion,  in  its 
fellow, — as  when  one  of  the  kidneys  is  hypertrophied,  through  a  dis- 
ease in  the  other,  that  renders  it  incapable  of  performing  its  office. 
Still  it  would  appear,  that  there  may  be  variations  in  the  activity  of 
these  organs,  resulting  from  causes  inherent  in  themselves  (of  the 
nature  of  which  we  know  little  or  nothing) ;  and  that  here,  as  else- 
where, active  nutritive  operations  will  promote  the  circulation  of  blood 
through  the  parts,  whilst  a  languid  state  of  the  function  will  retard  it. 

617.  In  certain  other  tissues,  however,  the  functional  activity  would 
seem  to  consist  rather  in  a  waste  Or  decay  of  structures  previously 
developed ;  this  is  the  case  especially  in  Nerve  and  Muscle,  which  are 
found  to  undergo  disintegration,  in  exact  proportion  to  the  degree  in 
which  they  are  exercised ;  whilst  the  degree  in  which  this  waste  is 
repaired,  depends  upon  the  supply  of  nutritive  material,  the  quiescent 
state  of  the  part,  and  other  circumstances.  But  even  here  we  find 
that  functional  activity  occasions  increased  nutrition;  in  the  same 
manner  as  burning  a  lamp  with  a  high  flame  increases  the  amount  of 
fluid  drawn  up  by  the  wick.  For  neither  the  ne/ves  nor  the  muscles 
can  act  with  energy,  without  a  large  supply  of  arterial  blood ;  and  this 
is  drawn  to  them  on  the  principles  already  mentioned  (§  600)  as  in- 
creasing the  energy  of  the  local  circulation.  The  determination  of 
blood  to  the  parts,  thus  established,  favours  their  increased  nutrition ; 
and  thus  we  find  that,  under  favourable  circumstances,  any  set  of 
Muscles,  which  is  habitually  exercised,  undergoes  a  great  increase  of 
development ;  whilst,  in  like  manner  the  Nervous  centres,  if  too  great  a 
demand  be  made  upon  their  activity,  are  liable  to  become  hypertrophied 
(especially  in  young  persons),  and  may  thus  become  subject  to  disorders, 
which  temporarily  or  permanently  destroy  their  powers.  In  these  cases, 
then,  the  functional  activity  determines  the  increased  supply  of  blood, 
and  occasions  the    augmented   growth;    and  increased   nutrition  will 


846  OF  NUTRITION. 

rarely  take  place  in  these  tissues  without  an  especial  stimulus  of  this 
kind.  Thus  we  find  that,  when  a  larger  supply  of  nutritive  matter  is 
introduced  into  the  circulation,  than  is  required  to  repair  the  waste  of 
these  tissues,  they  do  not  undergo  an  increased  development  in  conse- 
quence ;  but  an  augmented  nutrition  is  produced,  either  in  the  adipose 
tissue,  or  in  the  glandular  structures  by  which  the  superfluous  matter  is 
eliminated  from  the  system. 

618.  Augmented  nutrition,  or  Hypertrophy^  then,  may  result  in  cer- 
tain organs,  from  an  excessive  supply  of  their  nutrient  materials ;  as  in 
the  case  of  the  kidney,  just  mentioned ;  or  as  in  the  enlargement  which 
we  not  unfrequently  meet  with  in  the  livers  of  those,  who  have  resided 
long  in  warm  climates,  and  who  have  not  sufficiently  restricted  their 
supply  of  non-azotized  food  to  the  small  amount  required  for  respiration 
at  an  elevated  temperature,  thereby  sending  an  over-supply  of  that  par- 
ticular class  of  bodies,  to  be  separated  from  the  blood  by  the  liver. 
Or,  in  other  cases,  the  increase  of  functional  activity  may  be  the  imme- 
diate cause  of  the  increased  nutrition ;  and  this  we  see,  not  only  in  the 
Uervous  centres  and  voluntary  muscles,  which  are  put  in  action  by  the 
will,  but  in  parts  over  which  the  mind  has  no  control.  Thus  the  heart 
becomes  hypertrophied,  when  an  obstruction  exists  in  the  pulmonary  or 
systemic  circulation,  to  overcome  which,  increased  energy  of  contraction 
is  required ;  and  in  the  same  manner  the  muscular  coats  of  the  urinary 
and  gall-bladder  acquire  an  extraordinary  increase  of  thickness,  when 
long-continued  obstruction,  by  calculi  or  stricture  in  the  canals  issuihg 
from  them,  impedes  the  free  exit  of  their  contents.  Sometimes,  how- 
ever, a  local  hypertrophy  takes  place,  which  cannot  be  accounted  for  in 
either  of  these  modes ;  as  wh6n  a  single  finger  is  enlarged  out  of  all 
proportion  to  the  rest,  or  the  whole  of  one  hand  increases  to  a  much 
greater  size  than  the  other,  by  the  existence  (as  it  would  seem)  in  the 
individual  part  of  that  tendency  to  unusual  development,  which,  when  it 
affects  the  whole  body  uniformly,  produces  a  gigantic  stature. 

619.  Now  a  precisely  reversed  series  of  conditions  diminishes  the 
activity  of  the  nutrient  processes,  and  induces  a  state  of  Atrophy, 
If  there  be  a  deficiency  in  the  general  amount  of  nutriment  introduced 
into  the  system  by  absorption,  a  general  atrophy  results ;  and  the  waste 
being  more  rapid  than  the  supply,  there  is  a  diminution  in  the  volume 
of  all  the  tissues  excepting  the  nervous,  which  seems  to  have  its  nutri- 
tion kept  up  even  to  the  last,  at  the  expense  of  all  the  rest.  Such  a 
condition  results  not  merely  from  the  want  of  food,  but  also  from  the 
want  of  power  to  assimilate  it ;  and  thus  emaciation  may  take  place 
to  an  excessive  degree,  when  food  of  the  most  nutritive  character  is 
copiously  supplied,  and  when  the  appetite  for  it  is  vehement ;  in  conse- 
quence of  disorder  in  the  mesenteric  glands,  or  in  some  other  part  of 
the  apparatus  particularly  concerned  in  the  elaboration  of  fibrine.  A 
partial  atrophy  may  result,  in  like  manner,  from  a  deficiency  of  the 
materials  required  for  the  formation  of  an  individual  tissue  or  organ ; 
thus  the  adipose  tissue  throughout  the  body,  may  be  atrophied,  in  con- 
sequence of  an  absence  of  those  materials  in  the  food,  which  are  capable 
of  being  converted  into  fatty  matter.  Or  a  particular  organ  may  be 
atrophied,  by  a  diminution  of  the  circulating  current  that  should  flow 


I 


VARYING  ACTIVITY  OF  THE  NUTRITIVE  PROCESSES.  347 

to  it,  either  in  consequence  of  obstruction  in  the  trunk,  or  by  the  par- 
tial diversion  of  the  stream  of  blood  in  another  direction ;  thus  the  liver, 
which  is  much  more  developed  in  the  foetus,  relatively  to  the  rest  of  the 
body,  than  it  is  in  the  adult,  undergoes  a  partial  atrophy  immediately 
after  birth,  in  consequence  of  the  change  in  the  whole  course  of  the  cir- 
culation, which  takes  place  as  soon  as  the  lungs  are  expanded. 

620.  But  partial  atrophy  may  also  take  place  from  causes  inherent 
in  a  particular  organ.  Thus  we  occasionally  meet  with  limbs,  which 
are  "  blighted,"  never  attaining  their  due  size  relatively  to  the  remainder 
of  the  body,  yet  not  exhibiting  any  defect  of  organization.  Here  there 
would  seem  to  be,  from  some  unknown  cause,  a  deficient  power  of 
growth ;  analogous  to  that  which,  when  acting  on  the  body  in  general, 
confines  it  within  dwarfish  dimensions. — One  of  the  most  frequent  causes 
of  partial  atrophy,  however,  is  want  of  functional  activity  in  the  organ ; 
and  this  is  particularly  the  case  in  regard  to  the  Muscular  and  Nervous 
systems.  Thus,  as  already  remarked  (§  348),  any  set  of  Muscles  that 
is  long  disused,  becomes  partially  atrophied ;  which  is  probably  due  to 
the  feebleness  and  languor  of  the  circulation,  consequent  upon  the 
absence  of  the  demand  for  arterial  blood.  As  soon  as  the  parts  are 
called  into  use  again,  their  nutrition  improves.  So,  also,  in  regard  to 
the  Nerves ;  the  nutrition  of  both  the  fibrous  and  vesicular  structures 
appears  to  be  entirely  dependent  upon  the  activity  of  their  function ; 
and  as  the  former  are  inert  without  the  latter,  we  may  say  that  the  due 
nutrition  of  the  nervous  system  entirely  depends  upon  the  functional 
activity  of  the  vesicular  matter.  Of  this  we  have  a  well-marked  illus- 
tration in  the  fact,  that  when  the  cornea  has  been  rendered  so  opaque 
by  disease  or  accident,  as  to  prevent  the  penetration  of  any  light  to  the 
interior  of  the  eye,  the  retina  and  the  optic  nerve  lose  after  a  time  their 
characteristic  structure  ;  so  that  scarcely  a  trace  of  the  peculiar  globules 
of  the  former,  or  of  the  nerve-tubes  of  the  latter  can  be  found  in  them. 

621.  In  the  healthy  condition  of  the  organism,  however,  the  nutri- 
tion, in  every  part  of  the  body  goes  on  in  a  degree  sufficient  to  keep  it 
constantly  ready  for  the  performance  of  its  appropriate  function  ;  a 
regular  supply  of  the  requisite  materials  being  furnished  in  the  aliment, 
and  being  prepared  by  the  assimilating  processes ;  and  the  products  of 
the  waste  or  decay  of  the  tissues,  together  with  such  alimentary  mate- 
rials as  may  be  superfluous,  being  carried  ofi"  by  the  excreting  opera- 
tions. When  the  nutrition  and  the  waste  are  eqfual,  the  weight  of  the 
body  remains  the  same ;  and  this  is  commonly  the  case  in  adult  age. 
But  during  the  earlier  periods  of  life,  the  powers  of  growth  are  greater ; 
the  demand  for  food  is  very  large  in  proportion  to  the  bulk  of  the  body ; 
and  though  the  waste  is  rapid,  and  the  excreting  processes  very  active 
(as  evinced  by  the  large  amount  of  urea  and  of  carbonic  acid  set  free), 
the  growth  predominates  over  the  decay,  and  the  development  of  the 
whole  structure  proceeds  at  a  gradually-decreasing  rate,  until  the  full 
stature  and  bulk  are  attained.  The  energy  of  the  nutritive  process  is 
particularly  manifested,  in  the  rapidity  and  completeness  with  which 
severe  injuries,  occasioned  by  disease  or  accident,  are  repaired.^  In 
advanced  life,  on  the  contrary,  although  the  waste  is  comparatively 
small,  the  renewing  processes  are  enfeebled  in  a  still  greater  degree ; 


348  OF   NUTRITION. 

and  there  is  a  gradual  diminution  in  the  stature  and  bulk  of  the  body, 
and  in  its  physical  powers.  All  the  functions  are  performed  with  de- 
creased energy  ;  and  the  comparative  inertness  of  the  nutritive  processes 
is  seen  in  the  diflficulty  with  which  the  effects  of  severe  injuries  are 
repaired,  in  the  length  of  time  requisite  for  the  purpose,  and  frequently 
in  the  imperfection  of  the  result. 

622.  During  the  successive  periods  of  life,  there  are  many  remarkable 
changes  in  the  relative  nutrition  of  different  organs  ;  which  we  can  attri- 
bute to  nothing  else,  than  to  inherent  differences  in  their  own  powers  of 
development.  Thus,  during  the  early  stages  of  foetal  existence,  the 
greatest  energy  of  growth  is  seen  in  certain  parts  which  are  to  answer 
but  a  temporary  purpose,  and  which  are  afterwards  completely  atrophied. 
This  is  the  case,  for  example,  with  the  Corpora  Wolffiana,  which  seems 
to  answer  the  purpose  of  temporary  kidneys,  and  in  connexion  with 
which  the  permanent  kidneys  and  the  genital  organs  are  developed  ;  and 
of  these  bodies,  though  of  large  size  in  the  early  embryo,  and  evidently 
of  great  importance,  no  trace  whatever  is  afterwards  to  be  discovered. 
So  in  regard  to  the  Supra-Renal  capsules,  the  Thymus  and  Thyroid 
glands,  and  other  organs,  we  find  their  proportional  size  the  greatest, 
and  their  fun-ction  evidently  the  most  active,  during  foetal  existence  and 
in  early  infancy ;  after  which  their  bulk  diminishes  in  proportion  to  the 
rest  of  the  body,  and  their  functional  activity  seems  almost  at  an  end. 

623.  Even  in  the  relative  development  of  the  organs  which  form 
essential  parts  of  the  permanent  structure,  we  find  considerable  varia- 
tions at  different  periods  of  life.  Thus  the  evolution  of  the  generative 
system  does  not  usually  take  place,  until  the  rest  of  the  body  is 
approaching  its  maturity ;  but  cases  sometimes  occur,  in  which  this 
apparatus  attains  its  full  development,  both  in  the  male  and  the  female, 
at  a  very  early  period  of  childhood,  and  seems  capable  of  performing 
its  functions.  In  the  Human  species,  these  organs,  when  once  evolved, 
remain  always  in  a  state  of  preparation  for  the  performance  of  their 
function,  unless  they  are  atrophied  through  complete  disuse,  or  have 
lost  their  vigour  by  age,  or  through  excessive  demands  upon  their  acti- 
vity ;  but  in  most  of  the  lower  animals,  the  development  of  these  organs 
is  periodical  through  the  whole  of  life,  taking  place  at  a  certain  season 
of  the  year,  and  being  greatly  influenced,  it  would  appear,  by  the 
external  temperature,  and  by  the  supply  of  food.  Thus  in  the  Sparrow, 
the  testes  are  no  larger  than  mustard-seeds,  during  the  greater  part  of  the 
year ;  but  in  the  spring,  they  acquire  the  size  of  large  peas,  and  it  is 
then  only  that  they  possess  any  procreative  power. 

624.  We  are  not  always  to  judge  of  the  degree  of  development  of 
organs,  however,  by  their  size  alone  ;  for  the  completeness  of  their  struc- 
ture, and  their  aptitude  for  the  performance  of  their  functions,  must 
also  be  taken  into  the  account.  Thus  in  the  new-born  infant,  the  organs 
of  Digestion  and  Assimilation,  though  of  small  size,  are  so  completely 
formed  as  to  be  able  at  once  to  take  on  the  duty  of  receiving  and  pre- 
paring the  nutritive  materials,  provided  these  are  supplied  in  a  form 
adapted  to  their  powers ;  the  Circulating  apparatus  is  fully  adequate  to 
transmit  the  products  of  the  action  of  those  organs  to  the  body  in 
general,  and  to  bring  back  the  results  of  its  continual  decay ;  and  the 


VARIATIONS   OF  NUTRITION  WITH  AGE,  349 

Respiratory  organs,  together  with  other  parts  of  the  Excretory  appa- 
ratus, are  so  completely  evolved,  as  to  be  able  to  separate  the  effete 
matter,  and  to  cast  it  out  of  the  system  with  an  energy  equivalent  to 
that  of  the  organs,  by  which  new  matter  is  introduced  and  appropriated. 
On  the  other  hand,  the  Brain,  although  of  larger  comparative  size  at 
birth,  than  at  any  subsequent  period  of  life,  is  but  very  imperfectly 
developed ;  for  its  structure  is  not  yet  so  far  completed,  as  to  prepare 
it  for  a  state  of  high  functional  activity.  In  fact  it  would  seem  as  if 
the  use  of  the  organ,  as  called  forth  by  the  new  circumstances  in  which 
the  infant  is  placed  as  soon  as  it  comes  into  the  world,  is  essential  to 
its  complete  development ;  and  the  same  may  be  said  of  the  Muscular 
system. 

625.  During  the  whole  period  of  infancy  and  childhood,  the  current 
of  nutrition  seems  peculiarly  directed  towards  the  brain ;  for  though 
its  size  does  not  continue  to  increase,  in  proportion  with  that  of  the 
remainder  of  the  body,  its  structure  is  evidently  being  rendered  more 
perfect,  and  its  functional  activity  is  excited  with  remarkable  facility. 
Hence  it  is  peculiarly  liable  to  be  acted  on  by  various  causes  which 
may  produce  disease  ;  and  the  operation  of  remedies,  which  specially 
affect  that  organ,  is  far  more  powerful  than  at  any  other  period  of  life. 
Thus,  whilst,  a  child  will  bear  a  fourth,  or  even  a  third  of  the  dose  of  a 
purgative  adequate  for  an  adult,  it  is  strongly  affected  by  an  eighth,  or 
even  a  twelfth  of  the  dose  of  a  narcotic  or  a  stimulant  that  would  be 
required  to  produce  a  corresponding  effect  in  middle  life.  This  peculiar 
impressibility  of  the  nervous  system,  resulting  from  the  activity  of  the 
nutrient  processes  which  are  taking  place  in  it,  manifests  itself  also  in 
other  ways ;  thus  children  are  peculiarly  liable  to  have  its  powers  de- 
pressed by  any  sudden  shock,  such  as  a  blow,  or  an  extensive  burn  or 
laceration ;  whilst,  on  the  other  hand,  if  the  depression  be  not  fatal, 
they  recover  from  its  effects  much  more  speedily  than  an  adult  would 
do  from  a  similar  condition. 

626.  During  the  periods  of  youth  and  adolescence,  the  chief  energy 
of  development  (except  in  regard  to  the  generative  system,  already 
noticed,)  appears  to  be  directed  towards  the  Muscular  apparatus ;  which 
then  increases  in  vigour,  in  a  degree  which  surpasses  its  increase  of 
size ;  and  the  circulating  and  respiratory  organs,  upon  whose  energetic 
action  there  is  then  a  corresponding  demand,  are  peculiarly  liable  to 
disturbance  of  function,  inducing  disease  in  themselves  or  in.  other  parts. 
The  maladies  of  this  period  are  for  the  most  part  of  a  sthenic  or  inflam- 
matory character ;  resulting,  as  we  shall  presently  see,  from  the  exces- 
sive activity  of  the  assimilating  processes,  which  are  disposed  to  produce 
more  fibrine  than  the  wants  of  the  body  require.  Or  if,  on  the  other 
hand,  there  be  an  imperfect  elaboration  of  the  nutrient  materials,  as 
happens  in  the  tubercular  diathesis,  its  effects  are  peculiarly  liable  to 
manifest  themselves  at  this  period,  when  the  demand  for  nutritive  matter 
is  greatly  augmented  by  the  activity  of  the  muscular  system. 

627.  In  adult  age,  there  should  be  such  a  balance  of  all  the  functions, 
arising  from  the  due  development  and  proper  use  of  each  organ,  as  may 
preserve  the  body  in  the  state  of  health  and  vigour,  without  any  marked 
change  in  the  relative  dimensions  of  its  different  parts,  through  a  long 


350  OF  NUTRITION. 

series  of  years.  The  digestive,  assimilating,  and  excreting  organs,  as 
they  were  the  first  to  come  to  maturity,  are  commonly  the  first  to  fail 
in  their  activity ;  but  this  is  very  generally  the  result  of  over-exertion 
of  their  powers,  the  amount  of  food  introduced  into  the  stomach  being 
rarely  (among  the  higher  and  middle  classes  of  society  at  least)  kept 
down  to  the  real  wants  of  the  system.  The  muscular  apparatus  usually 
experiences  the  effects  of  this  diminished  nutrition,  sooner  than  the 
nervous  system ;  the  vigour  of  the  latter  being  often  sustained  in  a 
remarkable  degree  (as  shown  by  the  energy  of  the  mental  operations) 
through  a  protracted  life,  when  it  has  not  been  overtasked  at  an  earlier 
period.  The  very  slight .  impairment  of  the  nutrition  of  the  nervous 
system,  during  the  general  emaciation  which  results  from  a  wasting  dis- 
ease, or  during  that  more  gradual  decline  of  the  bodily  vigour  which  is 
consequent  upon  advancing  age,  is  a  phenomenon  which  strongly  marks 
it  -out  as  the  part  of  the  body,  to  the  maintenance  of  whose  integrity 
everything  else  is  subservient ;  and  this  is  still  more  remarkably  shown 
in  the  phenomena  of  starvation,  in  which  state,  notwithstanding  the  dis- 
appearance of  the  whole  of  the  fat,  and  the  reduction  of  the  weight  of 
the  body  in  general  by  about  40  per  cent.,  the  nervous  system  appears 
to  lose  little  or  none  of  its  substance  (§  117). 

3.    Of  Death,  or  Cessation  of  Nutrition. 

628.  The  general  cessation  of  the  Nutritive  operations,  in  Deaths 
usually  depends,  as  formerly  explained  (§  Qb)^  upon  the  cessation  of  the 
supply  of  Nutriment,  in  consequence  of  the  stagnation  of  the  Circulating 
current;  and  this  stagnation  may  result  from  the  direct  operation  of 
three  causes ;  namely, — failure  in  the  propulsive  power  of  the  Heart, 
or  Syncope, — obstruction  to  the  flow  of  blood  through  the  pulmonary 
capillaries,  consequent  upon  a  deficient  supply  of  air,  or  Asphyxia, — 
and  a  disordered  state  of  the  blood  itself  (§  534),  which  at  the  same 
time  weakens  the  power  of  the  heart,  and  prevents  the  performance  of 
those  changes  in  the  systemic  capillaries,  which  aff*ord  a  powerful 
auxiliary  to  the  circulation ;  a  mode  of  death,  for  which  the  term  Ne- 
crcemia  has  been  proposed.  Each  of  these  conditions  may  be  dependent 
upon  a  variety  of  remote  causes,  which  cannot  be  here  particularized. 
But  it  is  evident  that,  when  either  one  of  them  has  been  established,  the 
nutritive  processes  must  speedily  cease,  although  they  may  continue  for 
a  short  time  at  the  expense  of  the  blood  in  the  capillaries  of  the  part. 
The  cooling  of  the  body  is  another  cause  of  their  cessation ;  and  this 
is  one  reason  why  molecular  death  (or  the  death  of  the  individual  organs 
and  tissues)  follows  so  much  more  closely  on  somatic  death  (or  the  ces- 
sation of  the  circulating  and  respiratory  functions),  in  warm-blooded 
than  in  cold-blooded  animals.  In  either  case,  however,  the  solid  tissues 
may  preserve  for  a  time  their  independent  vitality ;  and  changes  may 
take  place  in  them,  which  indicate  the  continuance  of  their  nutritive 
actions  to  a  certain  extent,  even  when  they  have  been  disconnected  from 
the  body.  There  are  undoubtedly  cases,  however,  in  which  the  loss  of 
vital  power  is  as  complete  and  immediate  in  the  solids  as  in  the  fluids ; 
the  want  of  ability  to  avail  themselves  of  nutriment  being  as  decided  in 


VARIOUS  CAUSES  OF  DEATH.  351 

the  former,  as  the  deficiency  of  supply  is  in  the  latter.  This  is  seen, 
for  example,  when  death  results  from  a  sudden  and  violent  shock,  which 
destroys  the  vitality  of  the  whole  system  alike  (§  604) ;  molecular  death 
being  here  consentaneous  with  somatic. 

629.  But  as  each  component  part  of  the  Animal  fabric  has  an  indi- 
vidual life  of  its  own,  so  must  it  have  a  limited  duration  of  its  own  ;  the 
period  of  termination  of  its  vital  activity,  or  its  death,  being  quite  inde- 
pendent of  that  of  the  body  at  large,  excepting  in  so  far  as  the  opera- 
tions of  the  latter  are  requisite  to  afford  it  a  constant  supply  of  appro- 
priate nutriment,  and  to  maintain  its  temperature  at  the  proper  eleva- 
tion. It  is  perfectly  compatible,  on  the  other  hand,  with  the  Life  of 
the  entire  organism,  that  certain  parts  of  it  should  be  continually  in 
course  of  decay  and  renewal ;  and,  in  fact,  we  find  that  the  most  im- 
portant parts  in  the  vital  functions  are  performed  by  tissues  whose  indi- 
vidual duration  is  comparatively  brief,  but  which  are  renewed  as  fast  as 
they  degenerate.  We  have  a  well-marked  example  of  this  in  the  case 
of  the  leaves  of  trees,  which  are  the  chief  agents  in  the  preparation  of 
the  nutritious  fluid,  at  whose  expense  the  permanent  tissues  of  the  trunk 
and  branches  are  generated ;  and  although  there  is  nothing  in  the  Ani- 
mal body  at  all  comparable  to  the  complete  exuviation  which  commonly 
takes  place  in  the  Plant  at  the  close  of  the  season  of  vegetative  activity, 
yet  there  is  a  continual  death  and  separation  of  parts  that  have  per- 
formed their  function,  which  in  the  end  makes  up  a  much  larger  aggregate. 
Thus  there  is  scarcely  a  less  complete  renewal  of  the  epidermis  in  Man, 
in  the  course  of  twelve  months,  than  there  is  in  Serpents,  Frogs,  &c., 
which  throw  it  off  periodically ;  the  only  difference  being,  that  in  the 
one  case  the  whole  is  exuviated  and  renewed  at  once,  whilst  in  the  other 
there  is  a  continual  interchange.  In  the  exuviation  of  the  antlers  of 
the  Deer,  and  of  the  milk-teeth  of  all  Mammalia,  we  have  very  marked 
examples  of  this  limitation  of  the  life  of  individual  parts,  even  in  the 
highest  Animals ;  and  as  a  general  proposition  it  may  be  stated,  that 
every  part  must  degenerate,  when  it  has  gone  through  the  whole  series 
of  changes  in  which  its  Life  consists,  and  that  it  must  then  either  die 
and  decay,  or  must  be  so  altered  in  its  constitution,  as  to  be  able  to 
remain  inactive  without  further  change. 

630.  Hence  we  see  that  the  duration  of  vital  activity  must  be,  cceteris 
paribus,  in  the  inverse  ratio  of  its  energy ;  that  is,  the  life  of  any  part, 
or  of  the  entire  organism,  must  be  shortened  by^any  excess  of  func- 
tional activity ;  whilst  it  may  be  prolonged  by  such  a  degree  of  repose, 
as  does  not  involve  an  impairment  of  its  nutrition.  We  see  this  most 
remarkably  exemplified  in  the  case  of  cold-blooded  animals ;  the  dura- 
tion of  whose  lives,  after  they  have  sustained  some  fatal  injury  (such  as 
the  removal  of  the  heart  or  of  the  lungs),  or  are  placed  in  any  other 
circumstances  incompatible  with  its  continuance,  is  in  the  inverse  pro- 
portion to  the  elevation  of  the  temperature  to  which  they  are  exposed, 
and  therefore  to  the  degree  of  their  vital  activity  (§  128).  Now  although 
this  variation  is  comparatively  little  observable  in  the  rate  of  life  of  that 
portion  of  the  fabric  of  warm-blooded  animals  which  is  concerned  in 
their  organic  functions  (the  temperature  to  which  it  is  subjected  being 
nearly  constant),  it. is  clearly  seen  in  those  organs  whose  functional 


352  OF  NUTRITION. 

activity  is  more  under  the  control  of  the  individual,  and  is  therefore  less 
constant.  Thus,  in  Man,  we  continually  notice  that  the  duration  of  the 
powers  of  the  Brain  and  the  Generative  system  is  the  longest,  when 
these  organs  have  been  moderately  exercised ;  and  that  it  is  much  cur- 
tailed by  the  excessive  use  of  either.  The  duration  of  their  activity, 
however,  is  not  increased  by  partial  or  entire  disuse  of  the  organs ;  for 
this  induces  a  state  of  atrophy,  on  the  principles  already  mentioned. 
Now  we  have  every  reason  to  believe,  that  what  is  true  of  individual 
parts  and  organs,  is  true  also  of  the  whole  structure ;  and  that  the 
existence  of  the  entire  bodily  fabric  may  thus  come  to  an  end,  without 
any  special  disease,  in  consequence  of  the  limit  originally  set  to  its 
powers  of  self-renovation.  It  is  but  rarely,  however,  that  this  occurs ; 
the  various  accidents  of  life,  the  neglect  of  ordinary  precautions  for  the 
preservation  of  health,  and  hereditary  tendencies  to  various  kinds  of 
morbid  action,  being  too  frequently  the  means  of  cutting  off  the  term  of 
Human  existencOj  long  before  its  natural  expiration. 

4.  Disordered  Conditions  of  the  Nutritive  Processes. 

631.  Having  thus  passed  in  review  the  general  conditions,  under 
which  the  ordinary  Nutritive  processes  take  place,  it  may  be  well  to 
add  a  few  words  in  relation  to  two  of  their  abnormal  states ;  one  or 
other  of  which  is  concerned  in  a  very  large  proportion  of  the  diseases 
that  afflict  the  human  race.  In  one  of  these,  there  is  a  tendency  to  the 
excessive  production  of  fibrine  in  the  blood ;  whilst  in  the  other,  there 
is  a  want  of  the  proper  nutritive  power  in  the  tissues,  which  is  appa- 
rently due  to  an  imperfect  elaboration  of  that  important  material.  The 
one  of  these  conditions  is  termed  Inflammation  ;  whilst  the  other,  which 
is  less  active,  but  more  insidious,  is  known  as  the  Tubercular  Diathesis, 

632.  The  extraordinary  tendency  to  the  production  of  Fibrine  in  the 
blood,  which  has  been  already  noticed  (§  531)  as  one  of  the  most  im- 
portant characters  of  Inflammation,  seems  to  be  always  conjoined  with 
a  depressed  vitality  of  the  tissues  of  some  part  of  the  body,  which  indis- 
poses them  to  the  performance  of  their  regular  nutritive  operations  ;  and 
this  part  may  undergo  a  variety  of  changes,  according  to  the  degree  in 
which  it  is  affected.  The  depressed  condition  of  its  nutritive  operations 
involves,  on  the  principles  explained  in  the  preceding  chapter,  a  languor 
in  the  movement  of  blood  through  it,  together  with  a  distensible  state 
of  the  capillaries,  which  causes  them  to  contain  a  far  greater  amount  of 
that  fluid  than  under  ordinary  circumstances.  On  the  other  hand,  there 
is  a  tendency  to  the  production  of  an  increased  amount  of  plastic  mate- 
rial in  the  blood,  as  if  for  the  reparation  of  the  part  whose  vitality  is 
lowered.  What  is  the  immediate  cause  of  this  production  is  still  doubt- 
ful ;  but  we  see  the  consequences  of  the  deficiency  of  it  in  those  asthenic 
or  unhealthy  Inflammations,  which  so  frequently  involve  the  destruction 
of  a  large  amount  of  tissue ;  the  degeneration  of  the  part  first  affected 
soon  extending  itself  to  others,  if  there  be  no  limit  set  up  by  the  repara- 
tive powers  of  the  blood. — In  ordinary  or  sthenic  Inflammation,  of  which 
the  increase  of  fibrine  in  the  blood,  and  a  diminution  in  the  power  of 
appropriating  it  on  the  part  of  the  tissues,  are  the  most  characteristic 


suppuration;  ulceration;  gangrene.  353 

phenomena,  the  simplest  result  is  the  eflfusion  of  fibrinous  matter,  or 
organizable  lymph,  into  the  substance  of  the  part  inflamed,  or  upon  the 
nearest  free  surface  ;  and  thus  is  produced  a  condensation  of  the  tissue, 
or  a  new  growth  upon  the  membrane.  But  when  the  depression  of 
vitality  is  more  complete,  the  tissue  at  that  spot  gradually  dies  and  dis- 
integrates ;  and  whilst  itself  undergoing  such  changes,  it  gives  origin  to 
similar  changes  in  the  efi'used  fibrine,  which  it.  converts  from  a  plastic 
or  organizable  deposit,  into  an  aplastic  or  unorganizable  one,  namely, 
pus,  the  cells  of  which  degenerate  without  passing  into  any  higher  or 
more  permanent  form  of  tissue,  whilst  the  liquid  through  which  they 
are  dispersed  has  lost  its  coagulating  power.  Thus  is  produced  the 
Suppurating  process  ;  which  may  either  take  place  in  a  cavity  thus  ex- 
cavated in  the  .substance  of  a  tissue  or  organ ;  or  on  a  free  surface.  In 
either  case,  the  surrounding  tissues,  which  are  less  inflamed,  and  in 
which  the  vitality  is  impaired  but  not  destroyed,  become  consolidated 
by  a  deposition  of  organizable  fibrine,  which  prevents  the  infiltration  of 
pus  through  their  substance.  If  this  should  not  occur,  through  a  want 
of  power  to  generate  well-elaborated  fibrine,  the  suppurating  process 
extends  itself  rapidly,  with  the  most  calamitous  results ;  the  properties 
of  pus  being  such,  as  to  produce  a  tendency  to  decomposition,  both  in 
the  bloo4,  and  in  the  solid  tissues  into  the  substance  of  which  it  may  be 
carried. 

633.  Another  consequence  of  Inflammation  is  Ulceration,  which  is 
a  breach  of  surface  caused  by  the  same  process  as  that  which  forms 
the  cavity  of  an  abscess, — namely,  the  degeneration  of  the  inflamed 
tissue,  and  the  removal  of  its  particles,  either  by  absorption,  or  by 
solution  and  ejection  in  pus.  Many  ulcers  commence  as  abscesses  near 
the  surface,  which  at  last  come  to  open  upon  it ;  and  others  are  pre- 
ceded by  inflammation  of  the  superficial  tissues,  which  die  and  are 
thrown  off,  leaving  a  vacuity,  which  may  be  subsequently  increased  by 
the  extension  of  the  degeneration  to  the  deeper  parts.  These  may 
either  die  and  be  thrown  off  en  masse,  constituting  what  is  known  as 
the  "sloughing  ulcer,"  or  they  may  disintegrate  more  slowly,  and  may 
be  dissolved  in  the  discharge  from  the  ulcerated  surface.  This  dis- 
charge, when  proceeding  from  a  spreading  ulcer,  is  usually  of  a  thin 
ichorous  quality,  and  has  the  power  of  exciting  unhealthy  action  even 
in  healthy  parts  to  which  it  may  be  applied ;  and  it  is  its  change  to 
what  has  been  designated  as  "laudable  pus,"  that  indicates  the  cessa- 
tion of  the  destructive,  and  the  commencement  of  the  reparative  pro- 
cess (§  636). 

634.  The  state  of  Crangrene,  which  consists  in  the  entire  loss  of 
vitality  of  the  part,  with  a  complete  cessation  of  the  circulation  through 
it,  is  commonly  regarded  as  a  result  of  Inflammation,  when  this  process 
occurs  in  its  most  intense  form ;  but  it  may  be  more  rightly  considered 
as  the  ultimate  consequence  of  the  causes  which  produce  Inflammation. 
For  it  is  an  essential  part,  as  we  have  seen,  of  the  condition  of  Inflam- 
mation, that  the  vitality  of  the  affected  tissues  should  be  lowered ;  and 
thus  there  is  in  them  always  a  tendency  to  death,  which  is  most  com- 
pletely developed  in  Gangrene.  We  have  a  well-marked  example  of 
this  complete  destruction  of  the  life  of  a  part,  by  the  intense  operation 

.23 


354  OP  NUTRITION. 

of  causes,  which,  when  less  potent,  occasion  Inflammation,  in  the  case 
of  frost-bites  produced  by  Cold ;  for  this  agent  at  the  same  time  pro- 
duces contraction  of  the  blood-vessels,  and  depression  of  the  vital 
powers  of  the  solid  tissues,  proceeding  to  the  complete  destruction  of 
them;  whilst  in  the  parts  adjoining  those  which  are  actually  killed,  the 
inflammatory  state  is  developed,  an  efiusion  of  fibrine  being  produced, 
which  serves  to  plug  up  the  mouths  of  the  vessels,  and  thus  to  prevent 
hemorrhage,  when  the  mortified  part  drops  off.  Here  we  see,  that  the 
violent  action  of  cold  completely  destroys  the  vitality  of  the  part  most 
exposed  to  it;  and  this  by  its  direct  influence  on  the  properties  of  the 
organized  structure.  No  inflammation  can  take  place  in  the  part  thus 
killed,  because  the  vital  processes  are  altogether  brought  to  an  end. 
But  inflammation  takes  place  in  the  adjoining  parts,  which  are  less 
seriously  affected ;  for  the  depression  of  their  vital  powers  occasions 
the  result  already  adverted  to, — namely,  the  production  of  an  increased 
amount  of  fibrine  in  the  blood,  and  an  infiltration  of  this  substance 
into  their  tissues.  The  same  is  the  case,  with  regard  to  the  operation 
of  other  powerful  agents ;  such  as  those  which  (like  Caustic  Potass,  or 
Sulphuric  Acid)  destroy  the  vitality  of  the  parts  to  which  they  are 
applied,  by  the  chemical  decomposition  of  their  tissues.  The  Inflam- 
matory process  is  set  up,  not  in  the  parts  which  are  killed  by  the  appli- 
cation, but  in  the  surrounding  tissues,  whose  vitality  has  been  simply 
depressed ;  and  thus,  when  the  slough,  or  dead  part,  is  cast  off,  there  is 
a  preparation  for  the  development  of  new  tissue  to  supply  its  place, 
from  the  superabundant  plastic  materials  of  the  surrounding  parts. 

635.  If,  then,  we  limit  the  term  Inflammation,  as  there  seems  reason 
to  do,  to  that  state,  in  which  there  is  a  tendency  to  stagnated  circula- 
tion, with  increased  production  of  Fibrine,  in  the  vessels  of  the  part, 
we  see  that  Gangrene  cannot  be  a  result  of  that  process,  which  is  one 
rather  of  reparation  than  of  destruction.  But  Gangrene  proceeds, 
where  we  can  distinctly  trace  its  causes,  from  the  violent  operation  of 
the  same  agents,  as  those  which,  in  a  less  degree,  produce  Inflammation. 
And  where  this  last  process  is  not  set  up  at  the  line  of  demarcation 
between  the  living  and  the  dead  parts.  Gangrene,  like  Suppuration,  has 
a  tendency  to  spread ;  the  influence  of  the  decay,  which  is  taking  place 
in  one  part,  having  a  tendency  to  propagate  itself,  to  the  adjoining 
tissues  ;  and  a  constantly-extending  destruction  being  thus  produced. 

636.  We  have  now  to  speak  of  those  reparative  processes,  by  which 
the  effects  of  disease  or  injuries  are  more  or  less  perfectly  recovered 
from. — The  healing  of  a  simple  wound  may  take  place  by  the  direct 
adhesion  of  its  walls,  when  they  can  be  drawn  closely  together ;  but 
more  frequently  it  is  accomplished  by  the  intermediation  of  a  thin 
layer  of  "coagulable  lymph,"  which  may  be  thrown  out  for  the  purpose 
of  reparation,  without  the  existence  of  inflammatory  action.  But  the 
reparation  of  wounds,  in  which  there  has  been  so  great  a  loss  of  sub- 
stance that  neither  direct  nor  indirect  adhesion  can  take  place,  is 
accomplished  by  the  gradual  development  of  new  tissue  from  the 
"nucleated  blastema"  with  which  the  cavity  is  first  filled.  This, 
however,  may  occur  in  two  very  different  modes ;  and  from  the  inqui- 
ries of  Mr.  Paget  it  appears  that  the  determination  of  one  or  the  other 


REPARATIVE  PROCESS — GRANULATION.  355 

of  them  is  chiefly  dependent  on  the  condition  of  the  wound,  as  to  seclu- 
sion from  air,  or  exposure  to  it.  When  the  reparative  effusion  is 
poured  out  into  a  subcutaneous  wound,  the  "nucleated  blastema" 
appears  to  be  gradually  developed  into  fibrous  tissue  without  any  loss, 
and  usually  with  freedom  from  local  inflammation  (beyond  what  may 
be  the  immediate  result  of  the  injury),  as  well  as  from  constitutional 
irritation.  This  process  seems  to  take  place  naturally  in  cold-blooded 
animals,  even  in  superficial  wounds ;  the  contact  of  air  not  producing 
that  disturbance  in  it,  which  it  occasions  in  warm-blooded  animals. 
And  Nature  frequently  endeavours  (so  to  speak)  to  bring  it  about  in 
the  superficial  wounds  of  warm-blooded  animals,  by  the  formation  of  a 
large  scab,  which  protects  the  exposed  surface ;  but  this  happens  much 
less  frequently  in  the  Human  subject,  than  it  does  among  the  lower 
animals ;  the  unnatural  conditions  in  which  a  large  proportion  of  the 
more  civilized  races  habitually  live  (especially  deficient  purity  of  the 
air,  continual  excess  in  diet,  and  the  frequent  abuse  of  stimulants), 
being  obviously  unfavourable  to  it.  The  application  of  steam  to 
wounded  surfaces  has  been  found  to  favour  the  reparation  by  the  most 
healthy  process ;  and  the  formation  of  an  artificial  scab  by  means  of 
resinous  unguents  has  also  been  practised  with  advantage.  It  is  the 
duty  of  the  Surgeon  to  endeavour  to  promote  it  by  every  means  in  his 
power ;  since  it  is  the  method  of  healing,  which  is  not  merely  the  most 
desirable  as  regards  its  economy  of  nutritive  material  and  freedom 
from  constitutional  irritation,  but  which  most  completely  supplies  the 
loss  of  substance,  so  that  the  cicatrix  does  not  contract.  The  newly- 
formed  fibrous  tissue  becomes  vascular,  by  the  extension  of  loops  or 
arches  from  the  adjacent  capillaries,  and  of  other  loops  from  these; 
and  subsequently  other  structures — such  as  bone,  lymphatics,  and 
nerves, — may  be  developed  in  it.  True  Cartilaginous  tissue,  and  the 
higher  form  of  Muscular  fibre,  however,  seem  never  to  be  thus  generated 
de  novo  in  the  new  tissues  of  a  repaired  part ;  so  that  wounds  of  Carti- 
lages and  Muscles  are  united  by  simple  fibrous  texture. 

637.  In  an  open  wound,  on  the  other  hand,  which  is  healing  by  the 
process  termed  Crranulation,  the  "nucleated  blastema"  is  rapidly  deve- 
loped into  cells,  amongst  which  vessels  speedily  extend  themselves ;  but 
the  vitality  of  this  tissue  is  very  low,  and  that  part  of  it  which  is  ex- 
posed to  the  air  passes  into  the  condition  of  pus^  its  cells  being  either 
imperfectly  developed  from  the  first,  or  speedily  undergoing  degenera- 
tion. Thus  there  is  a  constant  waste  of  plastic  material,  the  amount  of 
which,  in  the  case  of  an  extensive  suppurating  sore,  must  be  a  serious 
drain  upon  the  system ;  whilst  at  the  same  time,  the  local  inflammation 
is  greater,  and  gives  rise  to  more  or  less  of  constitutional  disturbance ; 
and  the  formation  of  new  tissue  is  so  much  less  complete,  that  by  its 
subsequent  degeneration,  and  removal  by  absorption,  a  contracted  cica- 
trix is  produced,  which  is  different  from  the  original  texture.  The  new 
tissue  is  here  produced  by  a  metamorphosis  of  cells  into  fibres ;  and  this 
change  is  taking  place  in  the  deeper  part  of  the  granulation-structure, 
whilst  the  more  superficial  is  degenerating  into  pus. — The  difference 
between  the  two  modes  of  reparation  now  described,  is  often  one  of  life 
and  death,  especially  in  the  case  of  large  burns  of  the  trunk  in  children; 


356  OF  NUTKITION, 


for  it  frequently  happens  that  the  patient  sinks  under  the  great  const 
tutional  disturbance  occasioned  by  a  large  suppurating  surface,  although 
he  may  have  survived  the  immediate  shock  of  the  injury. 

638.  If  the  Fibrine  of  the  Blood,  however,  be  not  well  elaborated,  it 
does  not  possess  its  due  organizability ;  and  thus,  instead  of  being  con- 
verted, either  when  effused  as  an  Inflammatory  product,  or  in  the  ordi- 
nary Nutritive  process  into  solid  tissue,  proper  to  the  part  in  which  it 
is  deposited,  it  is  liberated  from  the  vessels  in  a  state,  which  prevents 
any  but  a  very  imperfect  structure  from  being  developed  by  it,  and 
which  tends  to  very  speedy  degeneration.  This  is  the  condition  of  the 
Tubercular  substance,  which  is  so  often  found  to  replace  the  proper 
tissue,  especially  in  the  lungs ;  being  slowly  deposited  there,  by  a  sort 
of  degradation  of  the  regular  nutritive  operations ;  and  being  effused  in 
larger  quantity,  when  the  inflammatory  process  is  set  up.  There  is 
every  degree  of  gradation  between  the  plastic  or  organizable  deposit  of 
well-elaborated  Fibrine,  the  caco-plastic  or  imperfectly -organizable  mat- 
ter of  Tubercle,  and  the  aplastic  or  non-organizable  matter  of  Pus.  The 
microscopic  examination  of  tubercular  deposits  shows,  that  they  some^ 
times  contain  fully-developed  cells  and  fibres,  analogous  to  those  of 
fibrinous  exudations ;  but  that  more  frequently,  the  cells  and  fibres  are 
imperfectly  formed,  and  are  accompanied  by  a  large  quantity  of  a  gra- 
nular substance,  which  strongly  resembles  coagulated  Albumen ;  and 
that  in  many  cases,  there  is  scarcely  any  trace  of  organization  in  the 
mass.  The  greatest  degree  of  organization  is  found  in  the  semi-trans- 
parent, miliary,  gray,  and  tough  yellow  forms  of  Tubercle  ;  the  least  in 
the  opaque,  crude,  or  yellow  Tubercle. — It  is  the  opinion  of  some  emi- 
nent Pathologists,  that  Tubercular  matter  is  always  deposited  in  the 
first  instance  in  the  cellular  form ;  but  that  it  tends  to  undergo  a  rapid 
and  complete  degeneration. 

639.  The  constitutional  state,  which  predisposes  to  this  perversion 
of  the  ordinary  nutritive  operations,  and  which  is  known  as  the  Tuber- 
cular Diathesis,  may  be  the  result  of  the  continued  operation  of  any 
causes,  that  tend  to  depress  the  vital  powers ;  such  as  insufficient  nutri- 
tion, habitual  exposure  to  cold  and  damp,  protracted  mental  depression, 
&c. ;  or  it  may  be  derived  from  the  operation  of  the  same  or  other 
causes  on  the  ancestors  of  the  individual,  being  one  of  those  disorders 
which  has  a  peculiar  tendency  to  become  hereditary.  The  treatment 
must  be  directed  to  the  invigoration  of  the  system  by  good  food,  active 
exercise,  pure  air,  warm  clothing,  and  cheerful  occupations ;  and  by  the 
due  employment  of  those  means,  at  a  sufficiently  early  period,  many 
valuable  lives  may  be  saved,  which  would  otherwise  fall  a  sacrifice  to 
Tubercular  disease  in  the  lungs,  or  other  important  organs.^Much 
reason  has  lately  presented  itself  for  the  belief,  that  a  deficiency  of 
appropriate  oleaginous  constituents  in  the  food  exerts  a  marked  influ- 
ence in  the  production  of  the  Tubercular  diathesis.  This  would  appear 
to  be  indicated  by  the  very  marked  benefit  which  has  been  derived  in 
the  treatment  of  Pulmonary  Consumption  and  other  tubercular  diseases, 
from  the  use  of  Cod-liver  oil,  or  of  other  easily  assimilated  fish-oils. 
And  the  same  view  is  confirmed  by  the  remarkable  exemption  of  the 
Icelanders  (whose  diet  is  extremely  oleaginous)  from  Tubercular  dis- 


I 


NATURE  AND   CONDITIONS   OF   THE   RESPIRATORY  PROCESS.       357 

eases,  notwithstanding  that  the  general  habits  of  the  people  would  seem 
peculiarly  favourable  to  their  production. 

640.  There  is  another  remarkable  class  of  diseases,  resulting  from  a 
disordered  condition  of  the  nutritive  processes ; — those,  namely  of  % 
malignant  nature.  We  not  unfrequently  meet  with  abnormal  growths 
of  a  fatty,  cartilaginous,  fibrous,  or  bony  structure ;  which  appear  to 
originate  in  some  perverted  action  of  the  part  itself,  and  which  have 
little  tendency  to  reappear  in  the  same  part,  when  they  have  been 
removed,  still  less,  to  reappear  in  distant  parts.  But  the  various 
forms  of  Malignant  or  Cancerous  disease  are  peculiar  in  this, — that 
they  are  composed  of  cells,  sometimes  of  a  globular  form  (see  Fig.  18), 
sometimes  elongated  or  spindle-shaped,  having  a  power  of  rapid  multi- 
plication, and  not  capable  of  changing  into  any  kind  of  normal  tissue. 
When  a  truly  cancerous  growth  has  once  established  itself  in  any  part 
of  the  body,  it  may  increase  to  an  unlimited  extent,  obtaining  its 
nourishment  from  the  blood-vessels  in  its  neighbourhood,  and  destroy- 
ing the  surrounding  parts  by  its  pressure,  as  well  as  by  drawing-off 
their  supply  of  aliment.  When  it  has  developed  itself  to  a  consi- 
derable degree  in  one  part,  it  is  very  liable  to  make  its  appearance 
in  others,  especially  when  the  original  growth  has  been  removed ;  and 
hence  the  judicious  surgeon  is  disinclined  to  remove  a  Cancerous 
growth  of  any  but  the  most  limited  kind ;  knowing  that  the  disease  is 
almost  certain  to  reappear.  There  is  a  strong  analogy  between  such 
Cancerous  growths,  and  the  low  forms  of  Fungoid  Vegetation,  which 
develope  themselves  in  the  interior  of  the  higher  Plants,  and  even  in 
Animal  bodies  ;  and  in  both  cases,  the  disease  may  be  propagated  by 
inoculation  from  one  individual  to  another.  But  still  it  appears  pro- 
bable that  Cancerous  disease,  like  tubercular,  is  of  constitutional  origin; 
and  the  peculiar  tissue  which  characterizes  it,  is  perhaps  to  be  regarded 
simply  as  the  manifestation  of  the  presence  of  a  morbid  matter  in  the 
blood,  which  is  thus  removed  from  the  circulating  current ;  just  as  fatty 
matter  is  removed  by  an  increased  formation  of  Adipose  tissue,  or  as 
the  elements  of  the  excretions  are  eliminated  by  an  increased  growth  of 
the  gland- cells  of  which  they  are  the  appropriate  pabulum. 


CHAPTER  YIIL 

OF  RESPIRATION. 

1.  Essential  Nature  and  Conditions  of  the  Respiratory  Process. 

641.  The  function  of  Respiration  essentially  consists  in  an  inter- 
change of  oxygen  and  carbonic  acid,  between  the  blood  of  the  Animal 
and  the  surrounding  medium ;  carbonic  acid  being  given  out  by  the 
blood,  and  oxygen  entering  in  its  stead.  It  has  been  already  noticed 
(§  84)  that  this  function  is  performed  likewise  by  Plants  ;  although, 
in  consequence  of  their  deriving  a  large  part  of  their  food  from  the 


358  OP  RESPIRATION. 

atmosphere  by  a  converse  process — the  absorption  of  carbon  and  the 
liberation  of  oxygen, — their  true  respiration  is  commonly  overlooked. 
It  may,  therefore,  be  regarded  as  common  to  all  Organized  beings. 
Every  one  is  conscious,  in  his  own  person,  of  the  imperative  demand 
for  the  due  performance  of  this  operation.  If  the  breath  be  purposely 
held  for  even  a  few  seconds,  a  feeling  of  distress  is  experienced,  which 
increases  every  moment,  and  at  last  prompts  irresistibly  to  the  respi- 
ratory movement.  And  if  the  admission  of  air  to  the  lungs  be  in  any 
way  prevented,  the  respiratory  movements  are  at  first  increased  in 
energy,  violent  efforts  are  made  to  obtain  the  needed  supply;  these 
are  succeeded  by  irregular  convulsive  actions,  and  at  the  same  time 
insensibility  comes  on ;  and  within  a  short  time  all  movement  ceases, 
the  circulation  of  the  blood  is  suspended,  and  a  stop  is  put  to  all  the 
vital  operations  of  the  body.  This  state,  which  is  termed  Asphyxia, 
usually  comes  on,  in  a  warm-blooded  animal,  within  ten  minutes  of 
the  time  when  the  respiration  is  completely  checked ;  thus  affording  the 
most  convincing  proof  of  the  importance  of  that  function  in  the  Animal 
economy.  In  many  cold-blooded  tribes,  however,  a  much  longer  sus- 
pension may  be  borne  with  impunity;  as  also  by  warm-blooded  animals, 
when  the  general  activity  of  their  functions  is  lowered  in  the  state  of 
hyhernation  (§  121).  We  shall  now  inquire  into  the  sources  of  the 
necessity  for  this  interchange  of  oxygen  and  carbonic  acid ;  and  the 
mode  in  which  the  suspension  of  it  acts  upon  the  system  at  large. 

642.^  All  Organized  bodies,  as  already  explained,  are  liable  to  con- 
tinual decay^  even  whilst  they  are  most  actively  engaged  in  performing 
the  actions  of  Life ;  and  one  of  the  chief  products  of  that  decay  is  car- 
bonic acid.  A  large  quantity  of  this  gas  is  set  free,  during  the  decom- 
position of  almost  every  kind  of  organized  matter ;  the  carbon  of  the 
substance  being  united  with  oxygen  supplied  by  the  air.  Hence  we 
find,  that  the  formation  and  liberation  of  carbonic  acid  goes  on  with 
great  rapidity  after  death,  both  in  the  Plant  and  in  the  Animal ;  and 
that  it  takes  place  also,  to  a  very  great  extent,  in  the  period  that  often 
precedes  the  death  of  the  body,  during  which  a  general  decomposition 
of  the  tissues  is  going  on.  Thus  in  Plants,  as  soon  as  they  become 
unhealthy,  the  extrication  of  carbon  in  the  form  of  carbonic  acid  takes 
place  in  greater  amount,  than  its  fixation  from  the  carbonic  acid  of  the 
atmosphere ;  and  the  same  change  normally  takes  place  during  the 
period  that  immediately  precedes  the  annual  fall  of  the  leaves,  their 
tissue  being  no  longer  able  to  perform  its  proper  functions,  and  giving 
rise  by  its  incipient  decay,  to  a  large  increase  in  the  quantity  of  car- 
bonic acid  set  free.  The  same  thing  probably  happens  in  the  Animal 
body,  during  the  progress  of  many  diseases  which  are  attended  with  an 
extraordinary  tendency  to  decomposition  in  the  solids  and  fluids ;  for  in 
such  cases  the  blood  usually  exhibits  an  unusually  dark  hue,  indicating 
that  it  has  not  been  properly  freed  from  the  unusual  amount  of  carbonic 
acid  which  it  has  received  from  the  tissues.  It  has  not  yet  been  accu- 
rately determined,  however,  whether  there  is  an  increase  in  the  amount 
of  carbonic  acid  actually  thrown  off  in  s)ich  cases. 

643.  Hence,  the  first  object  of  the  Respiratory  process,  which  is 
coijimon  to  all  forms  of  Organized  being,  is  to  extricate  from  the  body 


SOURCES   OP  EXCRETION   OF  CARBONIC  ACID.  359 

the  carbonic  acid,  which  is  one  of  the  products  of  the  continual  decom- 
position of  its  tissues. "  The  softness  of  many  of  the  tissues  of  Animals, 
and  the  large  quantity  of  fluid  contained  in  their  bodies,  render  them 
more  prone  than  Plants  to  this  kind  of  decomposition ;  and,  in  warm- 
blooded animals,  the  high  temperature  at  which  the  fabric  is  usually 
maintained,  adds  considerably  to  the  degree  of  this  tendency;  so  that 
the  waste  of  their  tissues,  from  this  cause  alone,  is  as  much  greater 
than  that  of  cold-blooded  animals,  as  the  latter  is  than  that  of  Plants. 
But  when  the  temperature  of  the  Reptile  is  raised  by  external  heat  to 
the  level  of  that  of  the  Mammal,  its  need  for  respiration  increases,  owing 
to  the  augmented  waste  of  the  tissues.  When,  on  the  other  hand,  the 
warm-blooded  Mammal  is  reduced,  in  the  state  of  hybernation,  to  the 
level  of  the  cold-blooded  Reptile,  the  waste  of  its  tissues  diminishes  to 
such  an  extent,  as  to  require  but  a  very  small  exertion  of  the  respiratory 
process  to  get  rid  of  the  carbonic  acid,  which  is  one  of  its  chief  products. 
And  in  those  animals  which  are  capable  of  retaining  their  vitality  when 
frozen  (§  136),  or  when  their  tissues  are  completely  dried  up  (§  159), 
the  decomposition  is  for  the  time  entirely  suspended,  and  consequently 
there  is  no  carbonic  acid  to  be  set  free. 

644.  But  another  source  of  Carbonic  acid  to  be  set  free  by  the 
Respiratory  process,  and  one  which  is  peculiar  to  Animals,  consists  in 
the  rapid  changes  which  take  place  in  the  Muscular  and  Nervous 
tissues,  during  the  period  of  their  activity.  It  has  been  already  shown 
(§  361),  that  there  is  strong  reason  to  believe  the  waste  or  decomposi- 
tion of  the  Muscular  tissue  to  be  in  exact  proportion  to  the  degree  in 
which  it  is  exerted  ;  every  development  of  muscular  force  being  accom- 
panied by  a  change  in  the  condition  of  a  certain  amount  of  tissue.  In 
order  that  this  change  may  take  place,  the  presence  of  Oxygen  is 
essential ;  and  one  of  the  products  of  the  union  .of  oxygen  with  the 
elements  of  muscular  fibre,  is  carbonic  acid.  The  same  may  probably 
be  said  of  the  Nervous  tissue  (§  384).  Hence  it  may  be  stated  as  a 
general  principle,  that  the  peculiar  waste  of  the  Muscular  and  Nervous 
substances,  which  is  a  condition  of  their  functional  activity,  and  which 
is  altogether  distinct  from  the  general  slow  decay  that  is  common  to 
these  tissues  with  others,  is  another  source  of  the  carbonic  acid  which 
is  set  free  from  the  animal  body  :  and  that  the  amount  thus  generated 
will  consequently  depend  upon  the  degree,  in  which  these  tissues  are 
exercised.  In  animals  which  are  chiefly  made  up  of  the  organs  of 
vegetative  life,  in  whose  bodies  the  nervous  and  muscular  tissues  form 
but  a  very  small  part,  and  in  whose  tranquil  plant-like  existence 
there  is  but  very  little  demand  upon  the  exercise  of  these  structures, 
the  quantity  of  carbonic  acid  thus  liberated  will  be  extremely  small. 
On  the  other  hand,  in  animals,  whose  bodies  are  chiefly  composed  of 
muscle,  and  whose  life  is  an  almost  ceaseless  round  of  exertion,  the 
quantity  of  carbonic  acid  thus  liberated  is  very  considerable. 

645.  We  are  enabled  to  trace  the  connexion  between  the  amount 
of  muscular  exertion,  and  the  quantity  of  carbonic  acid  spet  free  in  the 
act  of  respiration,  in  the  class  of  Insects,  better  than  in  any  other. 
They  have  no  fixed  temperature  to  maintain  ;  and  they  are  consequently 
not  in  the  condition  of  warm-blooded  animals,  in  which  the  quantity  of 


360  OF  RESPIRATION. 

carbonic  acid  set  free  is  kept  up  to  a  more  regular  standard  by  the 
provision  to  be  presently  noticed.  On  the  other  hand,  they  are  pre- 
eminent among  all  Animals,  in  regard  to  the  energy  of  their  muscular 
power  in  relation  to  the  bulk  of  their  bodies ;  and  the  waste  of  muscu- 
lar tissue  during  their  state  of  activity  must  therefore  be  very  great. 
Thus  a  Humble  Bee  has  been  found  to  produce  one-third  of  a  cubic 
inch  of  carbonic  acid  in  the  course  of  a  single  hour,  during  which  its 
whole  body  was  in  a  state  of  constant  movement,  from  the  excitement 
consequent  upon  its  capture :  and  yet  during  the  whole  twenty-four  hours 
of  the  succeeding  day,  which  it  passed  in  a  state  of  comparative  rest, 
the  quantity  of  carbonic  acid  generated  by  it  was  absolutely  less. 

646.  Besides  these  sources  of  Carbonic  acid,  which  are  common  to 
all  animals,  there  is  another,  which  appears  to  be  peculiar  to  the  two 
highest  classes,  Birds  and  Mammals.  These  are  capable  of  maintain- 
ing a  constantly-elevated  temperature,  so  long  as  they  are  supplied 
with  a  proper  amount  of  appropriate  food ;  and  their  power  of  doing  so 
appears  to  depend  upon  the  direct  combination  of  certain  elements  of 
the  food,  with  the  oxygen  of  the  air,  by  a  process  analogous  to  com- 
bustion ;  these  elements  having  been  introduced  into  the  blood  for  that 
purpose,  but  not  having  formed  a  part  of  any  of  the  solid  tissues  of  the 
body,  unless  they  have  been  deposited  in  the  form  of  fat.  The  nature 
of  these  substances  has  been  already  noticed  (§  430).  It  is  quite 
clear  that  they  cannot  be  applied  in  their  original  form,  to  the  nutri- 
tion of  the  tissues  that  originate  in  proteine-compounds ;  and  it  is  tole- 
rably certain  that,  in  the  ordinary  condition  of  the  body,  they  undergo 
no  such  conversion,  as  would  adapt  them  to  that  purpose.  The  Liver 
seems  to  afford  a  channel,  by  which  some  of  the  fatty  matters  are 
drawn  off  from  the  blood  ;  but  even  these  seem,  in  part  at  least,  to 
be  reabsorbed  (§  725),  and  to  be  thrown  off  by  the  respiratory  process. 

647.  The  quantity  of  Carbonic  acid,  that  is  generated  directly 
from  the  elements  of  the  food,  seems  to  vary  considerably  in  different 
animals,  and  in  different  states  of  the  same  individual.  In  the  Carni- 
vorous tribes,  which  spend  the  greater  part  of  their  time  in  a  state  of 
activity,  it  is  probable  that  the  quantity  which  is  generated  by  the 
waste  or  metamorphosis  of  the  tissues  is  sufficient  for  the  maintenance 
of  the  required  teijiperature, — and  that  little  or  none  of  the  carbonic 
acid  set  free  in  respiration  is  derived  from  the  direct  combustion  of  the 
materials  of  the  food.  But  in  Herbivorous  animals  of  comparatively 
inert  habits,  the  amount  of  metamorphosis  of  the  tissues  is  far  from 
being  sufficient ;  and  a  large  part  of  the  food,  consisting  as  it  does  of 
substances  that  cannot  be  applied  to  the  nutrition  of  the  tissues,  is 
made  to  enter  into  direct  combination  with  the  oxygen  of  the  air,  and 
thus  to  compensate  for  the  deficiency.  In  Man  and  other  animals, 
which  can  sustain  considerable  variations  of  climate,  and  can  adapt 
themselves  to  a  great  diversity  of  habits,  the  quantity  of  carbonic  acid 
formed  by  the  direct  combination  of  the  elements  of  the  food  with  the 
oxygen  of  th^air,  will  differ  extremely  under  different  circumstances. 
It  will  serve  as  the  complement  of  that  which  is  formed  in  other  ways  ; 
so  that  it  will  diminish  with  the  increase,  and  will  increase  with  the 
diminution,  of  muscular  activity.     On  the  other  hand,  it  will  vary  in 


SOURCES   OF   CARBONIC   ACID   IN  THE   ANIMAL   BODY.  361 

accordance  with  the  external  tenperature  ;  increasing  with  its  diminu- 
tion, as  more  heat  must  then  be  generated;  and  diminishing  with  its 
increase. — In  all  cases,  if  a  sufficient  supply  of  food  be  not  furnished, 
the  store  of  fat  is  drawn  upon ;  and  if  this  be  exhausted,  the  animal" 
dies  of  cold  (§  117). 

648.  To  recapitulate,  then ;  the  sources  of  Carbonic  acid  in  the  Ani- 
mal body  are  threefold. — 1.  The  continual  decay  of  the  tissues  ;  which 
is  common  to  all  organized  bodies ;  which  is  diminished  by  cold  and 
dryness,  and  increased  by  warmth  and  moisture  ;  which  takes  place 
with  increased  rapidity  at  the  approach  of  death,  whether  this  affect 
the  body  at  large,  or  only  an  individual  part ;  and  which  goes  on  un- 
checked, when  the  actions  of  nutrition  have  ceased  altogether. — 2.  The 
metamorphosis,  which  is  peculiar  to  the  Nervous  and  Muscular  tissues  ; 
which  is  the  very  condition  of  their  activity  ;  and  which,  therefore, 
bears  a  direct  relation  to  the  degree  in  which  they  are  exerted. — 3. 
The  direct  conversion  of  the  carbon  of  the  food  into  carbonic  acid; 
which  is  peculiar  to  warm-blooded  animals  ;  and  which  seems  to  vary 
in  quantity,  in  accordance  with  the  amount  of  heat  to  be  generated. 

649.  Now  the  function  of  Respiration  has  for  its  object,  not  merely 
to  extricate  the  Carbonic  acid  which  is  generated  in  the  system,  but 
likewise  to  introduce  the  Oxygen  which  is  required  to  form  that  car- 
bonic acid ;  the  proportion  of  oxygen  in  the  tissues,  and  in  the  combus- 
tible materials  of  the  blood,  not  being  sufficient  for  this  purpose. 
Hence  it  is  not  enough,  that  the  carbonic  acid  should  be  removed ;  for 
this  may  be  accomplished  by  causing  an  animal  to  breathe  an  atmo- 
sphere which  contains  no  oxygen.  Any  cold  blooded  animal,  such  as  a 
Frog  or  a  Snail,  may  be  kept  in  hydrogen  or  nitrogen  for  several  hours 
or  even  days  ;  and  will  give  out,  during  that  time,  an  amount  of  car- 
bonic acid  nearly  as  great,  as  if  it  had  been  respiring  atmospheric  air. 
But  the  continued  production  of  carbonic  acid  must  have  a  limit,  occa- 
sioned by  the  want  of  oxygen,  and  death  will  then  supervene. — On 
the  other  hand,  a  supply  of  oxygen  may  be  freely  afforded ;  and  yet 
the  presence  of  even  a  small  amount  of  carbonic  acid  in  the  surround- 
ing atmosphere  (in  addition  to  that  which  is  normally  present  in  it, 
§  81)  will  impede  the  extrication  of  that  substance  from  the  blood; 
and  if  the  excess  be  considerable,  the  carbonic  acid  will  not  be  set  free 
at  all ;  so  that  the  same  injurious  results  follow,  as  if  respiration  were 
altogether  prevented  from  taking  place. 

650.  These  two  actions  are  accomplished  by  the  very  same  act ;  ad- 
vantage being  taken  of  the  property  of  "mutual  diffusion,"  which  is 
common  to  all  gaseous  substances  that  do  not  unite  chemically  with  one 
another.  In  virtue  of  this  property,  Hydrogen,  the  lightest  of  gases, 
and  Carbonic  acid,  one  of  the  heaviest,  when  introduced  into  the  same 
vessel,  will  be  found  in  a  short  time  to  have  uniformly  mixed,  notwith- 
standing the  difference  of  their  specific  gravities,  which  are  as  1  to  22. 
Now  this  intermixture  will  take  place,  when  the  two  gases  are  sepa- 
rated by  a  porous  septum ;  each  gas  passing  towards  the  other,  by  an 
action  resembling  the  Endosmose  and  Exosmose  of  liquids  (§  491). 
And  it  may  also  take  place,  when  one  of  the  gases  is  diffused  through 
a  liquid;   provided  that  the   other  gas  is  likewise  capable  of  being 


362  OF   RESPIRATION, 

absorbed  by  the  liquid.  In  this  manner,  as  already  mentioned,  the 
surface  of  venous  blood,  inclosed  in  a  bladder,  may  be  made  to  exhibit 
the  arterial  hue,  by  suspending  the  bladder  in  an  atmosphere  of 
oxygen ;  for  the  carbonic  acid  of  the  blood,  and  the  surrounding 
oxygen,  will  overcome  by  their  mutual  attraction  the  obstacle  inter- 
posed by  the  bladder ;  and  the  former  will  be  lifted  out,  so  to  speak,  and 
will  be  replaced  by  the  latter.  It  has  been  found  by  experiment,  that 
the  free  carbonic  acid  diffused  through  blood,  may  be  more  completely 
extricated  from  the  liquid,  by  exposing  it  to  hydrogen,  than  by  placing 
it  under  the  vacuum  of  an  air-pump ;  for  in  the  latter  case  there  is 
nothing  to  replace  it,  and  the  attraction  between  the  gas  and  the  liquid 
tends  to  resist  the  exhausting  influence  of  the  vacuum;  whilst  in  the 
former,  the  blood  receives  one  gas  in  exchange  for  the  other,  so  that 
the  whole  force  of  the  tendency  to  mutual  diffusion  is  exercised  in  lift- 
ing out  the  carbonic  acid. 

.  651.  The  immediate  purpose  of  the  organs  of  Respiration,  then, — 
whatever  may  be  the  variety  in  their  form, — is  this :  to  expose  the 
blood  to  the  air,  in  a  state  of  such  minute  division  as  to  present  a  very 
extended  surface,  a  thin  membrane  only  being  interposed  between 
them.  For  this  purpose  we  find  a  certain  organ,  or  set  of  organs,  spe- 
cially set  apart  in  all  the  higher  animals ;  and  this  is  formed  by  a 
prolongation  of  the  general  surface,  either  externally  or  internally, 
according  to  the  mode  in  which  the  respiration  is  accomplished.  Thus 
in  Fishes  and  aquatic  Molluscs,  the  blood  is  aerated  by  exposure,  not 
directly  to  the  atmosphere,  but  to  the  air  which  is  dissolved  in  the 
water  they  inhabit ;  and  the  respiratory  apparatus  is  formed  in  them 
of  an  extension  of  the  external  surface,  at  a  particular  part,  into  innu- 
merable delicate  fringe-like  processes,  the  gills  (Fig.  100) ;  every  divi- 
sion of  which  contains  a  network  of  blood-vessels  (Fig.  104) ;  so  that 

Fig.  iOO. 


Doris  Johnston!,  a  Nudibranchiate  Oasteropod,  showing  the  tuft  of  external  gills. 

the  amount  of  blood  which  is  exposed  to  the  surrounding  medium  at 
any  one  time,  is  collectively  very  great,  although  the  quantity  contained 
in  each  gill-filament  is  very  minute.  On  the  other  hand,  in  all  the  air- 
breathing  Yertebrata,  the  blood  is  exposed  to  the  atmosphere,  through 
the  medium  of  an  internal  membranous  prolongation,  which  is  conti- 
nuous with  the  mucous  membrane  lining  the  mouth  and  nostrils ;  this 
forms  a  pair  of  sacs,  termed  lungs,  communicating  with  the  back  of  the 
mouth  by  means  of  a  tube  called  the  trachea  or  windpipe,  through 
which  air  is  freely  admitted  to  the  cavities  thus  formed  (Fig.  105). 


RESPIRATION   IN   MOLLUSCS.  863 

The  blood  is  minutely  distributed  on  the  walls  of  these  sacs  by  a  close 
network  of  Capillary  vessels  (Fig.  106) ;  and  not  only  on  the  external 
walls,  but  also  on  numerous  partitions  by  which  the  cavities  are  sub- 
divided with  more  or  less  minuteness,  so  as  greatly  to  extend  the  vas- 
cular surface. 

652.  Such  is  the  essential  nature  of  the  Respiratory  apparatus  ;  but 
in  order  that  it  may  be  carried  into  that  vigorous  operation,  which  is 
required  in  the  higher  classes  of  animals,  various  supplementary  arrange- 
ments are  made,  for  the  purpose  of  promoting  the  due  influence  of  the 
air  upon  the  blood.  In  the  first  place,  the  capillary  vessels  of  the  respi- 
ratory surface  are  connected  with  arterial  trunks,  which  issue  immedi- 
ately from  the  heart,  and  which  thus  convey  a  constant  stream  of  blood 
from  that  organ ;  whilst  they  give  origin  to  venous  trunks,  which 
terminate  directly  in  the  heart,  and  which  are  ready  to  convey  back  to 
it  the  blood  that  has  undergone  aeration.  Thus  by  the  energetic  action 
of  the  heart,  and  by  the  force  generated  in  the  capillaries  of  the  lungs 
(§  598),  a  constant  renewal  is  efi'ected  in  the  blood,  which  is  exposed  to 
the  air  through  the  medium  of  these  organs.  On  the  other  hand,  the 
renewal  of  the  blood  would  be  useless,  unless  a^  fresh  supply  of  air  were 
continually  being  introduced,  and  that  which  had  been  vitiated,  by  the 
loss  of  its  oxygen  and  the  admixture  of  carbonic  acid,  were  removed ; 
and  this  is  effected  by  a  series  of  muscular  movements,  which  are  adapted 
for  the  alternate  expulsion  of  the  vitiated  air  from  the  lungs,  and  for 
the  introduction  of  a  fresh  supply  of  pure  air  from  the  atmosphere. 
These  movements  are  kept  up  by  a  certain  part  of  the  nervous  system ; 
but  they  are  not  dependent  upon  any  exertion  of  the  will,  for  they  con- 
tinue during  profound  sleep,  and  in  other  states  in  which  even  conscious- 
ness is  altogether  suspended. 

2.  Different  forms  of  the  Respiratory  Apparatus  in  the  lower  Animals. 

653.  Before  proceeding  to  consider,  in  more  detail,  the  structure  and 
actions  of  the  respiratory  apparatus  in  Man,  we  may  advantageously 
glance  at  the  mode,  in  which  this  function  is  effected  in  the  lower  ani- 
mals.— In  the  lowest  and  simplest,  which  are  inhabitants  of  the  water, 
we  do  not  find  any  special  apparatus  for  the  aeration  of  the  fluids  of  the 
body ;  this  being  accomplished  by  the  exposure  of  them  to  the  surround- 
ing medium,  though  the  thin  integument ;  and  th^  interchange  of  the 
layer  of  water  (holding  air  in  solution)  in  contact  with  the  aerating  sur- 
face, is  effected  either  by  the  general  movements  of  the  body,  or  by  the 
action  of  the  cilia  (§  234)  which  produce  the  currents  necessary  for  this 
purpose.  Not  unfrequently,  the  internal  surfaces — such  as  the  walls  of 
the  stomach  and  of  other  cavities, — seem  as  much  concerned  in  this 
function  as  the  external,  or  even  more  so  ;  these  cavities  being  distended 
with  water  taken  in  through  the  mouth,  and  this  water  being  frequently 
renewed  by  the  ejection  of  that  which  has  been  vitiated,  and  by  the  in- 
troduction of  a  fresh  supply.  This  is  the  case  in  the  Sea  Anemone, 
for  example,  and  in  many  other  polypes ;  and  there  are  certain  higher 
forms  of  the  same  class,  in  which  there  is  a  great  dilatation  of  the 
pharynx,  which  seems  peculiarly  destined  for  the  aeration  of  the  fluids, 


364  OF  RESPIHATION. 

— being  filled  with  water,  and  then  suddenly  emptied  at  tolerably  regular 
intervals. 

654.  In  the  various  classes  of  the  Molluscous  sub-kingdom,  we  find 
the  respiration  provided  for,  by  the  adaptation  of  distinct  organs  for  the 
purpose.  As  most  of  the  animals  of  this'  group  are  inhabitants  of  the 
water,  the  respiration  is  usually  carried  on  by  means  of  gills,  rather  than 
by  any  organ  resembling  a  lung.  The  latter  is  found,  however,  in  a 
few  species ;  such  as  the  Snail,  Slug,  and  other  terrestrial  air-breathing 
Molluscs,  and  usually  consists  of  a  simple  cavity,  situated  in  the  back, 
communicating  directly  with  the  air  through  an  aperture  in  the  skin, 
and  having  its  walls  covered  with  a  minute  network  of  blood-vessels. 
The  form  and  position  of  the  gills  differ  extremely  in  the  several  classes 
of  Molluscous  animals.  In  the  lowest  the  respiratory  surface  is  formed, 
as  in  the  higher  Polypes,  by  a  dilatation  of  the  Pharynx  ;  but  sometimes, 
instead  of  surrounding  a  large  cavity,  it  forms  a  special  riband-like  fold 
of  membrane,  passing  from  one  end  of  it  to  the  other,  on  which  the 
blood  is  minutely  distributed.  In  this  group  of  animals,  there  is  a 
regular  system  of  canals  for  the  conveyance  of  the  blood  ;  but  these,  in 
many  parts  of  the  system*,  and  especially  on  the  respiratory  membrane, 
do  not  seem  to  be  furnished  with  distinct  walls,  and  are  rather  mere 
channels  excavated  in  the  tissues.  And  the  circulation  is  liable  to  a 
continual  change  in  its  direction,  the  blood  being  sometimes  transmitted 
to  the  respiratory  surface  before  it  proceeds  to  the  body,  and  sometimes 
after  it  has  traversed  the  other  tissues  (§  557).  The  water  in  contact 
with  the  respiratory  surface  is  continually  renewed  by  the  action  of  the 
cilia,  with  which  it  is  thickly  covered. 

^^k).  In  certain  of  the  Molluscs,  inhabiting  bivalve  shells,  we  find 
that  the  internal  surface  of  the  mantle  or  skin  that  lines  the  valves,  is 
the  special  organ  of  respiration ;  the  external  water  having  free  access 
to  these  by  the  separation  of  the  skin  along  the  edges  of  the  valve,  so 
that  it  enters  the  cavity  in  which  the  viscera  are  lodged,  and  bathes 
their  exterior.  But  in  most  bivalve  molluscs,  the  internal  surface  of 
the  mantle  is  doubled  (as  it  were)  into  four  riband-like  folds,  which  are 
delicately  fringed  at  their  edges,  and  which  have,  in  fact  the  same 
essential  structure  as  the  gills  of  higher  animals  (§  663).  To  these  the 
blood  is  transmitted,  when  it  has  been  rendered  venous  by  traversing 
the  vessels  of  the  body  generally :  and  in  these  it  is  exposed,  through 
a  surface  which  is  greatly  extended  by  the  minute  division  of  the  fringes, 
to  the  action  of  water  introduced  from  without,  and  constantly  renewed 
by  ciliary  action.  In  many  of  these  animals,  as  in  the  common  Oyster, 
the  two  lobes  of  the  mantle  are  so  completely  separated,  that  the  water 
can  still  enter  freely  between  the  valves,  but  in  general,  they  are  more 
or  less  united,  so  that  the  cavity  in  which  the  gills  lie  is  partially  closed. 
There  is  always  a  provision,  however,  for  the  free  access  of  water  from 
without  by  means  of  two  apertures,  one  for  its  entrance  and  the  other 
for  its  ejection,  and  in  certain  species  which  burrow  deeply  in  sand  or 
mud,  these  apertures  are  furnished  with  long  tubes,  or  siphons,  which 
convey  the  water  from  near  the  entrance  of  the  burrow,  and  carry  it 
thither  again.     In  these  also,  a  continual  flow  of  water  over  the  respi- 


RESPIRATION  IN  WORMS  AND   CRUSTACEA.  365 

ratory  surface  is  maintained  by  the  vibration  of  the  cilia,  with  which 
they  are  clothed. 

656.  The  position  of  the  gills,  in  the  Mollusca  of  higher  organization, 
is  extremely  variable.  Sometimes  they  are  disposed  upon  the  external 
surface  of  the  body,  and  form  delicate  leaf-like  or  pjg  jqi^ 
arborescent  appendages  (Fig.  101) ;  whilst  in  other 
cases  they  are  enclosed  in  a  special  cavity  or  gill- 
chamber,  to  which  water  is  freely  admitted  from 
without;  a  continual  interchange  being  provided 
for,  either  by  ciliary  action,  or  by  muscular  move- 
ments specially  adapted  for  the  purpose.  The 
blood  is  conveyed  to  them,  after  having  become 
venous  in  traversing  the  capillaries  of  the  general 
system,  by  means  of  large  channels  and  sinuses 
excavated  in  the  several  parts  of  the  body  (§  556) ; 
and  after  being  aerated  in  the  gills,  it  returns  to 
the  heart,  to  be  again  conveyed  to  the  system.  In  ceSerform^nTThT'L^'of 
the  Cuttle-fish  tribe,  there  are  supplementary  ^^m^^jphnstom,  separated 
hearts  at  the  origin  of  the  branchial  arteries,  or 

vessels  that  distribute  blood  to  the  gills ;  and  these  have  evidently  for 
their  purpose,  to  render  the  respiratory  circulation  more  energetic,  and 
thus  to  increase  the  aeration  of  the  blood,  in  the  degree  required  for  the 
vigorous  habits  of  these  animals,  which  present  a  remarkable  contrast 
to  the  sluggish,  inert  character  of  the  Mollusca  in  general. — In  these 
classes,  taken  as  a  whole,  the  respiration  is  low  in  its  amount.  The 
blood  contains  no  red  corpuscles,  excepting  perhaps  in  the  highest  class  ; 
and  the  change  in  its  composition,  which  is  effected  by  the  air,  is  con- 
fined, therefore,  to  the  fluid  plasma,  or  liquor  sanguinis.  And  as  it  is 
not  exposed  directly  to  the  air,  except  in  a  few  species,  but  to  the  air 
contained  in  the  water  inhabited  by  the  animals,  this  change  cannot  be 
very  energetically  performed.  But  as  the  life  of  these  animals  is  chiefly 
vegetative, — as  their  movements,  except  in  the  highest  classes,  are  few 
and  feeble, — and  as  they  maintain  no  independent  heat, — there  is  but 
little  need  of  that  interchange,  which  it  is  the  object  of  the  respiratory 
process  to  efi'ect ;  and  these  animals  can  sustain  the  complete  suspension 
of  it  for  a  long  time. 

657.  Among  many  of  the  Articulated  tribes,  the  respiration  is  car- 
ried on  upon  a  similar  plan.  In  some  of  the  lowes't,  such  as  the  Tape- 
worm of  the  intestinal  canal,  there  is  no  special  provision  for  the  aera- 
tion of  the  fluids  ;  the  soft  integument  permitting  the  extrication  of  car- 
bonic acid,  and  imbibition  of  oxygen,  in  the  required  degree.  This  is 
but  very  small,  however;  the  life  of  these  animals  being  almost  purely 
vegetative.  In  the  Marine  Worms,  which  constitute  a  numerous  and 
interesting  group,  endowed  with  considerable  locomotive  powers,  and 
leading  a  life  of  almost  constant  activity,  there  is,  on  the  other  hand,  a 
special  provision  for  this  function ;  the  blood  being  transmitted,  in  the 
course  of  its  circulation,  to  a  series  of  gill-tufts,  which  are  composed  of 
a  delicate  membrane  prolonged  from  the  external  surface  of  the  body, 
and  which  sometimes  have  the  form  of  branching  trees,  and  sometimes 
of  delicate  brushes  made  up  of  a  bundle  of  distinct  filaments.     In  either 


'366  OF  RESPIRATION. 

case,  the  filaments  are  traversed  by  blood-vessels,  and  are  adapted  to 
bring  the  blood  into  close  relation  with  the  surrounding  water ;  and  the 
continual  interchange  of  the  latter  is  provided  for  by  the  restless  move- 
ments of  the  body.  The  tufts  are  sometimes  arranged  along  every  seg- 
ment of  the  body ;  and  their  multiplication  prevents  them  from  indivi- 
dually attaining  any  considerable  size.  In  other  cases,  they  are  disposed 
^at  intervals  ;  and  they  are  then  larger,  being  less  numerous.  Their  most 
beautiful  development  is  where  they  are  present  on  the  head  only,  the 
rest  of  the  body  being  enclosed  in  a  shelly  or  sandy  tube,  as  in  the  Ser- 
pulce  and  Terebellce.  The  gill-tufts  then  frequently  present  the  appear- 
ance of  a  flower,  endowed,  when  alive,  with  the  most  brilliant  and  deli- 
cate hues.  In  many  animals  of  this  group,  there  is  a  small  supplemen- 
tary heart  at  the  base  of  every  one  of  the  vessels  that  distribute  the 
blood  to  the  gills  ;  and  this  is  obviously  designed  to  aid  in  the  respiratory 
circulation,  for  which  the  feeble  action  of  the  dorsal  vessel  would  not 
furnish  sufficient  power  (§  552). 

658.  The  higher  Articulated  classes  are,  for  the  most  part,  adapted 
to  atmospheric  respiration,  on  the  plan  to  be  presently  explained;  but 
there  is  one  class,  that  of  Crustacea,  whose  respiration  is  still  carried 
on  through  the  medium  of  water.  In  the  lowest  forms  of  this  group, 
there  is  no  special  respiratory  apparatus  ;  the  general  surface  being  soft 
enough  to  admit  of  the  required  aeration  of  the  fluids  through  its  own 
substance,  and  the  animal  functions  being  performed  with  so  little 
activity,  that  a  very  small  amount  of  interchange  is  required.  In  the 
higher  orders,  however,  whose  bodies  are  encased  within  a  hard  envelope, 
we  find  external  gills,  like  those  of  many  Molluscs ;  and  these  are 
attached  to  the  most  movable  parts  of  the  body, — one  or  more  pairs  of 
legs  being  in  some  instances  kept  in  constant  agitation,  for  the  purpose 
of  producing  currents  in  the  surrounding  fluid,  that  may  serve  for  the 
aeration  of^the  blood.  In  the  Crab-tribe,  which  constitutes  the  highest 
family  of  this  class,  the  gills  are  themselves  enclosed  within  a  cavity, 
formed  by  a  sort  of  doubling  of  the  hard  integument  of  the  under  side 
of  the  body ;  and  a  constant  stream  of  water  is  maintained  through  this, 
by  means  of  a  peculiar  valve,  situated  in  the  exit  pipe ;  the  continual 
movement  of  the  valve  causing  a  regular  stream  of  water  to  issue  from 
the  gill-chamber,  and  thus  occasioning  the  entrance  of  a  constantly-fresh 
supply.  In  these,  also,  we  find  a  dilatation,  the  walls  of  which  seem  to 
have  contractile  powers,  at  the  commencement  of  each  artery  that  dis- 
tributes the  blood  to  the  gills  ;  and  this  collects  the  venous  blood  from 
the  various  channels,  in  which  it  has  meandered  through  the  body.  It 
is  by  the  enclosure  of  the  gills  within  a  cavity,  and  by  the  consequent 
protection  of  them  from  the  drying  influence  of  the  air  (which  would 
prevent  their  function  from  being  duly  performed),  that  Crabs  and  other 
allied  species  are  enabled  to  live  for  a  considerable  time  out  of  water ; 
and  the  Land-Crabs,  as  they  are  termed,  are  adapted  to  spend  the  greater 
part  of  their  lives  at  a  distance  from  the  sea,  by  means  of  a  special 
glandular  apparatus  within  the  gill-cavity,  which  secretes  a  fluid  that 
preserves  the  surface  of  the  gills  in  the  moist  condition  requisite  for  the 
aeration  of  the  blood  through  its  membrane.     Thus  the  Land-Crabs  are 


RESPIRATION  IN  INSECTS  AND   SPIDERS.  367 

air-breathing  animals  (except  at  certain  seasons,  when  they  frequent 
the  sea-shores),  although  they  breathe  by  gills. 

659.  In  Insects  and  other  proper  air-breathing  Articulata,  however, 
the  character  of  the  respiratory  apparatus  is  very  different.  The  tran- 
sition from  one  form  to  the  other  is  effected  through  such  animals  as  the 
Leech  and  the  Earthworm,  which  seem  able  to  live  almost  equally  well 
in  air  or  water,  and  whose  respiration  appears  to  be  carried  on  chiefly, 
if  not  entirely,  through  the  medium  of  the  external  surface  alone.  These 
animals  are  furnished  with  a  series  of  small  sacs,  disposed  at  regular 
intervals  along  each  side  of  the  body,  and  opening  by  a  row  of  pores, 
which  are  termed  spiracles  or  stigmata  ;  but  these  sacculi  do  not  seem 
to  participate  in  the  respiratory  function,  their  office  being  rather  to 
secrete  a  protective  mucus.  But  in  the  Myriapods,  these  sacculi  are 
respiratory  organs,  and  communicate  more  or  less  freely  with  each  other. 
And  in  Insects,  the  spiracles,  instead  of  forming  the  entrances  to  so 
many  distinct  sacs,  open  into  a  pair  of  large  tubes,  one  of  which  tra- 
verses the  body  on  either  side,  along  its  whole  length.  These  tubes, 
termed  trachece,  have  many  communications  with  each  other  across  the 
body ;  and  they  branch  out  into  innumerable  prolongations,  the  ultimate 
ramifications  of  which  are  distributed  to  every  portion  of  the  system. 
They  occasionally  present  dilatations  of  considerable  size  (Fig.  102,  a)  ; 
especially  in  the  thoracic  region  of  the  body,  in  those  insects  which  are 
endowed  with  great  powers  of  flight.  These  dilatations  or  air-sacs  appear 
destined  to  serve  as  reservoirs  of  air,  during  the  time  that  the  insect  is 
upon  the  wing,  its  spiracles  being  then  partially  closed ;  and  they  may 
also  be  useful  in  diminishing  the  specific  gravity  of  the  body.  The  air- 
tubes  are  prevented  from  having  their  cavity  obliterated  through  the 
pressure  of  the  surrounding  parts,  by  means  of  an  elastic  spiral  fibre ; 
which  winds  round  them,  between  their  outer  and  inner  membrane, 
from  one  extremity  to  the  other  (Fig.  102,  b)  ;  and  which  answers  the 
purpose  of  the  cartilaginous  rings  and  plates,  in  the  trachea  and 
bronchi  of  air-breathing  Vertebrata. 

Fig.  102. 


Respiratory  apparatus  of  insects:— a,  air  vesicles  and  part  of  tracheal  system  of  Scolia  hortorum.    B,  por- 
tion of  OJle  of  the  great  longitudinal  tracheae  of  Oardbus  aurcUus,  with  one  of  its  spiracles. 

660.  In  this  manner,  the  air  that  is  introduced  through  the  spiracles 
is  carried  into  every  part  of  the  body,  and  is  brought  into  immediate 
relation  with  the  tissues  to  be  aerated;  so  that  the  carbonic  acid  which 


ft 


368  OF  KESPIRATION. 

they  set  free  is  communicated  at  once  to  the  atmosphere,  instead  of 
being  taken  up  by  the  blood ;  and  the  oxygen  they  require  is  imbibed 
in  the  same  manner.  And  thuswe  see  how  the  respiration  of  this  inte- 
resting class,  which  is  unequalled  for  its  energy  when  the  body  is  in  a 
state  of  activity,  is  provided  for  without  an  active  circulation  of  blood, 
and  without  the  presence  of  red  corpuscles, — which  elsewhere  seem  to 
be  essential  conditions  of  the  interchange  of  oxygen  and  carbonic  acid 
between  the  air  and  the  tissues,  wherever  this  takes  place  to  any  great 
extent. 

661.  In  the  Spider  tribe,  we  return  to  a  more  concentrated  form  of 
the  respiratory  apparatus  ;  but,  notwithstanding  that  it  is  limited  within 
much  narrower  dimensions  externally,  it  exposes  a  very  large  amount 
of  surface  on  its  interior.  It  consists  of  a  series  of  sacs,  much  less 
numerous  than  in  the  lower  Articulata,  and  not  communicating  with 
each  other.  Their  lining  membrane,  however,  is  doubled  into  a  series 
of  folds,  which  lie  in  proximity  with  each  other,  like  the  leaves  of  a 
book,  and  which  thus  present  a  very  extensive  surface  within  a  very 
small  space.  Over  this  surface  the  blood  is  distributed  in  a  minute 
capillary  network ;  and  thus  it  comes  into  immediate  relation  with  the 
air,  which  is  received  into  the  cavity  through  its  aperture  or  spiracle. 
The  alternate  admission  and  expulsion  of  air  seem  to  be  provided  for, 
as  in  Insects,  by  movements  of  the  body,  which  first  empty  the  cavities 
or  air-tubes  by  compression,  and  then  allow  them  to  be  refilled  by  their 
own  elasticity,  the  pressure  being  relaxed.  The  respiratory  cavities  in  the 
Spider-tribe  have  received  the  name  of  pulmonary  brancJiice,  from  their 
analogy,  on  the  one  hand,  with  the  lungs  of  higher  animals,  and,  on  the 
other,  with  the  branchial  sac  or  gill-cavity  of  the  higher  Crustacea,  the 
gills  in  which  are  formed  by  prolongations  of  the  lining  membrane,  like 
the  leaf-like  folds  in  the  air-cavities  of  the  Spider-tribe. 

662.  The  accompanying  diagram  will  give  an  idea  of  the  relations  of 
these  different  forms  of  the  respiratory  apparatus,  amongst  themselves, 
and  to  that  of  Vertebrata.     Let  the  line  ab  represent  the  general 

Fig.  103. 


Diagram  illustrating  diflFerent  forms  of  the  Respiratory  apparatus  :—a,  simple  leaf-like  gill ;  b,  simple 
respiratory  sac ;  c,  divided  gill ;  d,  divided  sac ;  e,  pulmonary  branchia. 

surface  of  the  animal ;  the  continuations  of  that  line  on  its  upper  side 
being  its  external  prolongations ;  and  those  below,  its  internal  prolon- 
gations or  reflexions.  Now  at  a  is  seen  the  character  of  the  simple 
foliaceous  or  leaf-like  gill,  such  as  is  found  in  the  lower  aquatic  animals ; 
presenting  merely  a  flat  expanded  surface  in  contact  with  the  water, 
over  which  the  blood  may  be  distributed.     At  h  is  shown  a  correspond- 


RESPIRATION  IN  FISHES.  369 

ingly  simple  inversion  ;  such  as  that  which  forms  the  respiratory  sac  of 
the  Leech,  having  the  blood-vessels  distributed  upon  its  walls.  A 
higher  form  of  the  gill,  such  as  is  found  in  Fishes  and  in  the  higher 
aquatic  Invertebrata,  is  seen  at  c,  the  surface  being  greatly  extended, 
by  subdivision  into  minute  filaments.  A  more  complex  form  of  the 
pulmonary  apparatus,  such  as  is  found  in  the  higher  Vertebrata,  is 
shown  at  d,  the  blood  being  distributed,  not  merely  to  its  outer  walls, 
but  to  the  minute  partitions  which  subdivide  its  cavity  into  cells.  And 
at  e  is  represented  the  respiratory  organ  of  the  Spider-tribe,  which 
bears  an  obvious  resemblance  to  the  lung  of  the  Vertebrated  animal, 
shown  at  d;  whilst  it  is  evidently  as  nearly  allied  to  the  gill  shown 
at  c,  provided  this  be  imagined  to  be  sunk  within  a  cavity  formed  by  a 
depression  of  the  external  surface,  instead  of  projecting  beyond  it. — 
Thus  we  see  how  very  close  is  the  real  resemblance  between  all  the 
forms  of  the  respiratory  apparatus,  however  unlike  each  other  they  may 
at  first  sight  appear  to  be. 

663.  The  gills  of  Fishes  correspond  with  those  of  the  higher  MoUusca 
in  all  essential  particulars ;  but  they  are  more  largely  developed  in  pro- 
portion to  the  size  of  the  body ;  and  they  are  placed  in  a  situation,  that 
enables  them  to  receive  a  more  regular  and  constantly-changed  supply, 

Fig.  104. 


^^dp^ 


Capillary  network  of  a  pair  of  leaflets  of  the  gills  of  the  Eel  :—a,  a,  branches  of  the  branchial  artery  con- 
veying venous  blood;  6,  b,  branches  of  the  branchial  vein,  returning  aerated  blood.  The  disappearance  of 
the  dark  shading  in  the  network,  as  it  traverses  the  gill,  is  designed  to  indicate  the  change  in  the  character 
of  the  blood,  as  it  passes  from  one  side  to  the  other. 

both  of  blood  and  water.  The  gills  are  suspended  to  bony  or  cartilagi- 
nous arches,  of  which  three,  four,  or  more,  are  fixed  on  either  side  of 
the  neck ;  and  the  fringes  hang  loosely  within  a  cavity,  which  commu- 
nicates on  the  one  hand  with  the  mouth,  and  on  the  other  with  the  ex- 
terior of  the  body.  The  mechanism  of  respiratioti  is  very  complex  in 
these  animals ;  and  is  evidently  adapted  to  produce  the  most  effectual 
aeration  possible.  The  mouth  is  first  distended  with  water ;  and  its 
muscles  are  then  thrown  into  contraction,  in  such  a  manner  as  to  expel 
the  water,  through  the  aperture  on  either  side  of  the  pharynx,  into  the 
gill-cavity.  At  the  same  time,  the  bony  arches  are  lifted  and  separated 
from  each  other,  by  the  action  of  muscles  especially  adapted  to  this 
purpose  ;  so  that  the  gill-fringes  may  hang  freely,  and  may  present  no 
obstacle  to  the  flow  of  the  water  between  them.  When  they  have  been 
thus  bathed  with  the  aerating  liquid,  and  their  blood  has  undergone  the 
necessary  change,  the  water  is  expelled  through  the  outward  aperture 
on  each  side  of  the  back  of  the  neck ;  which  is  furnished  with  a  large 

Iap  or  valvular  cover,  termed  the  operculum.      In  some  of  the  cartila- 


370  OP  RESPIRATION. 

ginous  Fishes,  each  branchial  arch  is  inclosed  in  a  separate  cavity; 
which  communicates  on  the  inner  side  with  the  pharynx  by  an  orifice 
peculiar  to  itself,  and  by  another  orifice  with  the  external  surface. 
Thus  there  is  a  series  of  external  openings,  instead  of  a  single  one,  on 
each  side  of  the  neck ;  and  these  sometimes  amount  to  six  or  seven,  as 
in  the  Lamprey,  reminding  us  of  the  spiracles  of  Articulated  animals ; 
whilst  there  is  a  corresponding  series  of  internal  openings  into  the  pha- 
rynx on  either  side,  or  into  a  tube  that  communicates  with  it. 

664.  It  is  well  known,  that  most  Fishes  speedily  die  when  removed 
from  the  water ;  and  it  can  be  easily  shown,  that  the  deficient  aeration 
of  the  blood  is  the  immediate  cause  of  their  death.  But  as  it  might 
have  been  expected,  that  the  atmosphere  would  exert  a  much  more 
energetic  influence  upon  the  blood  contained  in  the  gills,  than  that 
which  is  exercised  by  the  air  contained  in  the  water,  the  question 
naturally  arises,  how  this  deficient  aeration  comes  to  pass.  It  is  chiefly 
due  to  the  two  following  causes : — the  drying-up  of  the  membrane  of 
the  gills  themselves,  where  it  is  exposed  to  the  air,  so  that  the  aeration 
of  the  blood  is  impeded ; — and  the  flapping  together  of  the  filaments  of 
the  gills,  which  no  longer  hang  loosely  and  apart,  but  adhere  in  such 
a  manner  as  to  prevent  the  exposure  of  the  greater  portion  of  their 
surface  to  the  air.  Those  fishes  can  live  longest  out  of  water,  in  which 
the  external  gill-openings  are  very  small,  so  that  the  gill-cavity  may 
be  kept  full  of  fluid ;  and  there  are  certain  species  which  are  provided, 
like  the  Land-crab,  with  a  particular  apparatus  for  keeping  the  gills 
moist,  and  which  perform  long  migrations  over  land  in  search  of  food, 
even  (it  is  said)  ascending  trees.  These  are  exceptions  to  the  general 
rule. 

665.  The  respiration  of  Fishes  is  much  more  energetic  than  that  of 
any  of  the  lower  aquatic  animals ;  and  this  is  partly  due  to  the  great 
extension  of  the  surface  of  the  gills,  partly  to  the  provision  just  ex- 
plained for  maintaining  a  constant  flow  of  fresh  water  over  their  sur- 
face, and  partly  to  the  position  of  the  heart  at  the  base  of  the  main 
trunk  that  conveys  the  blood  to  the  gills  {§  658),  by  which  the  regular 
propulsion  of  that  fluid  through  these  organs  is  secured.  Their  blood 
too,  is  furnished  with  red  corpuscles ;  which  give  important  aid  in  con- 
veying oxygen  from  the  gills  to  the  remote  tissues  of  the  body,  and  in 
returning  the  carbonic  acid  to  be  excreted.  The  proportion  of  these 
varies  considerably,  in  the  difierent  species  of  the  class,  being  very 
small  in  those  that  approach  most  nearly  to  the  Invertebrata ;  and  there 
is  even  an  entire  absence  of  them  in  one  remarkable  fish,  the  Amphi- 
oxus  or  Lancelot ;  whilst  they  are  present  in  large  numbers  in  the  blood 
of  certain  Fishes,  which  have  great  muscular  activity,  and  can  maintain 
a  high  independent  temperature. 

666.  It  would  seem,  however,  that  not  even  this  high  amount  of 
respiration  is  always  sufficient  for  Fishes  which  live  in  small  collections 
of  water,  where  their  temperature  is  liable  to  be  greatly  augmented  by 
the  heat  of  summer ;  under  which  condition,  there  is  an  increased  prone- 
ness  to  disintegration  in  their  tissues,  and  a  corresponding  necessity  for 
the  extrication  of  carbonic  acid  and  for  the  absorption  of  oxygen.  Many 
fresh-water  fishes,  under  such  circumstances,  may  be  seen  to  come  to  the 


RESPIRATION  IN   REPTILES.  371 

surface  and  to  swallow  air ;  and  it  would  seem  as  if  the  interior  of  the 
intestinal  canal  then  served  the  purpose  of  a  respiratory  surface,  the 
air  being  expelled  from  the  anus,  deprived  of  a  large  part  of  its  oxygen, 
and  highly  charged  with  carbonic  acid.  ^   ~ 

667.  In  addition  to  their  apparatus  for  aquatic  respiration,  many 
Fishes  are  provided,  in  their  air-bladder,  with  the  rudiments  of  the  air- 
breathing  apparatus  of  higher  animals ;  although  it  is  only  in  certain 
species,  which  approach  Reptiles  in  their  general  organization,  that 
this  really  affords  any  aid  in  the  aeration  of  the  blood.  The  air- 
bladder  in  its  simplest  condition  is  entirely  closed ;  and  it  is  then 
obviously  incapable  of  taking  any  share  in  the  respiratory  function, 
although  it  seems  to  be  an  organ  of  some  importance  to  the  animal,  in 
regulating  its  specific  gravity,  and  altering  its  position  in  the  water. 
In  other  cases,  it  communicates  with  the  intestinal  tube  by  a  short 
wide  canal,  termed  the  ductus  pneumaticus ;  and  this  may  serve  to 
admit  air,  which  is  taken  into  the  alimentary  tube  by  the  process  of 
swallowing  just  mentioned.  In  the  Reptilian  Fishes,  just  adverted  to, 
the  air-bladder  forms  a  double  sac,  which  is  evidently  the  ropresentative 
of  the  double  lung  of  the  air-breathing  Vertebrata ;  and  it  communi- 
cates with  the  back  of  the  mouth  by  a  regular  trachea  or  windpipe, 
which  has  a  muscular  valve  at  its  commencement,  serving  to  open  or 
to  close  its  orifice.  Some  of  these  fishes  are  able  to  live  for  a  consider- 
able time  out  of  water,  their  respiration  being  maintained  by  these 
rudimentary  lungs ;  and  they  can  also  make  a  hissing  sound,  by  the 
expulsion  of  the  contents  of  the  air-sacs  through  the  narrow  glottis,  or 
entrance  to  the  trachea. 

668.  The  condition  of  the  Respiratory  apparatus,  and  the  mode  in 
which  the  function  is  performed  in  the  class  of  Reptiles,  are  peculiarly 
interesting ;  as  it  is  in  this  class,  that  we  first  meet  with  the  complete 
adaptation  of  the  Yertebrated  structure  to  the  aeration  of  the  blood  by 
the  direct  influence  of  the  atmosphere.  Their  general  habits  of  life 
require  but  a  very  feeble  amount  of  aeration,  especially  at  moderate 
temperatures  ;  their  muscular  and  nervous  systems  being  usually  exer- 
cised in  a  very  low  degree ;  their  movements  being  sluggish,  and  their 
perceptions  obtuse.  In  fact,  they  may  be  considered,  on  the  whole, 
as  the  most  vegetative  of  all  Vertebrated  animals.  In  accordance 
with  this  character,  the  lungs  are  so  constructed  as  not  to  expose  any 
very  large  amount  of  blood  to  the  air  at  any  one  time ;  and,  as  we  have 
already  seen  (§  563),  only  a  portion  of  the  stream  of  the  circulation  is* 
diverted  to  the  lungs ;  the  main  current  being  sent  to  the  system,  with 
only  that  amount  of  aeration,  which  it  has  derived  from  the  admixture 
of  the  portion  of  blood  that  has  been  aerated  in  the  lungs,  with  the 

iMTjenous  current  that  has  last  been  returned  from  the  system. 

IK  ^^^-  ^^^  lungs  of  Reptiles  are,  for  the  most  part,  capacious  sacs, 
occupying  a  considerable  part  of  the  cavity  of  the  trunk ;  but  they  are 
very  slightly  subdivided,  so  that  the  amount  of  surface  they  can  expose 
is  really  small.  Where  any  subdivision  exists,  it  is  usually  at  the  upper 
extremity  of  the  lung,  near  the  point  of  entrance  of  the  bronchial  tube; 
and  where  there  is  no  actual  subdivision  of  the  cavity,  we  usually  find 
that  its  surface  is  extended  in  this  situation,  by  the  formation  of  a 
number  of  little  depressions '  or  pouches  in  its  walls,  upon  which  the 


372 


OF   RESPIRATION. 


blood-vessels  are  minutely  distributed.  The  greatest  amount  of  subdi- 
vision is  seen  in  the  lungs  of  the  Turtle  tribe ;  but  even  in  these,  the 
partitions  scarcelj  form  a  complete  division  at  any  part  of  the  lungs  ; 
and  the  ultimate  air-cells  are  of  very  large  size  (Fig.  105).  The  air- 
sacs  of  Reptiles  are  not  filled,  like  those  of 
Fig.  105.  Mammalia,  by  an  act  of  inspiration,  but  by  a 

process  of  swallowing,  which  is  comparativeljr 
tedious  ;  and,  from  the  small  amount  of  aerating 
surface,  in  proportion  to  the  amount  of  air  thus 
received  into  the  cavity,  one  inflation  of  the  air- 
sacs  lasts  for  a  considerable  time.  When  the 
replacement  of  oxygen  by  carbonic  acid  has 
proceeded  to  an  extent  that  renders  the  air  no 
longer  fit  to  remain  in  the  lungs,  these  cavities 
are  emptied  by  pressure  exercised  upon  them 
by  the  muscles  of  the  trunk ;  and  the  slow  exit 
of  the  air  through  the  narrow  glottis  is  accom- 
panied by  a  prolonged  hissing  sound,  which  is 
the  only  sort  of  voice  that  is  possessed  by  the 
greater  part  of  the  Reptile  class.  The  lungs 
are  again  filled  by  the  swallowing-process ;  and 
all  goes  on  as  before. 
Section  of  the  Lung  of  the  Turtle.  670.  Now  in  the  Frog  tribe,  which  forms  the 
lowest  order  of  Reptiles  (and  which  is  sometimes 
ranked  as  a  distinct' class,  under  the  title  of  Amphibia),  the  respiration 
during  the  early  or  Tadpole  state,  is  aquatic ;  being  carried  on  by 
means  of  gills,  and  conducted  exactly  upon  the  plan  of  that  of  Fishes. 
The  lungs  are  not  developed,  until  a  period  long  subsequent  to  the  ani- 
mal's emersion  from  the  egg ;  and  as  soon  as  they  are  ready  to  come 
into  play,  an  alteration  begins  to  take  place  in  the  circulating  system, 
by  which  the  current  of  blood  is  diverted  towards  them,  and  away  from 
the  gills  (§  562).  This  change  takes  place  to  its  full  extent  in  the  Frog, 
Toad,  Newt,  and  their  allies ;  which  henceforth  have  a  respiration  and 
a  circulation  exactly  analogous  to  that  of  Reptiles  in  general ;  but  it  is 
checked  in  the  Proteus,  Siren,  and  other  species,  which  form  the  peren- 
nihranchiate  group, — so  called  from  the  persistent  character  of  their 
gills,  which  still  remain  in  action,  the  lungs  never  being  sufficiently  de- 
veloped to  maintain  the  respiration  by  themselves.  The  curious  influ- 
ence which  Light  possesses  on  this  metamorphosis,  has  been  already  re- 
ferred to  (§  95). 

671.  This  order  Batrachia  is  further  distinguished  from  other  Rep- 
tiles, even  when  the  metamorphosis  is  complete,  by  the  softness  and 
nakedness  of  the  skin,  which  is  destitute  of  the  scales  and  horny  plates 
that  cover  it  in  the  Lizards,  Serpents,  and  Tortoises.  The  skin  of  the 
Frog  tribe  is  a  very  important  organ  of  respiration,  being  richly  sup- 
plied with  blood-vessels,  and  exposing  their  contents  to  the  influence  of 
the  air,  under  circumstances  nearly  as  favourable  as  those  aff"orded  by 
the  imperfectly-developed  lungs  of  these  animals.  Thus  a  Frog,  from 
which  the  lungs  have  been  removed,  will  live  a  considerable  time  at  a 
moderate  temperature,  if  its  skin  be  freely  exposed  to  a  moist  air )  for, 
in  consequence  of  the  peculiar  mode  in  which  the  circulation  is  carried 


RESPIRATION  IN   REPTILES  AND   BIRDS.  373 

on  in  these  animals  (§  561),  the  interruption  to  the  flow  of  blood 
through  the  lungs  does  not,  as  in  the  higher  classes,  produce  a  stagna- 
tion of  the  general  current  through  the  body ;  and  the  blood  receives, 
in  its  course  through  the  skin,  a  sufficient  amount  of  aeration  for  the_ 
support  of  life.  Indeed,  at  a  low  temperature,  the  influence  of  water 
on  the  skin  is  sufficient  (by  means  of  the  air  included  in  the  liquid)  to 
remove  the  small  amount  of  carbonic  acid  then  ready  for  excretion,  and 
to  supply  the  requisite  amount  of  oxygen ;  and  Frogs  may  thus  live 
beneath  the  water  for  any  length  of  time,  without  coming  to  the  surface 
to  breathe.  But  with  the  rise  of  the  temperature  of  their  bodies,  their 
blood  requires  a  higher  degree  of  aeration ;  and  they  then  come  to  the 
surface  to  take  in  air  by  the  mouth,  which  aerates  the  blood  through 
the  lungs.  It  appears  that,  during  the  heat  of  summer,  the  pulmonary 
respiration,  and  the  influence  of  the  water  on  the  skin,  are  not  sufficient ; 
as  it  is  found  that  Frogs  die,  if  they  are  confined  to  the  water  under 
such  circumstances, — their  natural  habit  being  to  quit  the  water  at 
such  times,  so  that  the  air  may  exert  its  full  influence  on  their  skin  as 
well  as  on  their  lungs.  They  do  not,  however,  quit  the  neighbourhood 
of  water,  and  soon  die  if  exposed  to  a  dry  atmosphere,  for,  if  the  skin 
become  dry,  its  aerating  function  can  be  no  longer  performed.  The 
same  result  happens  if  the  passage  of  gases  through  the  skin  be  impeded 
by  smearing  it  over  with  any  unctuous  substance.  We  shall  presently 
find  reason  to  believe  that  this  cutaneous  respiration  is  a  very  important 
part  of  the  function,  even  in  Man  and  Mammalia. 

672.  The  class  of  Birds  presents  a  most  striking  contrast  to  that  of 
Reptiles,  in  regard  to  the  energy  of  the  respiratory  function,  and  the 
extent  of  the  apparatus  destined  to  its  performance.  The  air-cells  are 
considerably  diminished  in  size,  so  that  the  extent  of  surface  over  which 
they  expose  the  blood  to  the  air  is  greatly  increased ;  and  there  even 
seems  reason  to  believe  that  th6  air  comes  into  direct  contact  with  the 
vessels  of  the  very  close  capillary  plexus  which  intervenes  between  the 
air-cells.  But  the  subdivision  of  the  lungs  is  not  carried  to  the  same 
degree  of  minuteness  as  it  is  in  Mammalia ;  and  the  required  extent  of 
surface  would  not  be  aff'orded  by  the  lungs  alone.  In  addition  to  these 
organs,  we  find  large  air-sacs,  communicating  with  them,  disposed  in 
difi"erent  parts  of  the  body, — such  as  the  abdominal  cavity,  the  inter- 
spaces among  the  muscles,  the  spaces  between  the  muscles  and  the 
skin,  &c.  These  very  greatly  increase  the  respiratory  surface,  their 
lining  membrane  being  extremely  vascular,  and  adapted  to  expose  the 
blood  to  the  influence  of  the  air.  In  most  Birds,  the  bones  themselves 
are  hollow,  and  the  lining  membrane  of  their  cavities  serves  as  an  addi- 
tional aerating  surface,  the  air  being  introduced  into  the  interior  of  the 
bones,  by  canals  that  communicate  directly  with  the  lungs.  So  free  is 
"  Is  communication,  that  the  respiration  has  been  known  to  be  main- 
lined through  the  fractured  humerus  of  an  Albatross,  when  an  attempt 
ras  made  to  destroy  the  bird  by  compressing  its  trachea.  Thus  the 
jspiratory  surface  is  extended  into  the  remoter  parts  of  the  system, 
rery  much  as  in  Insects ;  and  the  hollowness  of  the  bones,  together 
rith  the  presence  of  numerous  air-sacs  in  diff'erent  parts  of  the  body, 
sontribute  to  diminish  its  specific  gravity.     The  large  quantity  of  air 


374  OF  RESPIRATION. 

thus  included  in  different  portions  of  the  frame,  also  serves,  like  that 
contained  in  the  air-sacs  of  Insects,  as  a  reservoir  for  the  supply  of  the 
principal  aerating  organs  during  active  flight,  when  the  respiratory 
movements  are  less  free. 

673.  The  mechanism  of  Respiration  in  Birds  is  very  different  from 
that  which  produces  the  respiratory  movements  in  Mammalia.  The 
cavities  of  the  chest  and  thorax  are  not  yet  separated  by  a  diaphragm ; 
except  in  a  very  small  number  of  species,  that  approach  most  nearly  to 
the  next  class.  But,  on  the  other  hand,  the  whole  cavity  of  the  trunk 
is  more  completely  enclosed  in  a  bony  casing,  the  ribs  being  connected 
with  the  sternum  by  osseous  prolongations  from  the  latter,  instead  of 
by  cartilages,  and  the  sternum  itself  being  so  largely  developed,  as  to 
cover  almost  the  entire  front  of  the  body.  Now  the  natural  condition 
of  this  bony  framework  is  such,  that,  when  no  pressure  is  made  upon  it, 
the  cavity  it  encloses  is  in  a  state  of  distension;  and  the  state  of 
emptiness  can  only  be  produced  by  a  forcible  compression  of  the  frame- 
work, through  an  exertion  of  muscular  power.  The  lungs,  instead  of 
being  freely  suspended  in  the  cavity  of  the  chest,  as  in  Mammalia,  are 
attached  to  the  ribs ;  and  their  own  tissue  is  endowed  with  a  degree  of 
elasticity,  which  causes  them  to  dilate  when  they  are  permitted  to  do 
so.  In  the  state  of  distension,  therefore,  which  is  natural  to  the  cavity 
of  the  trunk,  the  lungs  are  expanded,  and  fill  themselves  with  air, 
which  they  draw  in  through  the  trachea ;  and  this  condition  they 
retain,  until,  by  the  action  of  the  external  muscles  upon  the  bony 
framework,  the  cavity  of  the  trunk  is  diminished,  and  the  air  is  expelled 
from  the  lungs  and  air-sacs,  which  are  again  filled  as  soon  as  the  pres- 
sure is  taken  off.  As  the  air-sacs  chiefly  communicate  with  the  part  of 
the  lungs  that  is  most  distant  from  the  trachea,  the  air  has  to  traverse 
the  whole  extent  of  those  last  organs,  both  when  it  is  being  drawn  into 
the  air-sacs,  and  when  it  is  being  expelled  from  them ;  so  that  it  is 
made  to  serve  for  the  aeration  of  the  blood  in  the  most  effectual  manner. 

674.  Thus,  although  the  respiratory  apparatus  of  Birds  does  not 
possess  the  highly  concentrated  development  which  we  shall  find  it  to 
present  in  Mammals,  it  serves,  by  the  extension  of  the  aerating  surface 
through  the  body,  to  bring  the  air  and  the  blood  into  most  intimate 
relation ;  and  the  energy  of  the  function  is  further  provided  for,  by  the 
mode  in  which  the  pulmonary  circulation  is  carried  on  (a  distinct  heart, 
as  it  were,  being  provided  for  it,  §  564),  as  well  as  by  the  arrangement 
of  the  blood-vessels,  which  transmit  to  the  respiratory  organs  the  whole 
of  the  blood  that  has  been  returned  in  a  carbonated  state  by  the  great 
veins  of  the  system.  The  very  large  proportion  of  red  corpuscles  con- 
tained in  the  blood  gives  additional  effect  to  these  provisions.  The 
very  high  amount  of  respiration  which  is  natural  to  Birds,  and  which 
cannot  be  suspended  even  for  a  short  time  without  fatal  consequences, 
has  a  direct  relation  (as  already  explained)  with  their  extraordinary 
muscular  activity,  as  well  as  with  the  high  bodily  temperature  which 
they  are  fitted  to  maintain,  and  which  cannot  be  lowered  in  any  great 
degree  without  the  suspension  of  their  other  functions.  Birds  are 
peculiarly  susceptible  of  impurities  in  the  atmosphere ;  and  it  has  been 
shown  by  experiment,  that  if  a  Bird,  a  Mammal,  and  a  Reptile,  be 


RESPIRATION  IN  BIRDS  AND   MAMMALS.  375 

aced  together  in  a  limited  quantity  of  air,  which  gradually  becomes 
vitiated  by  their  respiration,  the  Bird  will  die  first,  the  Mammal  next, 
and  the  Reptile  last.  Or  if  the  Bird  be  placed  alone  in  a  limited 
quantity  of  air,  and  be  left  until  the  atmosphere  is  so  vitiated  as  to  be  - 
no  longer  capable  of  supporting  its  life,  a  Mammal  will  still  live  for  a 
time  in  that  atmosphere ;  and  when  it  is  no  longer  fit  to  sustain  the 
life  of  the  Mammal,  the  Reptile  may  still  breathe  it  without  injury  for 
a  considerable  period.  There  is  strong  reason  to  believe,  indeed,  that, 
in  former  epochs  of  the  Earth's  history,  when  the  Reptile  class  was 
predominant,  supplying  the  place  of  Mammals  on  land,  and  of  Birds  in 
the  air,  the  atmosphere  was  so  highly  charged  with  carbonic  acid,  as 
not  to  be  capable  of  sustaining  the  life  of  the  higher  air-breathing  Ver- 
tebrata. 

3.  Mechanism  of  Respiration  in  Mammalia  and  in  Man. 

675.  It  is  in  the  class  of  Mammalia  that  we  find  the  Respiratory 
apparatus  presenting  its  highest  degree  of  concentration ;  and  the 
arrangements  for  its  action  the  most  complete.  The  Lungs  are  divided 
into  cavities  of  extreme  minuteness,  so  that  the  extent  of  surface  which 
they  expose  is  enormously  increased.  These  cavities,  or  air-cells,  are 
all  connected  with  the  trachea  by  means  of  the  bronchial  tubes  and 
their  minute  subdivisions ;  but,  on  account  of  the  minuteness  of  these 
passages,  a  considerable  force  would  be  required  to  inflate  the  air-cells 
with  air,  if  their  distension  were  to  be  accomplished  by  the  propulsion 
of  air  through  the  trachea,  as  we  have  seen  to  be  the  normal  mode  of 
inspiration  in  Reptiles.  Moreover,  if  the  air  were  introduced  in  this 
manner,  the  air-cells  would  be  the  last  portions  of  the  pulmonary  struc- 
ture that  would  be  distended  by  it,  as  well  as  the  first  to  be  emptied 
when  the  air  is  forced  out  again  by  external  pressure.  The  mechanism 
of  Respiration  in  Mammalia,  however,  is  so  arranged,  that  the  air  is 
most  efi*ectually  drawn  into  the  lungs,  instead  of  being  forced  into 
them ;  and  the  distension  of  the  air-cells  is  far  more  complete  than  it 
could  be  rendered  in  the  latter  method,  besides  being  accomplished  in  a 
much  shorter  time. 

676.  The  general  principle  of  the  operation  is  this.  The  lungs  are 
suspended  in  a  cavity  that  is  completely  closed,  being  bounded  above 
and  around  by  the  bony  framework  of  the  thordx,  the  interspaces  of 
which  are  filled  up  by  muscles  and  membranes,  and  being  entirely  cut 
ofi"  from  the  abdomen  below  by  the  diaphragm.  Under  ordinary  cir- 
cumstances, the  lungs  completely  fill  the  cavity ;  their  external  surface, 
covered  by  the  pleura,  being  everywhere  in  contact  with  the  pleural 
lining  of  the  thorax.  But  the  capacity  of  the  thoracic  cavity  is  sus- 
ceptible of  being  greatly  altered  by  the  movements  of  the  ribs,  and  by 
the  actions  of  the  diaphragm  and  abdominal  muscles,  as  will  presently 
be  explained  in  more  detail.  When  it  is  diminished,  the  lungs  are 
compressed,  and  a  portion  of  the  air  contained  in  them  is  expelled 
through  the  trachea.  On  the  other  hand,  when  it  is  increased,  the 
elasticity  of  the  air  within  the  lungs  causes  them  immediately  to  dilate, 
so  as  to  fill  the  vacuum  that  would  otherwise  exist  in  the  thoracic 


L 


376  OF   RESPIRATION. 

cavity ;  and  a  rush  of  air  takes  place  down  the  air-tubes,  and  into  the 
remotest  air-cells,  to  equalize  the  density  of  the  air  they  include  (which 
has  been  rarefied  by  the  dilatation  of  the  containing  cavities)  with  that 
of  the  surrounding  atmosphere. 

677.  The  diameter  of  the  ultimate  air-cells  of  the  Human  lung 
varies  from  about  the  l-200th  to  the  l-70th  of  an  inch.  Their  shape 
is  irregular,  and  their  walls  are,  for  the  most  part,  flattened  against 
each  other.  Each  of  the  ultimate  ramifications  of  the  bronchial  tubes 
communicates  with  a  cluster  of  these  air-cells  grouped  around  it ;  those 
which  are  in  immediate  proximity  with  the  tube  open  into  it  by  well- 
defined  circular  apertures,  and  the  others  communicate  with  it  by  open- 
ing into  these  and  into  each  other.  Each  air-cell  is  lined  by  an  exten- 
sion of  the  mucous  membrane  from  the  bronchial  tubes ;  but  this  does 
not  ^eem  to  be  furnished  with  an  epithelial  covering.  Between  the 
adjacent  air-cells,  is  a  network  of  fibrous  tissue,  that  forms  the  connect- 
ing medium  by  which  they  are  held  together ;  this  tissue  appears  to  be 
of  the  elastic  kind.  The  pulmonary  arteries  subdivide  into  branches, 
whose  ultimate  ramifications  form  an  extremely  minute  capillary  plexus ; 
and  this  is  disposed  between  the  walls  of  the  adjacent  air-cells,  so  that 
each  portion  of  this  plexus  comes  into  relation  with  the  air  (through  the 
lining  membrane  of  the  contiguous  air-cells)  on  both  sides, — an  arrange- 
ment which  is  obviously  the  most  favourable  that  can  be  to  the  aeration 
of  the  contained  blood.  It  has  been  calculated  by  M.  Rochoux,  that 
the  number  of  air-cells  grouped  around  each  terminal  bronchus  is  little 
less  than  18,000 ;  and  that  the  total  number  in  the  lungs  amounts  to 
six  hundred  millions.  If  this  estimate  be  even  a  remote  approximation 
to  the  truth,  it  is  evident  that  the  amount  of  surface  exposed  by  the 
walls  of  these  minute  cavities,  must  be  very  many  times  greater  than 
that  of  the  whole  exterior  of  the  body. 

Fig.  106. 


Arrangement  of  the  Capillaries  of  the  ait-cells  of  the  Human  Lung. 

678.  The  larger  bronchial  tubes  are  more  or  less  cartilaginous ;  but  the 
smaller  branches  do  not  possess  any  such  deposit  in  their  walls,  though 
still  retaining  their  circular  form.  We  find  in  the  latter  a  fibrous 
structure,  which  seems  to  possess  ,the  properties  of  non-striated  muscle ; 
and  by.  this,  the  diameter  of  these  tubes  appears  to  be  governed.     The 


STRUCTURE   OF   THE   LUNGS  IN  MAN.  377 

contractility  of  the  walls  of  the  smaller  bronchi  may  be  excited  by 
chemical,  electrical,  or  mechanical  stimuli  applied  to  themselves  ;  though 
it  is  not  so  readily  caused  to  manifest  itself  by  stimulating  the  nerves. 
By  the  continued  influence  of  galvanism,  bronchial  tubes  of  a  line  ia 
diameter  have  been  made  to  contract,  until  their  cavity  was  nearly  oblite- 
rated ;  and  it  has  been  found  by  Volkmann  that  a  similar  effect  may  be 
produced  by  galvanising  the  Par  Vagum.  Supposing  the  muscular 
fibres  of  the  bronchial  tubes  to  contract  during  expiration,  the  effect  of 
such  contraction  would  be  to  diminish  both  the  length  and  the  diameter 
of  the  tubes,  and  thus  to  force  out  their  contained  air.  Whether  such 
contraction,  alternating  with  relaxation,  takes  place  automatically,  as  a 
part  of  the  ordinary  rhythmical  movements  of  respiration,  has  not  yet 
been  clearly  made  out ;  but  in  its  tonic  form,  it  manifests  itself  strongly 
in  certain  diseased  conditions,  especially  in  spasmodic  Asthma,  which 
appears  essentially  to  consist  in  a  contracted  state  of  the  smaller 
bronchial  passages,  occasioning  an  interruption  to  the  passage  of  air 
through  them.  It  is  interesting  to  observe,  that  the  contractility  of  the 
muscular  walls  of  these  tubes  has  been  experimentally  found  to  be 
greatly  diminished  by  the  application  of  vegetable  narcotics,  especially 
stramonium  and  belladonna, — substances  which  are  well-known  to  have 
a  powerful  remedial  influence  in  spasmodic  Asthma. 

679.  The  Lungs  themselves  appear  to  be,  almost  entirely,  passive 
instruments  of  the  Respiratory  function.  Their  contraction  when  over- 
distended,  and  their  dilatation  after  extreme  pressure,  may  be  partly  due 
to  the  elasticity  of  their  structure ;  which  seems  to  produce,  when  acting 
by  itself,  a  moderately-distended  state  of  the  air-cavities.  This,  too,  is 
the  condition  that  seems  most  natural  to  the  cavity  of  the  chest ;  the 
fullest  dilatation,  or  the  most  complete  contraction,  of  which  it  is  capa- 
ble, being  only  accomplished  by  a  forcible  effort. 

680.  The  dilatation  of  the  cavity  of  the  chest,  which  constitutes 
Inspiration,  is  accomplished  by  two  sets  of  movements ; — the  elevation 
of  the  ribs,  and  the  depression  of  the  diaphragm.  From  the  peculiar 
mode  in  which  the  ribs  are  articulated  with  the  spinal  column  at  one 
extremity,  and  from  the  angle  which  they  make  with  the  cartilages  that 
connect  them  to  the  sternum  at  the  other,  the  act  of  elevation  tends  to 
bring  the  ribs  and  the  cartilages  more  into  a  straight  line,  and  to  carry 
the  former  to  a  greater  distance  from  the  median  plane  of  the  body, 

'  whilst  the  sternum  is  also  thrown  forwards.  Consequently  the  eleva- 
tion of  the  ribs  increases  the  capacity  of  the  thorax,  upwards,  forwards, 
and  laterally.  The  movement  is  chiefly  accomplished  by  the  Scaleni 
muscles,  which  draw  up  the  first  rib ;  and  by  the  Intercostals,  which 
draw  the  other  ribs  into  nearer  proximity  with  each  other,  so  that  the 
total  amount  of  movement  in  each  rib  increases  as  we  pass  from  above 
downwards, — every  one  being  drawn  up  by  its  connexion  with  the 
one  above  it,  and  being  drawn  nearer  to  it  by  the  action  of  its  own 
intercostals.  The  elevation  of  the  ribs  is  further  assisted  by  the  Ser- 
ratus  magnus,  and  by  other  muscles  connected  with  the  spine  and  the 

I  scapula  ;  and  when  the  respiratory  movement  is  very  forcibly  performed, 
the  scapula  is  itself  drawn  upwards,  by  the  muscles  that  descend  to  it 


378  OF  RESPIRATION. 

an  unusual  enlargement  of  the  upper  part  of  the  thoracic  cavity. — When 
the  Expiratory  action  is  to  be  performed,  the  descent  of  the  ribs  is 
occasioned  by  the  muscles  of  the  spine  and  abdomen,  which  proceed 
upwards  from  the  lower  part  of  the  trunk ;  and  this  action  is  aided  by 
the  elasticity  of  the  costal  cartilages. 

681.  In  the  ordinary  act  of  inspiration,  however,  the  Diaphragm 
performs  the  most  important  part.  The  contraction  of  this  muscle 
changes  its  upper  surface,  from  the  high  arch  that  it  forms  when 
relaxed  and  pushed  upwards  by  the  viscera  below,  to  a  much  more  level 
state ;  though  it  never  approaches  very  closely  to  a  plane ;  being  some- 
what convex,  even  when  the  fullest  inspiration  has  been  taken.  When 
thus  drawn  down,  it  presses  upon  the  abdominal  viscera,  and  causes 
them  to  project  forwards,  which  they  are  allowed  to  do,  by  the  relaxa- 
tion of  the  abdominal  muscles.  In  tranquil  breathing,  this  action  is 
alone  nearly  sufficient  to  produce  the  requisite  enlargement  of  the  tho- 
racic cavity ;  the  position  of  the  ribs  being  very  little  altered.  In  the 
expiratory  movement,  the  diaphragm  is  altogether  passive ;  for,  being 
in  a  state  of  relaxation,  it  is  forced  upwards  by  the  abdominal  viscera, 
which  are  pressed  inwards  by  the  contraction  of  the  abdominal  muscles. 
These  last,  therefore,  are  the  main  instruments  of  the  expiratory  move- 
ment; diminishing  the  cavity  of  the  chest  by  elevating  its  floor, 
at  the  same  time  that  they  draw  its  bony  framework  into  a  narrower 
compass. 

682.  In  this  manner,  by  the  regularly-alternating  dilatation  and  con- 
traction of  the  thoracic  cavity,  the  air  within  the  lungs  is  alternately  in- 
creased and  diminished  in  amount;  and  thus  a  regular  exchange  is 
secured.  This  exchange,  however,  can  only  afi*ect  at  any  one  time  a 
certain  proportion  of  the  air  in  the  lungs ;  thus  it  is  probable,  that  the 
quantity  remaining  in  these  organs  after  ordinary  expiration  is  above 
100  cubic  inches,  whilst  the  amount  usually  expired  is  not  above  20 
cubic  inches.  Indeed  if  it  were  not  for  the  tendency  of  gases  to  mutual 
diffusion,  the  air  in  the  remote  air-cells  might  never  be  renewed. — If 
any  aperture  exist,  by  which  air  could  obtain  direct  access  to  the  pleural 
cavity,  the  lungs  would  not  be  dilated  by  its  enlargement;  for  the 
vacuum  would  be  supplied  much  more  readily,  by  the  direct  ingress  of 
the  air  (provided  the  aperture  be  large  enough),  than  by  the  distension 
of  the  lung.  Thus  a  large  penetrating  wound  of  the  thoracic  cavity 
may  completely  throw  out  of  use  the  lung  of  that  side ;  and  the  same 
result  will  follow,  when  an  aperture  forms  by  ulceration  in  the  sub- 
stance of  the  lung  itself,  establishing  a  free  communication  between  the 
pleural  cavity  and  one  of  the  bronchial  tubes  ;  so  that,  of  the  air  which 
rushes  in  by  the  trachea,  to  compensate  for  the  enlargement  of  the  thoracic 
cavity,  a  great  part  goes  at  once  into  that  cavity,  without  contributing 
to  the  distension  of  the  lungs,  and  therefore  without  serving  for  the 
aeration  of  the  blood. 

683.  The  number  of  the  respiratory  movements  (that  is,  of  the  acts 
of  inspiration  and  expiration  taken  together)  may  be  probably  estimated 
at  from  14  to  18  per  minute,  in  a  state  of  health,  and  of  repose  of  body 
and  mind.  Of  these,  the  greater  part  are  moderate  in  amount,  involv- 
ing little  movement  except  in  the  diaphragm ;  but  a  greater  exertion, 


MECHANISM   OF   RESPIBATION  IN  MAN.  379 

attended  with  a  decided  elevation  of  the  ribs,  is  usually  made  at  every 
fifth  recurrence.  The  frequency  of  the  respiratory  movements,  how- 
ever, is  liable  to  be  greatly  increased  by  various  causes,  such  as  violent 
muscular  exertion,  mental  emotion,  or  quickened  circulation ;  whilst  it 
may  be  diminished  by  the  torpidity  of  the  nervous  centres,  on  whose 
agency  the  movement  depends, — as  we  see  in  apoplexy,  narcotic  poison- 
ing, &c.  An  acceleration  seems  very  constantly  to  take  place  in  dis- 
eases, which  unfit  a  part  of  the  lung  for  the  performance  of  its  func- 
tion ;  and  the  rate  bears  a  proportion  to  the  amount  thus  thrown  out  of 
use.  Thus,  the  usual  proportion  between  the  respiratory  movements  and 
the  pulse  being  as  1  to  4J  or  5,  it  may  become  in  Pneumonia  as  1 
to  3,  or  even  in  severe  cases  1  to  2 ;  the  increase  in  the  number  of 
respiratory  movements  being  much  greater  in  proportion,  than  the  aug- 
mentation of  the  rate  of  the  pulse.  But  it  must  be  remembered  by  the 
practitioner,  that  a  simply  hysterical  state  may  produce,  in  young 
females,  an  extraordinary  acceleration  of  the  respiration ;  the  number 
of  movements  being  sometimes  no  less  than  100  per  minute.  There 
will  be  a  great  increase,  also,  in  the  number  of  inspirations,  when  the 
regular  movements  are  prevented  from  being  fully  performed,  by  any 
cause  that  afi"ects  their  mechanism,  even  whilst  the  lungs  themselves 
are  quite  sound.  Thus  in  inflammation  of  the  pleura  or  pericardium, 
or  in  rheumatic  affections  of  the  intercostal  muscles,  the  full  action  of 
the  ribs  is  prevented  by  the  pain  which  the  movements  produce ;  and 
the  same  is  the  case  in  regard  to  the  diaphragm,  when  the  peritoneum 
or  the  abdominal  viscera  are  affected  with  inflammation.  Under  such 
circumstances,  there  is  an  involuntary  tendency  to  make  up  for  the  de- 
ficiency in  the  amount  of  the  respiratory  movements,  by  an  increase  in 
their  number. 

684.  The  combined  actions  of  the  respiratory  muscles,  which  have 
been  now  explained,  belong  to  the  group  termed  reflex ;  being  the  result 
of  the  operation  of  a  certain  part  of  the  nervous  centres,  which  does 
not  involve  the  will,  or  even  sensation,  and  which  may  continue  when 
all  the  other  parts  of  the  nervous  centres  have  been  removed.  In  the 
Invertebrated  Animals,  we  commonly  find  a  distinct  ganglionic  centre 
set  apart  for  the  performance  of  the  respiratory  movements ;  and  the 
division  of  the  nervous  centres  in  Vertebrated  animals,  which  is  the 
seat  of  the  same  function,  may  be  clearly  marked  out,  although  it  is  not 
so  isolated  from  the  rest.  It  is,  in  fact,  that  segment  of  the  Medulla 
Oblongata  and  upper  part  of  the  Spinal  Cord,  which  is  connected  with 
the  5th,  7th,  and  8th  pairs  of  cephalic  nerves,  and  with  the  phrenic. 
The  entire  brain  may  be  removed  from  above  (by  successive  slicing), 
and  the  whole  spinal  cord  may  be  destroyed  below ;  and  yet  the  respi- 
ratory movements  of  the  diaphragm  will  still  continue, — those  of  the 
intercostal  and  other  muscles  being  of  course  suspended,  by  the  destruc- 
tion of  that  portion  of  the  cord  from  which  their  nerves  arise.  But  if 
the  spinal  cord  be  divided,  between  the  point  at  which  it  receives  the 
5th  and  8th  pairs  of  nerves,  and  that  at  which  it  gives  origin  to  the 
phrenic,  the  movements  of  the  diaphragm  immediately  cease ;  and  this 
is  the  reason  why  deatl;i  is  so  instantaneous,  in  cases  of  luxation  or  frac- 
ture of  the  higher  cervical  vertebrae,  causing  pressure  upon  the  spinal 


380  OF   RESPIRATION. 

cord  just  below  its  exit  from  the  cranium ;  whilst  if  the  injury  take 
place  below  the  origin  of  the  phrenic  nerve,  life  may  be  prolonged  for 
some  time. 

685.  The.  Respiratory  movements,  like  other  reflex  actions  (§  394), 
depend  upon  a  stimulus  of  some  kind,  originating  at  the  extremities  of 
the  nerves,  propagated  towards  the  centre  by  the  aff'erent  trunks,  an 
giving  rise  to  a  motor  impulse,  which  is  transmitted  along  the  eff'erent 
or  motor  nerves  to  the  muscles,  and  which  occasions  their  contraction. 
Now  the  importance  of  the  respiratory  function  to  the  maintenance  of 
life  which  has  already  been  sufficiently  pointed  out,  necessitates  an 
ample  provision  for  its  due  performance ;  and  thus  we  find  that  the 
stimulus  for  the  excitement  of  the  movements  may  be  transmitted 
through  several  channels.  Its  chief  source,  no  doubt,  is  in  the  lungs ; 
and  arises  from  the  presence  of  venous  blood  in  the  capillaries,  and  of 
carbonic  acid  in  the  air-cells.  Under  ordinary  circumstances, — that  is, 
when  the  blood  is  being  duly  aerated,  and  the  air  being  properly  renewed, 
— the  impression  thus  made  upon  the  nerves  of  the  lungs  is  so  faint,  that 
we  cannot  perceive  it,  even  when  we  specially  direct  our  attention  to  it. 
But  if  we  suspend  the  movements  for  a  moment  or  two,  we  immediately 
experience  a  sensible  uneasiness.  The  Par  Yagum  is  obviously  the 
channel,  through  which  this  impression  is  conveyed  to  the  nervous  cen- 
tres ;  and  it  is  found  that,  if  the  trunk  of  this  nerve  be  divided  on  both 
sides,  the  respiratory  movements  are  greatly  diminished  in  frequency. 
Hence  it  is  undoubtedly  one  of  the  principal  excitors  of  the  respiratory 
movements. 

636.  But  the  sensory  nerves  of  the  general  surface,  and  more  parti- 
cularly the  sensory 'portion  of  the  Fifth  pair,  which  supplies  the  face, 
are  most  important  auxiliaries,  as  excitor  nerves ;  the  inspiratory  move- 
ment being  peculiarly  and  forcibly  excited  by  impressions  made  upon 
them,  especially  by  the  contact  of  cold  air  or  water  with  the  face. 
The  power  of  the  impression  made  by  the  air  upon  the  general  surface, 
and  particularly  upon  the  face,  in  exciting  the  inspiratory  movement, 
is  well  seen  in  the  case  of  the  first  inspiration  of  the  new-born  infant^ 
which  appears  to  be  excited  solely  in  this  manner.  An  inspiratory 
effort  is  often  made,  as  soon  as  the  face  has  emerged  from  the  Vagina 
of  the  mother;  whilst,  on  the  other  hand,  if  the  face  be  prevented 
from  coming  into  contact  with  cool  air,  the  inspiratory  efi'ort  may  be 
wanting.  When  it  does  not  duly  take  place,  it  may  often  be  excited 
by  a  slap  with  the  flat  of  the  hand  upon  the  nates  or  abdomen  ;  a  fact 
which  shows  the  special  influence  of  impressions  upon  the  general 
surface,  in  rousing  the  motor  impulse  in  the  Medulla  Oblongata,  and 
in  causing  its  transmission  to  the  muscles.  The  deep  inspirations  which 
follow  a  dash  of  cold  water  upon  the  face,  or  the  descent  of  the  cold 
douche  or  of  the  divided  streams  of  the  shower-bath  upon  the  body,  or 
the  shock  of  immersion  in  the  cold  plunge-bath,  all  testify  to  the 
powerful  influence  of  such  impressions  in  the  adult ;  and  the  efficacy 
of  other  kinds  of  irritation  of  the  skin,  such  as  beating  with  holly- 
twigs,  in  maintaining  the  respiratory  movements  in  cases  of  narcotio 
poisoning,  shows  that  the  required  impressions  are  not  restricted  to 
the  contact  of  cold  air  or  water.     It  seems  probable,  from  various  facts. 


REFLEX  CHARACTER   OF   RESPIRATORY  MOVEMENT.  381 

that  the  presence  of  venous  blood  in  the  arterial  capillaries  of  the 
system,  and  the  consequent  stagnation  in  the  current  through  them 
(§  597),  may  exert  an  influence  through  the  Sympathetic  nerves :  which 
may  be  transmitted,  by  the  copious  inosculations  of  that  system  with 
the  Par  Vagum,  to  the  Medulla  Oblongata;  and  which. may  there  serve 
as  a  valuable  auxiliary  in  exciting  the  respiratory  movements. 

687.  Of  the  mode  in  which  the  impressions,  thus  transmitted  to  the 
Medulla  Oblongata,  act  in  exciting  the  motor  impulses  which  issue 
from  it,  nothing  is  known;  but  these  impulses,  directed  along  the 
phrenic,  intercostal,  and  other  nerves,  produce  the  requisite  movements. 
When  the  stimulus  is  unusually  strong,  various  nerves  and  muscles 
are  put  in  action,  which  do  not  co-operate  in  the  ordinary  movements 
of  inspiration  ;  and  it  may  sometimes  be  observed,  that  movements  are 
thus  excited  in  parts,  which  will  not  act  in  obedience  to  the  will,  being 
to  all  appearance  completely  paralysed.  This  fact  shows  how  com- 
pletely the  class  of  actions  in  question  is  independent  of  the  influence  of 
the  mind ;  but  we  must  not  lose  sight  of  the  control  which  the  mind, 
especially  in  the  higher  classes  of  animals,  possesses  over  them.  Va- 
rious actions  of  the  respiratory  muscles,  particularly  those  of  weeping 
and  laughing,  are  the  most  direct  means  of  expressing  the  passions  and 
emotions  of  the  mind  ;  and  are  involuntarily  excited  by  these.  And, 
again,  the  respiratory  actions  are  placed  in  a  certain  degree  under  the 
control  of  the  Will ;  in  order  that  they  may  be  subservient  to  the  pro- 
duction of  vocal  sounds,  and  to  the  actions  of  speech,  singing,  &c.  The 
will  cannot  long  suspend  the  respiratory  movements ;  for  the  stimulus 
to  their  involuntary  performance  soon  becomes  too  powerful  to  be  any 
longer  resisted.  And  it  is  well  that  it  should  be  so  ;  for  if  the  perfor- 
mance of  this  most  important  function  were  left  to  our  own  choice,  a 
few  moments  of  forgetfulness  would  be  productive  of  fatal  results.  But 
it  is  to  the  power  which  the  will  possesses,  of  directing  and  controlling 
the  respiratory  movements,  that  we  owe  the  faculty  of  producing  arti- 
culate sounds,  and  thus  of  holding  the  most  direct  and  intimate  con- 
verse with  each  other. 

688.  It  is  essential  for  the  due  performance  of  the  respiratory  move- 
ments, that  the  portion  of  the  nervous  centres,  on  which  they  depend, 
should  be  in  a  state  of  activity.  This  is  the  case,  under  ordinary  cir- 
cumstances, throughout  life.  The  state  of  perfect  quiescence,  to  which 
the  Brain  is  liable,  never  affects  the  Medulla  Oblongata ;  and  the  respi- 
ratory movements  are  consequently  kept  up  with  as  much  regularity 
and  energy  (in  proportion  to  the  requirements  of  the  system),  during 
our  sleeping,  as  during  our  waking  hours.  But  if  any  cause  induce 
torpidity  of  the  medulla  oblongata,  the  respiratory  movements  are  then 
retarded,  or  even  suspended  altogether ;  and  all  the  consequences  of 
the  cessation  of  the  aeration  of  the  blood  speedily  develope  themselves 
(§  706).  This  is  seen  in  apoplexy ;  when  the  pressure,  or  other  cause 
of  suspended  activity,  which  at  first  affected  the  brain  alone,  gradually 
propagates  its  influence  downwards.  The  same  is  the  case  in  narcotic 
poisoning ;  in  which  also  the  brain  is  the  first  to  be  aff'ected,  and  may 
suffer  alone  ;  but  if  the  noxious  influence  be  propagated  to  the  medulla 
oblongata,  it  manifests  itself  in  the  retardation  of  the  respiratory  move- 


382  OE'  RESPIRATION. 

ments,  and,  when  sufficiently  powerful,  in  their  complete  suspension. 
Under  such  circumstances,  it  is  requisite  to  resort  to  all  possible  means 
of  keeping  up  the  respiratory  movements  ;  and  when  these  fail,  arti- 
ficial respiration  may  be  successfully  employed.  For  if,  by  such 
means,  the  circulation  can  be  prevented  from  failing  for  a  sufficient 
length  of  time,  the  ordinary  processes  of  nutrition  go  on,  the  poisonous 
matter  is  gradually  decomposed,  or  eliminated  by  the  secreting  organs ; 
and  the  nervous  centres  resume  their  usual  functions.  A  torpid  con- 
dition of  the  medulla  oblongata,  inducing  a  retardation  of  the  respira- 
tory movements,  seems  to  be  one  of  the  morbid  conditions  attendant 
upon  typhoid  fever ;  and  probably  depends  in  the  first  instance  upon  a 
disordered  state  of  the  blood,  which  does  not  exert  its  usual  vivifying 
influence.  In  such  cases,  the  proportion  of  the  respiratory  movements 
to  the  pulse  sinks  as  low  as  1  to  6,  or  even  as  1  to  8  ;  and  thus  the 
due  aeration  of  the  blood  is  not  performed,  and  its  stimulating  proper- 
ties are  still  further  diminished. 

4.    Chemical  Phenomena  of  Respiration. 

689.  Having  now  fully  considered  the  means,  by  which  the  Atmo- 
sphere and  the  Blood  are  brought  into  relation  in  the  lungs,  we  have 
to  examine  into  the  results  of  their  mutual  action.  It  will  be  remem- 
bered that  the  Atmosphere  contains  about  21  per  cent,  of  Oxygen  to 
79  of  Nitrogen,  by  measure  ;  or  23  parts  of  Oxygen  to  77  of  Nitrogen, 
by  weight.  The  changes  which  it  undergoes  in  Respiration  may  be 
considered  under  four  heads : — 1.  The  disappearance  of  Oxygen,  which 
is  absorbed.  2.  The  presence  of  Carbonic  Acid,  which  has  been  exhaled. 
3.  The  absorption  of  Nitrogen.  4.  The  exhalation  of  Nitrogen.  Of 
these,  the  first  two  are  by  far  the  most  important. — It  was  formerly 
supposed  that  the  Oxygen  which  disappears,  is  the  precise  equivalent 
of  the  Carbonic  Acid  which  is  set  free  (the  latter  gas  containing  its 
own  bulk  of  the  former) ;  and  that  the  union  of  the  absorbed  oxygen 
with  the  carbon  to  be  eliminated,  takes  place  in  the  lungs.  It  is  now 
known,  however,  that  the  carbonic  acid  is  given  out  ready  formed,  its 
production  having  taken  place  at  the  expense  of  oxygen  previously 
contained  in  the  blood ;  and  that  a  much  larger  proportion  of  oxygen  is 
usually  absorbed,  than  is  contained  in  the  carbonic  acid  exhaled,  the 
difference  sometimes  exceeding  the  thirds  part  of  the  carbonic  acid 
formed,  whilst  it  is  sometimes  so  small  that  it  may  be  disregarded. 
This  diversity  seems  to  depend,  partly  upon  the  constitution  of  the 
species  experimented  on,  and  partly  upon  the  degree  of  development  of 
the  individual,  but  in  great  part  upon  the  nature  of  the  food ;  it  having 
been  established  by  the  recent  experiments  of  MM.  Regnault  and 
Reiset,  that  the  quantity  of  oxygen  absorbed  into  the  system  is  much 
greater  on  an  animal  diet,  than  on  a  farinaceous.  It  is  certain  that,  of 
this  absorbed  oxygen,  a  part  must  enter  into  combination  with  the  sul- 
phur and  phosphorus  of  the  original  components  of  the  body,  converting 
these  into  sulphuric  and  phosphoric  acids ;  and  the  remainder  must  enter 
into  other  chemical  combinations,  very  probably  uniting  with  the  hydro- 


AMOUNT   OF   CAKBONIC  ACID   EXHALED.  383 

gen  of  the  fatty  matter,  to  form  part  of  the  water  which  is  exhaled  from 
the  lungs. 

690.  This  interchange  would  seem  to  depend  upon  the  tendency 
which  all  gases  have  to  mutual  admixture,  when  they  are  separated 
by  a  porous  septum.  According  to  the  law  discovered  by  Prof.  Gra- 
ham, the  relative  volumes  of  the  gases  which  will  thus  replace  each 
other,  are  inversely  as  the  square-roots  of  their  specific  gravities ;  thus, 
the  specific  gravity  of  oxygen  being  to  that  of  hydrogen  as  16  to  1,  the 
replacing  volume  of  oxygen  is  to  that  of  hydrogen  as  1  to  4.  The 
same  holds  good,  when  one  of  the  gases  is  absorbed  by  a  liquid ;  pro- 
vided the  replacing  gas  be  also  capable  of  being  absorbed  to  the  same 
extent.  On  this  principle,  the  replacing  volume  of  oxygen  is  to  that 
of  carbonic  acid  as  1174  to  1000 ;  but  as  the  actual  amounts  inter- 
changed do  not  constantly  follow  this  ratio,  it  is  obvious  that  they  are 
liable  to  be  modified  by  other  conditions,  these  being  chiefly  (it  seems 
probable)  the  relative  quantities  of  the  two  gases  already  present  in  the 
blood,  and  the  relative  facility  with  which  they  are  absorbed  into  it  or 
extricated  from  it. 

691.  It  is  difficult  to  form  an  exact  estimate  of  the  actual  quantity 
of  Carbon,  thrown  off  from  the  lungs  in  the  form  of  Carbonic  Acid 
during  any  lengthened  period:  since  the  amount  disengaged  during 
experiments  carried  on  for  a  limited  time,  cannot,  for  many  reasons,  be 
taken  as  affording  a  fair  average.  Thus  the  quantity  will  vary  with 
the  extOrnal  temperature,  with  the  state  of  previous  rest  or  activity, 
with  the  length  of  time  that  has  elapsed  since  a  meal,  and  particularly 
with  the  general  development  of  the  body.  The  amount  of  carbonic 
acid  exhaled  is  greatly  increased  by  external  cold ;  as  is  shown  in  the 
results  of  such  experiments  as  the  following. — Small  Birds  and  Mam- 
mals having  been  enclosed  in  a  limited  quantity  of  air,  for  the  space  of 
an  hour,  at  ordinary  temperatures,  the  quantity  of  carbonic  acid  they 
produced  was  noted.  The  experiment  was  then  repeated  at  a  tempera- 
ture nearly  approaching  that  of  the  body ;  and  was  performed  a  third 
time  at  a  temperature  of  about  32°.  The  following  are  the  comparative, 
amounts. 

Temp.  59°— 68°.  Temp.  86°— 106°.  Temp,  about  32°. 

Grammes.  Grammes.  Grammes. 

A  Canary,  0-250  0-129  0-325 

A  Turtle-dove,  0-684  0-366  0-974 

Two  Mice,  0-498  0-268  ^                 0-581 

A  Guinea-pig,  2-080  1-453  8-006 

Thus  it  would  appear  that  the  quantity  of  carbonic  acid  exhaled  between 
86°  and  106°  is  not  much  more  than  half  of  that  which  is  exhaled  be- 
tween 59°  and  68°  ;  and  is  only  about  two-ffths  of  that  which  is  given 
off"  at  32°. 

692.  The  quantity  of  Carbonic  Acid  exhaled  during  exercise,  and  for 
a  certain  time  after  it,  and  also  after  a  full  meal,  is  considerably  in- 
creased ;  whilst  on  the  other  hand,  it  is  greatly  diminished  during  sleep. 
Thus  a  person  who  was  excreting  145  grains  of  carbon  per  hour,  whilst 
fasting  and  at  rest,  excreted  165  after  dinner,  and  190  after  breakfast 
and  a  walk ;  whilst  he  only  excreted  100  during  sleep.     The  variation 


384  OF  RESPIRATION. 

with  the  general  development  of  the  body,  and  also  with  the  sex  and 
age,  is  considerable.  Thus,  the  exhalation  is  almost  always  greater  in 
males,  than  in  females  of  the  same  age,  at  every  period  of  life  except 
childhood.  In  males,  the  quantity  increases  regularly  from  eight  to 
thirty  years  of  age,  remaining  nearly  stationary  until  forty ; — thus  it 
averages  77*5  grains  of  carbon  per  hour  at  eight  years;  135  grains  at 
fifteen ;  176*7  grains  at  twenty ;  and  189  grains  from  thirty  to  forty. 
Between  forty  and  fifty,  there  is  a  well-marked  diminution,  the  average 
being  then  156  grains ;  and  the  diminution  continues  up  to  extreme  old 
age,  when  the  amount  exhaled  scarcely  exceeds  that  which  is  extricated 
at  ten  years  of  age ;  thus,  between  sixty  and  eighty,  it  was  142*5 
grains;  and  in  a  man  of  a  hundred  and  two,  it  was  only  91*5  grains. 
These  average  results,  however,  are  widely  departed  from  in  individual 
cases ;  an  extraordinary  development  of  the  muscular  system  being  al- 
ways accompanied  by  a  high  rate  of  extrication  of  carbon ;  and  vice 
versd.  Thus  a  man  of  remarkable  muscular  vigour,  whose  age  was 
twenty-six  years,  exhaled  217  grains  of  carbon  in  an  hour ;  a  robust 
man  of  sixty  exhaled  209*4  grains;  and  an  old  man  of  ninety-two,  who 
in  his  younger  days  had  possessed  uncommon  muscular  power,  and  who 
preserved  a  remarkable  degree  of  energy,  still  gave  forth  at  the  rate  of 
151  grains  per  hour.  On  the  other  hand,  a  man  of  slight  muscular 
development,  at  the  age  of  forty-five,  only  exhaled  132  grains ;  and  an- 
other at  the  age  of  seventy-six,  only  92*4  grains. 

693.  In  females,  nearly  the  same  proportional  increase  goes  on,  up 
to  the  time  of  puberty ;  when  the  quantity  abruptly  ceases  to  increase, 
and  remains  stationary  so  long  as  menstruation  continues  regular.  The 
average  quantity  of  carbonic  acid  exhaled  by  girls  nearly  approaching 
puberty,  is  about  100  grains  per  hour ;  and  it  remains  at  this  standard 
until  nearly  the  close  of  menstrual  life.  At  the  period  of  the  cessation 
of  the  catamenia,  it  undergoes  a  perceptible  increase ;  the  average  be- 
tween forty  and  fifty  years  of  age,  being  about  130  grains  per  hour ; 
and  the  quantity  exhaled  in  a  woman  of  great  muscular  development, 
and  of  forty-four  years  of  age,  rising  to  152*4  grains  in  an  hour.  After 
the  age  of  fifty,  or  thereabouts,  the  quantity  decreases,  as  in  men.  It  is 
remarkable  that,  during  pregnancy,  there  is  the  same  increase  in  the 
exhalation  of  carbon,  as  there  is  after  the  final  cessation  of  the  cata- 
menia ;  and  the  same  takes  place,  if  the  menstrual  discharge  be  tem- 
porarily suspended,  through  any  other  cause. 

694.  It  is  obviously  difficult,  then,  to  obtain  exact  estimates,  from 
any  experiments  conducted  for  a  short  time  only,  of  the  total  amount 
of  Carbon  thrown  ofi*  during  a  lengthened  period ;  since  the  condition 
of  the  individual  varies  so  greatly  at  different  times ;  and  the  variation 
amongst  different  individuals  is  so  great.  Moreover,  of  the  total  amount 
of  carbon  excreted  in  a  gaseous  form,  a  certain  part  is  undoubtedly  set 
free  from  the  skin ;  but  the  proportion  of  this  does  not  seem  to  be  con- 
siderable. As  a  means  of  measuring  the  whole  quantity  of  carbonic 
acid  set  free,  without  causing  the  respiratory  movements  to  be  per- 
formed in  any  unnatural  manner,  Prof.  Scharling  constructed  an  air- 
tight chamber,  of  dimensions  sufficient  to  allow  an  individual  to  remain 
in  it  for  some  time  without  inconvenience ;  and  so  arranged,  that  he 


AMOUNT   OF   CARBONIC   ACID   EXHALED.  385 

could  eat  and  drink,  read,  or  sleep  within  it.  This  was  connected  with 
an  apparatus,  by  which  the  air  was  continually  renewed ;  and  the  air 
drawn  off  was  carefully  analysed,  in  order  to  determine  the  quantity  of 
carbonic  acid  contained  in  it.  The  average  per  hour,  in  different  states 
having  been  ascertained,  it  was  calculated  that,  allowing  seven  hours 
for  sleep  in  adults,  and  nine  hours  for  children,  the  ^o^a?  *  amount  of 
carbon  consumed  in  the  twenty-four  was  as  follows : — 

No.  Weighing.  Grains.  Oz.  Troy. 

1.  A  male,  aged  thirty-five,  .....  131    lbs.  3387  or  7-0 

2.  A  male,  aged  sixteen, 115J  lbs.  3453  or  7-2 

3.  A  soldier,  aged  twenty-eight,     .     .     .  164    lbs.  3699  or  7-7 

4.  A  girl,  aged  nineteen,  ......  Ill     lbs.  2540  or  6-3 

5.  A  boy,  aged  nearly  ten, 44    lbs.  2054  or  4-3 

6.  A  girl,  aged  ten, 46    lbs.  1930  or  4-0 

695.  This  estimate  is  perhaps  rather  too  low,  as  it  does  not  take 
sufl&cient  account  of  the  great  increase  which  is  produced  by  exercise. 
Another  method  has  been  adopted  by  Prof.  Liebig,  who  endeavoured  to 
ascertain  the  total  amount  of  carbon  excreted  from  the  body  in  the 
form  of  carbonic  acid,  by  comparing  the  amount  of  carbon  taken  in  as 
food,  with  that  contained  in  the  faeces  and  urine ;  the  difference  being 
set  down  to  the  account  of  respiration.  His  estimate  amounts  to  the 
very  large  sum  of  13*9  oz.  of  solid  carbon  per  day,  which  he  considers 
to  be  thus  set  free  by  the  lungs  and  skin ;  but  this  is  almost  certainly 
above  the  truth.  The  observations  were  made  upon  a  body  of  soldiers, 
who  were  subjected  to  severe  daily  exertion;  and  they  were  far  from 
being  exactly  conducted,  many  of  the  items  being  set  down  by  guess 
only,  whilst  of  others  no  account  whatever  was  taken.  We  may  per- 
haps consider  10  or  11  oz.  as  more  nearly  representing  the  amount  of 
carbon  consumed  by  adult  men  exposed  to  severe  exertion ;  whilst  from 
Prof.  Scharling's  experiments  it  may  be  inferred,  that  from  7  to  8  oz. 
of  carbon  are  thrown  off  during  the  twenty-four  hours,  by  the  lungs  and 
skin  of  adult  men  not  using  much  active  exertion ;  to  which  another 
ounce  or  two  may  be  added,  as  the  increased  quantity  excreted  during 
moderate  exercise.  In  a  subsequent  series  of  experiments.  Prof.  Schar- 
ling  ascertained  the  proportion  of  carbonic  acid  given  off  from  the 
general  surface  of  the  human  body,  to  be  from  about  l-30th  to  l-50th 
of  the  whole  amount ;  so  that,  adopting  l-40th  as  the  average,  out  of 
eight  ounces  of  carbon  exhaled,  only  one-fifth  of  in  ounce  is  set  free  in 
the  form  of  carbonic  acid  from  the  Skin. 

696.  If  we  assume  10  oz.  or  4800  grains  of  solid  Carbon,  as  the 
total  amount  excreted  from  the  lungs  and  skin  of  a  male  adult,  using 
active  exercise,  in  the  course  of  twenty-four  hours,  we  find  that  the 
volume  of  carbonic  acid  thus  generated  must  be  nearly  37,000  cubic 
inches,  or  more  than  21  cubic  feet.  Of  this,  about  16  cubic  feet  are 
probably  extricated  from  the  lungs.  But  it  is  probable,  that  about  10 
cubic  feet  per  day  is  nearer  the  ordinary  average.  Now  it  has  been 
ascertained,  that  the  whole  quantity  of  air  which  passes  through  the 
chest  during  that  time  under  similar  circumstances,  is  about  266  cubic 
feet ;  so  that  the  proportion  of  carbonic  acid  contained  in  the  expired 
air  seems  to  average  about  4  per  cent.     It  is  certain,  however,  that 

25 


886  OF   RESPIRATION. 

this  proportion  may  rise  much  higher ;  particularly  when  the  respira- 
tory movements  are  slowly  and  laboriously  performed.  Now  in  order 
that  the  blood  should  be  properly  aerated,  it  is  requisite  that  the  air 
should  contain  no  previous  impregnation  of  carbonic  acid ;  since  the 
diffusion  of  even  a  moderate  percentage  of  that  gas  through  the 
inspired  air,  seriously  impedes  the  exhalation  of  more.  Thus  it  was 
found  by  Messrs.  Allen  and  Pepys,  that,  when  300  cubic  inches  of  air 
were  respired  for  three  minutes,  only  28 J  inches  of  carbonic  acid  (or 
somewhat  more  than  9  per  cent.)  were  present  in  it ;  though  the  rate 
of  its  production  in  a  parallel  experiment,  in  which  fresh  air  was  taken 
in  at  each  inspiration,  was  32  cubic  inches  per  minute,  or  96  cubic 
inches  in  three  minutes.  It  appears  from  the  experiments  of  Dr.  Snow, 
that  the  presence  of  carbonic  acid  in  the  atmosphere  acts  more  delete- 
riously  on  the  system,  in  proportion  as  the  normal  quantity  of  oxygen 
has  been  reduced ;  and  hence,  that  the  substitution  of  carbonic  acid  for 
oxygen  by  the  respiratory  process,  vitiates  the  air  far  more  effectually 
than  the  introduction  of  a  surplus  of  carbonic  acid,  the  normal  quantity 
of  oxygen  being  still  present.  He  concludes  from  his  experiments 
upon  the  lower  animals,  that  5  or  6  per  cent,  of  carbonic  acid  cannot 
exist  in  an  atmosphere  respired  by  Man  without  danger  to  life  ;  and 
that  less  than  half  this  amount  would  soon  be  fatal,  when  it  is  formed 
at  the  expense  of  the  oxygen  of  the  air.  A  still  smaller  proportion  is 
capable  of  producing  very  injurious  results.  Thus  the  discomforts 
occasioned  by  the  presence  of  a  crowded  audience  in  a  church,  lecture- 
room,  or  theatre,  which  is  not  provided  with  sufficient  ventilation,  are 
due  in  great  part  to  the  continued  respiration  of  air,  which  becomes 
loaded  in  the  course  of  an  hour  or  two  with  carbonic  acid  gas,  to  the 
amount  of  from  one-half  to  two  per  cent., — as  has  been  ascertained 
both  by  direct  experiment,  and  by  calculation.  And  there  can  be  no 
reasonable  doubt,  that  the  habitual  respiration  of  such  air,  in  the 
narrow  and  noisome  dwellings  of  the  poor,  or  in  crowded  factories  and 
workshops,  has  a  tendency  to  produce,  both  directly  and  indirectly, 
much  loss  of  physical  and  mental  vigour,  and  also  to  blunt  the  acute- 
ness  of  the  moral  feelings  ;  its  influence  being  specially  noticed  in 
increasing  the  predisposition  to  Epidemic  diseases,  and  in  augmenting 
the  fatality  of  their  attacks. 

697.  The  effects  of  a  simple  deficiency  of  Ox3^gen  in  the  respired  air, 
are  experienced  by  those  who  breathe  a  rarefied  atmosphere,  such  as 
that  which  exists  on  the  summits  of  high  mountains.  All  persons  who 
have  made  such  ascents,  have  experienced  the  insufficiency  of  rarefied 
air  to  sustain  the  degree  of  respiration  required  for  active  exertion. 
As  long  as  the  body  remains  at  rest,  no  inconvenience  is  perceived ; 
but  as  soon  as  the  muscular  system  is  put  into  action,  the  insufficiency 
of  the  supply  of  oxygen  is  manifested  by  the  feeling  of  distress  and 
languor;  which  becomes  so  severe,  that  the  individual,  if  unused  to 
such  ascents,  is  obliged  to  stop  and  take  breath  at  every  few  steps. 
The  necessity  for  doing  so  will  be  easily  understood,  when  it  is  remem- 
bered that  when  the  pressure  of  the  atmosphere  is  reduced  to  half  its 
usual  amount,  the  hulk  of  a  given  weight  of  air  will  be  twice  as  great 
as  at  the  surface  of  the  earth,  or  the  same  measure  will  weigh  only 


CHANGES   EFFECTED   IN   THE   BLOOD.  387 

half  as  much.  Consequently,  when  the  chest  is  completely  filled  with 
air,  the  real  quantity  of  oxygen  included  in  it,  is  only  half  of  that 
which  is  drawn  in  by  a  corresponding  inspiration  at  the  earth's  surface. 

698.  With  regard  to  the  absorption  and  exhalation  of  Nitrogen,  "it 
sterns  probable  that  both  these  processes  are  constantly  going  on ;  but 
that  their  relative  activity  varies  under  different  conditions.  Thus  it 
has  been  ascertained  by  MM.  Regnault  and  Reiset,  that  although 
warm-blooded  animals,  when  subjected  to  their  ordinary  regimen,  usu- 
ally increase  the  amount  of  nitrogen  in  the  atmosphere,  yet  that,  when 
food  is  withheld,  or  the  animals  are  fed  upon  a  diet  to  which  they  are 
unaccustomed,  an  absorption  of  nitrogen  takes  place  ;  this  being  parti- 
cularly remarkable  in  the  hybernating  Mammalia,  in  which  the  gain  in 
weight  by  the  absorption  of  oxygen  and  nitrogen  even  exceeds  the  loss 
occasioned  by  the  exhalation  of  carbon. 

699.  Having  thus  considered  the  changes  produced  by  the  Respira- 
tory function,  in  the  air  submitted  to  it,  we  have  next  to  inquire  into 
converse  series  of  changes  effected  by  it  in  the  blood.  The  nature  of 
these  cannot  be  well  stated  with  precision,  as  they  have  not  yet  been 
fully  determined.  It  was  formerly  supposed,  that  the  venous  blood 
arrives  at  the  lungs  charged  with  carbon,  and  that  this  carbon  is  united 
with  the  oxygen  of  the  air  in  the  lungs  themselves.  Numerous  facts, 
however,  go  to  prove,  that  the  blood  comes  to  the  lungs  charged  with 
carbonic  acid ;  and  that  it  gives  out  this  ready  formed,  and  receives 
oxygen  in  its  stead.  Thus  it  has  been  already  shown,  that  there  is  a 
positive  disappearance  of  oxygen,  more  of  that  element  being  withdrawn 
from  the  atmosphere,  than  is  restored  to  it  in  the  condition  of  carbonic 
acid ;  so  that  we  know  that  the  surplus  must  be  received  into  the  blood. 
Further,  cold-blooded  animals  may  be  made  to  breathe  nitrogen  or 
hydrogen  for  a  sufficient  length  of  time,  to  cause  a  large  quantity  of 
carbonic  acid  to  be  disengaged ;  and  this  must  have  been  brought  to  the 
lungs  ready  formed,  since  no  oxygen  was  present  there  to  generate  it. 
Lastly,  it  can  be  shown  by  experiment,  that  oxygen,  carbonic  acid,  and 
nitrogen  exist  in  a  free  state  in  blood,  arterial  as  well  as  venous ;  but 
that  the  proportion  of  oxygen  is  greater  in  arterial  than  in  venous 
blood,  whilst  that  of  carbonic  acid  is  less.  The  following  table  ex- 
presses the  percentage  of  each  kind  of  gas  in  the  two  sorts  of  blood 
respectively,  as  deduced  from  the  experiments  of  Magnus. 


Carbonic  acid, 

Oxygen, 

Nitrogen, 


Arterial  Blood. 

Venous  Blood. 

62-3 

71-6 

23-2 

15-3 

14-5 

131 

Thus  it  appears  that  the  quantity  of  nitrogen  is  very  nearly  the  same 
in  both,  as  would  be  anticipated  from  what  has  been  already  stated  in 
regard  to  its  non-participation  in  the  respiratory  process ;  whilst  about 
one-third  of  the  free  oxygen  of  arterial  blood  disappears  during  its  cir- 
culation in  the  systemic  capillaries,  to  be  replaced  by  an  equivalent 
amount  of  carbonic  acid ;  and  a  converse  change  takes  place  in  the  pul- 
monary capillaries,  this  additional  portion  of  free  carbonic  acid  being 
set  free,  and  replaced  by  oxygen. 


388  OF  RESPIRATION. 

700.  Thus  it  is  evident,  that  a  part  of  the  change  effected  in  the 
Blood  consists  in  an  alteration  in  the  proportion  of  the  gases  which 
always  exist  in  it,  either  entirely  free,  or  in  a  state  of  such  loose  com- 
bination that  they  can  be  removed  by  the  air-pump.  But  it  may  be 
suspected,  that  a  portion  of  the  effect  consists  in  the  oxidation  of  tlie 
proteine  of  the  fibrinous  constituent ;  since  the  fibrine  of  arterial  blood 
possesses  properties  that  distinguish  it  from  that  of  venous.  It  has 
been  usually  supposed  that  the  hematosine  of  the  red  corpuscles  under- 
goes a  change  under  the  influence  of  oxygen  in  the  lungs,  and  a  con- 
verse change  in  the  systemic  capillaries,  where  it  is  subjected  to  the 
influence  of  carbonic  acid ;  this  change  being  indicated  by  the  altera- 
tion in  the  colour  of  the  red  corpuscles.  The  alteration  in  question, 
however,  seems  due  rather  to  a  physical  than  to  a  chemical  change 
(§  222) ;  and  we  have  no  direct  evidence,  though  much  that  is  indirect, 
of  the  special  influence  of  the  aeration  of  the  blood  upon  the  contents 
of  the  red  corpuscles.  It  appears  tolerably  certain  that  a  part  of  the 
oxygen  imbibed  in  the  lungs,  is  appropriated  to  the  oxidation  of  the 
matters  set  free  by  the  decomposition  of  the  solid  tissues ;  whilst 
another  part  enters  into  combination  with  fatty,  saccharine,  farina- 
ceous, and  other  matters,  existing  in  the  blood  itself,  and  destined  to  be 
carried  off  in  the  form  of  carbonic  acid  and  water,  without  ever  enter- 
ing into  the  composition  of  the  solid  fabric.  The  relative  amounts 
of  carbonic  acid  formed  in  these  two  modes,  vary  in  different  animals 
and  in  different  states  of  the  same  individual :  for  a  man  in  a  warm 
atmosphere,  taking  a  moderate  amount  of  exercise,  may  thus  set  free,  by 
the  waste  of  his  muscular  and  other  tissues,  a  sufficient  quantity  of  carbon 
for  the  maintenance  of  his  animal  heat  by  its  union  with  oxygen ;  but  this 
is  far  from  being  sufficient,  when  a  larger  amount  of  heat  must  be 
evolved,  to  sustain  the  temperature  of  the  body  in  a  colder  climate. 

701.  The  blood  parts  in  the  lungs  with  a  very  large  amount  of  mois- 
ture ;  for  the  inspired  air  is  always  saturated  with  fluid,  as  soon  as  it 
reaches  the  air-cells ;  and,  as  it  is  heated  at  the  same  time  to  about  98°, 
it  thus  receives  a  considerable  addition,  even  if  it  were  previously 
charged  with  as  much  as  it  could  contain  at  a  lower  temperature.  The 
total  quantity  of  fluid  thus  disengaged  will  vary,  therefore,  with  the 
amount  previously  contained  in  the  atmosphere,  being  greater  as  this 
was  less,  and  vice  versd;  but  the  quantity  that  usually  passes  off  seems 
to  be  from  16  to  20  ounces  in  the  twenty-four  hours.  It  cannot  be 
doubted,  that  a  great  part  of  this  water  is  a  simple  exhalation  of  that 
which  has  been  absorbed ;  but,  on  the  other  hand,  it  seems  probable 
that  a  portion  of  it  may  be  actually  formed  in  the  system,  by  the 
union  of  a  portion  of  the  oxygen  absorbed  in  the  lungs,  with  the 
hydrogen  of  the  combustible  matters  of  the  blood.  In  the  various 
forms  of  saccharine  and  farinaceous  aliments,  the  proportion  of  hydrogen 
«,nd  oxygen  are  such  as  would  of  themselves  form  water,  when  the 
-carbon  is  withdrawn ;  but  in  oily  and  fatty  matters,  the  proportion  of 
oxygen  is  far  too  small  thus  to  neutralize  the  hydrogen  ;  and  it  seems 
likely  that  by  their  oxidation  in  the  blood,  as  by  their  combustion  else- 
"where,  water  is  actually  generated  by  the  union  of  atmospheric  oxygen 


ASPHYXIA— ITS   CAUSES.  389 

mth.  their  hydrogen,  at  the  same  time  that  carbonic  acid  is  produced  by 
its  union  with  their  carbon. 

702.  Along  with  the  water  thus  extricated  from  the  lungs,  a  certain 
amount  of  organic  matter  is  set  free.  If  the  fluid  be  collected  in  "a 
closed  vessel,  and  be  exposed  to  warmth,  a  very  evident  putrid  odour 
is  exhaled  from  it ;  and  if  the  expired  air  be  made  to  pass  through 
sulphuric  acid,  that  liquid  is  coloured  red.  Every  one  knows  that  the 
breath  itself  possesses,  occasionally  in  some  persons,  and  constantly  in 
others,  a  foetid  taint ;  when  this  does  not  proceed  from  carious  teeth, 
ulceration  in  the  air-passages  or  lungs,  or  other  similar  causes,  it  must 
result  from  the  excretion  of  the  odorous  matter,  in  combination  with 
watery  vapour,  from  the  pulmonary  surface.  That  this  is  the  true 
account  of  it  seems  evident,  from  the  analogous  phenomenon  of  the 
exhalation  of  turpentine,  camphor,  alcohol,  and  other  odorous  sub- 
stances, which  have  been  introduced  into  the  venous  system,  either  by 
natural  absorption,  or  by  direct  injection ;  and  also  from  the  sudden- 
ness with  which  the  odour  manifests  itself,  when  the  digestive  appa- 
ratus is  slightly  disordered. 

5.  Effects  of  Insufficiency  J  or  Suspension^  of  the  Aerating  Process. 

703.  The  change  which  the  Blood  undergoes,  by  being  brought  into 
relation  with  atmospheric  air  in  the  respiratory  organs,  is  so  important 
to  life,  that  the  entire  suspension  of  it  inevitably  produces  a  fatal  ter- 
mination, at  no  remote  period ;  and  if  it  be  insufficiently  performed, 
various  disorders  in  the  system  are  nearly  sure  to  manifest  themselves. 
The  state  which  is  induced  by  the  entire  suspension  of  the  aerating 
process,  is  termed  Asphyxia ;  a  word  which  literally  means  the  absence 
of  pulse,  and  would  be  applicable  therefore  to  the  stoppage  of  the  cir- 
culation from  any  cause ;  though  it  is  usually  employed  to  designate 
the  particular  condition  resulting  from  suspended  respiration.  Asphyxia 
may  be  produced  in  aquatic  animals,  as  well  as  in  those  which  breathe  air, 
by  cutting  them  off  from  the  influence  of  the  atmosphere  ;  for  if  a  fish 
be  placed  in  water  from  which  the  air  has  been  expelled  by  boiling,  it  is 
precisely  in  the  condition  of  an  air-breathing  animal  placed  in  a  vacuum, 
since  it  has  no  power  of  obtaining  oxygen  by  decomposing  the  water  it 
inhabits,  and  is  entirely  dependent  for  the  aeration  of  its  blood,  upon 
the  air  that  is  absorbed  by  the  liquid.  Again,  if  a  fish  be  placed  in 
water  impregnated  with  carbonic  acid,  its  death  is  nearly  as  instan- 
taneous as  that  of  an  air-breathing  animal  immersed  in  an  atmosphere 
of  that  gas. 

704.  Asphyxia  may  result  from  a  great  variety  of  causes.  Thus  there 
may  be  a  mechanical  obstruction  to  the  entrance  of  air  through  the 
trachea ;  as  in  hanging,  strangulation,  or  drowning ;  or  as  in  occlusion 
of  the.  aperture  of  the  glottis,  by  oedema  of  its  lips,  or  by  the  presence 
of  a  foreign  body  in  the  larynx.  Or,  again,  the  passage  may  be  perfectly 
free,  and  yet  no  air  may  enter,  in  consequence  of  some  obstacle  to  the 
performance  of  the  respiratory  movements.  This  obstacle  may  be  me- 
chanical; as  when  a  quantity  of  earth  has  fallen  round  the  body,  in  such  a 
manner  as  completely  to  prevent  the  distension  of  the  chest  and  abdomen. 
Or  it  may  result  (and  this  is  a  most  frequent  occurrence)  from  torpidity 


390  OF   RESPIRATION. 

or  complete  inactivity  of  the  ganglionic  centre,  whicli  is  concerned  in 
the  respiratory  actions ;  or  from  interruption  to  the  transmission  of  its 
influence  along  the  nervous  trunks.  Further,  when  there  is  no  obstacle 
to  the  free  ingress  or  egress  of  air,  Asphyxia  may  be  produced  by  the  want 
of  oxygen  in  the  atmosphere  that  is  respired,  or  by  the  presence  of  car- 
bonic acid  in  too  large  an  amount.  And  the  presence  of  other  gases, 
which  exert  a  directly  poisonous  influence  on  the  blood, — such  as  sulphu- 
retted hydrogen, — produces  a  state,  which  may  be  included  under  the 
same  general  description. 

705.  Now  when,  from  any  of  these  causes,  the  free  exchange  of  car- 
bonic acid  for  oxygen  in  the  pulmonary  capillaries  is  checked,  the  first 
effect  of  the  interruption  appears  to  be,  the  stagnation  of  the  blood  in 
the  pulmonary  capillaries.     This  stagnation  is  evidently  due,  not  to  any 

"  deficiency  of  power  in  the  heart ;  for  that  organ  is  not  yet  affected  ;  but 
to  the  insufficiency  of  the  heart's  power,  acting  alone,  to  drive  the  blood 
through  the  pulmonary  capillaries  :  the  force  which  should  be  generated 
by  chemical  changes  in  them  (§  598),  being  deficient.  The  stagnation 
is  not,  however,  complete  at  first ;  since  the  quantity  of  oxygen  contained 
in  the  lungs  is  sufficient  to  produce  an  imperfect  arterialization  of  the 
blood  ;  and  the  blood  thus  partially  changed  is  transmitted  to  the  left 
side  of  the  heart,  and  is  thence  propelled  to  the  system.  Owing  to  its 
half-venous  condition,  it  cannot  exert  its  usual  stimulating  influence  on 
the  tissues,  especially  the  muscular  and  nervous ;  and  their  powers  are 
consequently  weakened.  For  the  same  reason,  it  does  not  receive  its 
usual  auxiliary  force  in  the  systemic  capillaries  (§  599) ;  since  the 
changes,  which  it  ought  to  undergo  in  them,  can  only  be  partially  per- 
formed. 

706.  As  the  air  included  in  the  lungs  loses  more  and  more  of  its  oxy- 
gen, and  becomes  more  and  more  charged  with  carbonic  acid,  the  aeration 
of  the  blood  in  the  pulmonary  capillaries  becomes  more  and  more  im- 
perfect ;  the  quantity  of  blood  which  is  allowed  to  return  to  the  heart  is 
gradually  diminished,  and  its  condition  becomes  more  and  more  venous ; 
and  at  last,  the  pulmonary  circulation  is  altogether  suspended.  From 
the  relation  which  the  respiratory  circulation  bears  to  the  systemic,  in 
all  the  higher  classes  of  animals,  save  Reptiles,  it  follows  that  the  sys- 
temic circulation  must  in  like  manner  be  brought  to  a  stand.  The  venous 
blood  accumulates  in  the  pulmonary  artery,  in  consequence  of  the  ob- 
struction of  its  capillaries ;  it  distends  the  right  cavities  of  the  heart ; 
and  the  accumulation  extends  to  the  venous  system  of  the  body  in 
general,  especially  affecting  those  organs  which  naturally  receive  a  large 
quantity  of  venous  blood,  such  as  the  liver  and  spleen.  The  arterial 
system,  on  the  other  hand,  is  emptied  in  a  corresponding  degree;  nearly 
all  its  blood  having  passed  through  the  systemic  capillaries ;  and  no 
fresh  supplies  being  received  from  the  heart.  From  this  deficiency, 
and  from  the  venous  character  of  the  blood  which  the  systemic  arteries 
do  contain,  it  results  that  the  nervous  and  muscular  systems  lose  their 
power ;  insensibility  comes  on,  at  first  accompaniea  with  irregular  con- 
vulsive movements ;  but  in  a  short  time  there  is  a  total  cessation  of  all 
movement  except  that  of  the  heart ;  and  the  pulsations  of  that  organ  be- 
come feebler  and  feebler,  until  they  cease  altogether.  The  immediate 
cause  of  the  cessation  of  the  heart's  action  appears  to  be  different  on  the 


ASPHYXIA — ITS   PHENOMENA   AND   TREATMENT.  391 


»- 


0  sides.  Both  are  equally  affected  by  the  want  of  arterial  blood  in  the 
capillaries  of  their  own  substance ;  but  the  right  side  suffers  from  over 
distension,  which  produces  a  sort  of  paralysis  of  its  muscular  tissue ; 
whilst  the  left  side  retains  its  contractility,  but  is  not  excited  to  con^ 
traction,  for  want  of  the  stimulus  of  arterial  blood  in  its  cavities. 

707.  In  those  warm-blooded  animals  which  are  not  endowed  with 
any  special  provision  for  enabling  them  to  sustain  life  during  the  pro- 
longed suspension  of  the  respiratory  process,  insensibility  and  loss  of 
voluntary  power  almost  invariably  supervene  within  a  minute  and  a 
half  after  the  admission  of  air  to  the  lungs  has  been   entirely  pre- 
vented;  though  the  respiratory  efforts  and  convulsive  actions,  which 
are  dependent  upon  the  medulla  oblongata  and  spinal  cord,  may  con- 
tinue for  a  minute  or  two  longer.     The  circulation  generally  comes  to 
a  complete  stand  within  ten  minutes  at  farthest. — The  chief  exceptions 
are  in  the  case  of  diving  animals,  which  are  provided  with  large  arterial 
and  venous  reservoirs,  that  serve  to  maintain  the  circulation  during 
a  prolonged  suspension  of  the  respiratory  process ;  for  the  arterial 
plexuses  being  ordinarily  filled,  they  afford  a  supply  of  aerated  blood 
to  the  systemic  capillaries,  when  other  blood  is  wanting ;  and  the  reser- 
voirs connected  with  the  venous  system,  which  were  previously  empty, 
receive  this  blood,  and  prevent  it  from  exercising  undue  pressure  on 
the  heart.     To  such  an  extent  is  this  provision  carried  in  some  ani- 
mals, that  the  Whale  has  been  known  to  remain  under  water  for  an 
hour.     Another  exception  exists  in  the  case  of  hybernating  Mammals, 
which  are  reduced  for  a  time  to  the  condition  of  cold-blooded  animals, 
and  which  can,  like  the  latter,  sustain  a  prolonged  suspension  of  the 
aerating  process.     And  there  is  reason  to  believe  that,  in  the  state  of 
Syncope  or  fainting, — in  which  the  circulation  is  already  reduced  to  a 
very  low  amount,  in  consequence  of  a  partial  failure  in  the  heart's 
power,  all  the  functions  of  the  body  being  nearly  suspended,  and  the 
demand  for  aeration  being  consequently  very  small, — the  respiration 
may  be  suspended  for  a  long  period,  even  in  the  Human  subject,  with- 
out fatal  results.     Thus  more  than  one  case  has  been  credibly  recorded, 
in  which  recovery  has  taken  place  after  complete  submersion  for  more 
than  three  quarters  of  an  hour ;  and  it  is  probable  that,  in  these  in- 
stances,  a  state  of  Syncope  came  on  at  the  moment  of  immersion, 
through  the  influence  of  mental  emotion,  or  of  concussion  of  the  brain. 
708.  In  the  restoration  of  an  animal  from  the  state  of  Asphyxia, 
it  is  above  all  things  of  importance  to  renew  the  air  in  the  lungs  ;  for 
in  this  way  the  blood  in  the  pulmonary  capillaries  will  be  aerated,  the 
capillary  circulation  will  be  re-established,  the  right  side  of  the  heart 
will  be  relieved  of  its  excessive  load  of  venous  blood,  and  the  left  side 
will  receive  the  stimulus  of  a  fresh  supply  of  arterial  blood  ;  so  that, 
if  its  movements  have  not  ceased  altogether,  it  may  be  speedily  restored 
to  due  activity.     At  the  same  time,  the  temperature  of  the  body  should 
be  kept  up  by  artificial  warmth  ;  and  the  circulation  in  the  skin  should 
be  excited  by  friction.     Where  no  other  means  are'  at  hand  for  intro- 
ducing pure  air  into  the  lungs  (of  which  means  the  application  of  gal- 
vanism along  the  course  of  the  phrenic  nerve,  so  as  to  produce  contrac- 
tion of  the  diaphragm,  will  probably  be  the  most  effectual),  the  object  may 


392  OF   RESPIRATION. 

be  attained  by  forcibly  compressing  the  trunk  on  all  sides,  so  as  to  empty 
the  lungs  as  much  as  possible,  and  then  allowing  the  chest  to  dilate 
again,  by  the  elasticity  of  its  walls.  In  this  manner,  a  large  proportion 
of  the  carbonic  acid  may  be  expelled,  and  a  considerable  proportion  of 
fresh  air  introduced,  in  the  course  of  a  few  minutes.  If  air  be  blown 
into  the  lungs  by  the  bellows,  great  care  must  be  taken  to  prevent  the 
employment  of  too  much  force,  which  is  likely  to  produce  rupture  of 
the  air-cells. 

709.  Now  when,  from  the  more  prolonged  action  of  various  causes 
that  impede  the  due  performance  of  the  respiratory  function,  the  aera- 
tion of  the  blood  in  the  lungs  is  insufficient  for  health,  though  not  such 
as  to  produce  a  complete  stagnation  of  the  movement,  a  variety  of 
results  may  follow ;  of  which  some,  or  others,  will  manifest  themselves, 
according  to  the  condition  of  the  general  system,  and  the  peculiarities 
of  the  individual.  Thus  deficient  respiration  seems  to  favour  the  re- 
tention of  fatty  matter  in  the  system ;  and  this  not  merely  in  the  con- 
dition of  Adipose  tissue,  which  (unless  it  accumulate  to  excess)  may  be 
regarded  as  a  healthy  product ;  but  also  in  the  place  of  the  normal 
components  of  other  tissues,  as  the  muscular  and  glandular,  giving  rise 
to  the  condition  which  is  termed  "  fatty  degeneration." — Again,  the 
due  elaboration  of  the  fibrin e  of  the  blood  is  undoubtedly  prevented  by 
an  habitually-deficient  respiration ;  and  various  diseases,  which  result 
from  the  imperfect  performance  of  this  elaboration,  consequently  mani- 
fest themselves.  The  Scrofulous  diathesis  is  thus  frequently  connected 
with  an  unusually  small  capacity  of  the  chest. — Further,  an  habitual 
deficiency  of  respiration  may  impede,  though  it  does  not  check,  the  cir- 
culation in  the  lungs ;  and  thus  a  tendency  arises,  in  various  pulmonary 
diseases,  to  an  overloading  of  the  pulmonary  arteries,  to  a  dilatation  of 
the  right  cavities  of  the  heart,  and  to  a  congestion  of  the  venous 
system  in  general,  as  marked  by  lividity  of  the  surface,  by  venous  pul- 
sation, &c.  This  state  may  result,  not  merely  from  obstruction  in  the 
lungs  themselves,  but  from  deficiency  of  the  respiratory  movements, 
consequent  upon  torpidity  of  the  medulla  oblongata  (as  in  apoplexy 
and  narcotic  poisoning),  or  upon  partial  interruption  of  the  nervous 
circle  requisite  for  all  reflex  movements.  Thus  when  the  par  vagum  is 
divided,  the  number  of  respiratory  movements  is  greatly  diminished, 
and  a  partial  stagnation  of  the  blood  in  the  lungs  is  the  result.  The 
same  happens  in  certain  forms  of  typhoid  fever,  in  which  the  respi- 
ratory movements  are  preternaturally  slow,  in  consequence  of  torpidity 
of  the  medulla  oblongata.  Now  in  this  state,  an  efiusion  of  the  watery 
part  of  the  blood  into  the  air-cells  of  the  lungs  (as  in  other  cases  of 
obstructed  circulation)  is  very  liable  to  occur ;  and  when  the  lungs  are 
thus  loaded  with  fluid,  the  respiratory  process  is  still  more  impeded, 
and  the  disorder  has  thus  a  tendency  to  increase  itself. 


t 


NATURE   OF   THE   SECEETING   PROCESS.  393 

CHAPTER  IX. 

OF  SECRETION. 

1.   Of  the  secreting  process  in  general ;  and  of  the  instruments  hy  which 

it  is  effected. 

710.  We  have  seen  that,  in  the  process  of  Nutrition,  the  circulating 
current  not  only  deposits  the  materials,  which  are  required  for  the 
renovation  of  the  solid  tissues;  but  also  takes  back  the  substances, 
which  are  produced  by  the  decay  of  these,  and  which  are  destined  to 
be  thrown  off  from  the  body.  We  have  also  seen,  that  it  supplies  the 
materials  of  certain  fluids,  which  are  separated  from  it  to  effect  various 
purposes  in  the  economy;  such  as  the  Salivary  and  Gastric  fluids,  which 
have  for  their  office  to  assist  in  the  reduction  of  the  food.  Now  the 
process  bjL  which  the  fluids  of  the  latter  kind  are  separated  from  the 
Blood,  is  precisely  the  same  in  character  as  that  by  which  the  products 
of  decay  are  eliminated  from  it ;  and  the  structure  of  the  organs  con- 
cerned in  the  two  is  essentially  the  same.  Hence  both  processes  are 
commonly  included  under  th«  general  term  Secretion,  which  simply 
denotes  separation.  Considered  in  its  most  general  point  of  view,  this 
designation  may  be  applied  to  every  act,  by  which  substances  of  any 
kind  are  separated  from  the  blood.  Thus  the  function  of  the  cells, 
which  are  concerned  in  the  elaboration  of  the  organizable  plasma,  may 
be  termed  one  of  Secretion,  because  they  draw  from  the  blood  a  supply 
of  Albumen,  upon  which  their  converting  action  is  exercised ;  but  as 
the  product  of  their  operation  is  returned  to  the  blood  again,  and  is 
employed  for  higher  purposes  in  the  economy,  the  process  is  usually 
termed  Assimilation.  In  the  same  manner,  the  elaborating  action  of 
the  Lymphatic  Glands,  with  the  Spleen,  Thymus  Gland,  &c.,  is  not 
usually  termed  Secretion ;  since,  although  it  is  exercised  upon  matter 
drawn  from  the  blood,  the  product  appears  to  be  delivered  back  into 
the  circulating  current,  through  the  medium  of  the  Lymphatic  System. 
(chap,  v.)  With  much  more  justice,  however,  the  process  of  Respira- 
tion may  be  regarded  as  one  of  Secretion ;  for  it  consists,  as  we  have 
seen,  in  the  constant  elimination  of  a  substance  from  the  blood,  which 
cannot  be  retained  in  it  without  the  most  injurious  consequences. 

711.  There  is  an  important  difference  in  the  characters  of  the  prin- 
cipal products  of  the  Secreting  process,  which  is  connected  with  the 
purposes  that  are  to  be  answered  by  their  separation.  Some  of  these 
products  are  altogether  different  from  the  ordinary  constituents  of  the 
animal  fabric,  and  from  the  materials  which  the  blood  supplies  for  the 
nutrition  of  these.  So  different  are  they,  that  their  presence  in  the 
circulating  current  has  an  injurious  effect ;  and  the  great  object  of  their 
separation  is  the  maintenance  of  the  purity  of  the  blood.  These  poi- 
sons, for  such  they  may  be  considered,  are  generated  in  the  system  by 
the  decay  and  decomposition  to  which  its  several  parts  are  liable ;  and 

;hey  are  just  as  noxious  to  it,  as  if  they  were  absorbed  from  without. 


394  OF   SECKETION. 

We  have  seen  that  the  retention  of  Carbonic  acid  in  the  blood  for  even 
a  few  minutes  is  fatal,  both  by  putting  a  stop  to  the  circulation,  and 
by  acting  unfavourably  upon  the  substance  of  some  of  the  most  impor- 
tant organs  in  the  body.  The  same  fatal  result  attends  the  retention  of 
Urea  and  of  Biliary  matter,  which  are  among  the  other  products  of  the 
decomposition  of  the  tissues;  but,  although  as  certain,  it  is  not  so 
speedy,  because  the  general  circulation  is  not  affected  by  the  loss  of 
secreting  power  on  the  part  of  the  Kidneys  and  the  Liver,  and  because 
the  accumulation  of  the  noxious  matter  is  slower. — On  the  other  hand, 
the  ingredients  that  are  met  with  in  those  secreted  fluids,  which  are 
destined  to  answer  some  purpose  in  the  economy,  almost  invariably 
bear  a  close  correspondence  with  the  ordinary  materials  of  the  blood. 
Thus  in  the  Salivary,  Gastric,  Pancreatic,  and  Lachrymal  fluids,  the 
principal  part  of  the  solid  matter  consists  of  the  saline  and  of  the  albu- 
minous constituents  of  the  blood,  the  latter  in  a  more  or  less  altered 
condition.  In  Milk,  again,  we  trace  the  ordinary  constituents  of  the 
blood,  with  very  little  change.  Thus  it  appears,  that  the  separation  of 
these  fluids  is  not  required  so  much  to  maintain  the  Blood  in  a  state  of 
purity,  as  to  supply  what  is  needed  for  some  subsequent  operation  in 
the  economy ;  and  hence,  if  the  secreting  process  be  interrupted,  in  the 
case  of  any  one  of  them,  the  suspension  has  usually  no  further  effect, 
than  that  of  disturbing  the  process  to  which  the  fluid  is  usually  subser- 
vient. If  the  secretion  of  Gastric  fluid  be  checked,  for  example,  under 
the  influence  of  strong  mental  emotion,  the  Digestive  operation  is  pre- 
vented from  taking  place. 

712.  The  essential  character  of  the  true  Secreting  operation  seems 
to  consist, — not  in  the  nature  of  the  action  itself,  for  this  is  identical 
with  those  of  Assimilation  and  Nutrition,  being,  as  we  have  seen  (§  239), 
a  process  of  cell-growth, — but  in  the  position  in  which  the  cells  are 
developed,  and  the  mode  in  which  the  products  of  their  action  are 
afterwards  disposed  of.  Thus  the  cells  at  the  extremities  of  the  intes- 
tinal Villi  (§  243),  the  cells  of  which  the  Adipose  tissue  is  made  up 
(§  257),  and  the  cells  of  which  the  greater  part  of  the  substance  of  the 
Liver  is  formed  (§  239),  all  have  an  attraction  for  fatty  matter ;  and 
draw  it  from  the  neighbouring  fluids,  at  the  expense  of  which  they  are 
developed,  to  store  it  up  in  their  own  cavities.  But  the  cells  of  the 
first  kind,  when  they  have  come  to  maturity,  set  free  their  contents, 
which  are  delivel-ed  to  the  absorbent  vessels,  to  be  introduced  into  the 
circulating  current ; — those  of  the  second  kind  seem  more  permanent 
in  their  character,  and  retain  their  contents,  so  as  to  form  part  of  the 
ordinary  tissues  of  the  body,  until  they  are  required  to  give  them  up 
for  other  purposes,  when  the  matters  which  they  have  temporarily 
separated  from  the  circulating  current,  are  restored  to  it  again  without 
change ; — and  the  cells  of  the  third  class,  when  they  liberate  their  con- 
tents (which  they  are  continually  doing),  cast  them  forth  into  the 
hepatic  ducts,  by  which  they  are  carried  into  the  intestinal  canal, 
whence  a  portion  of  them  at  least  is  directly  conveyed  out  of  the  hod^y. 

713.  It  is,  then,  in  the  position  of  the  Secreting  cells, — which  causes 
the  product  of  their  action  to  be  delivered  upon  a/ree  surface^  commu- 
nicating, more  or  less  directly,  with  an  external   outlet, — that   their 


SIMPLEST  FORM   OP  GLANDULAR   STRUCTURE.  395 

distinctive  character  depends.  All  the  proper  Secretions  are  thus  either 
poured  out  upon  the  exterior  of  the  body,  or  into  cavities  provided 
with  orifices  that  lead  to  it.  Thus  we  shall  see  that  a  considerable 
quantity  of  solid  matter,  and  a  very  large  quantity  of  fluid,  of  which 
it  is  desirable  that  the  system  should  be  freed,  are  carried  off  from  the 
Cutaneous  surface.  Another  most  important  secretion,  containing  a 
large  quantity  of  solid  matter,  and  serving  also  to  regulate  the  quan- 
tity of  fluid  in  the  body, — namely,  the  Urinary, — is  set  free  by  a 
channel  expressly  adapted  to  convey  it  directly  out  of  the  body.  The 
same  may  be  said  of  the  Mammary  Secretion,  which  is  separated  from 
the  blood,  not  to  preserve  its  purity,  nor  to  answer  any  purpose  in  the 
economy  of  the  individual,  but  to  aff'ord  nutriment  to  another  being. 
And  of  the  matters  secreted  by  the  very  numerous  glandulae  situated 
in  the  walls  of  the  Intestinal  canal,  a  great  part  are  obviously  poured 
~  ito  it  for  no  other  purpose,  than  that  they  may  be  carried  out  of  the 
)ody  by  the  readiest  channel. 

714.  The  cells  covering  the  simple  membranes  that  form  the  free 
mrfaces  of  the  body,  whether  external  or  internal,  are  all  entitled  to 
)e  regarded  as  secreting  cells,  since  they  separate  various  products 
From  the  blood,  which  are  not  again  to  be  returned  to  it.  But  the 
jecreting  action  of  some  of  these  seems  to  have  for  its  object  the  pro-. 

hection  of  the  surface ;  thus  the  Epidermic  cells  secrete  a  horny  matter, 
~)y  which  density  and  firmness  are  imparted  to  the  cuticle ;  whilst  by 
^he  epithelial  cells  of  the  Mucous  membrane  of  the  alimentary  canal, 
ind  of  other  parts,  their  protective  Mucus  seems  to  be  elaborated. 
~»ut  in  general  we  find  that  special  organs,  termed  Grlands,  are  set 
ipart  for  the  production  of  the  chief  secretions ;  and  we  have  now  to 
consider  the  essential  structure  of  these  organs,  and  the  mode  of  their 
operation. — A  true  Gland  may  be  said  to  consist  of  a  closely-packed 
collection  of  follicles,  all  of  which  open  into  a  common  channel,  by 
which  the  product  of  the  glandular  action  is  collected  and  delivered. 
The  follicles  contain  the  secreting  cells  in  their  cavities  ;  whilst  their 
exterior  is  in  contact  w^ith  a  network  of  blood-vessels,  from  which  the 
cells  draw  the  materials  of  their  growth  and  development  (Fig.  94). 
In  any  one  of  the  higher  animals,  we  may  trace  out  a  series  of  pro- 
gressive stages  of  complexity,  in  the  various  glands  included  within 
their  fabric ;  and  in  following  any  one  of  the  glands  that  attain  the 
highest  degree  of  development  (such  as  the  Liver  or  Kidney),  through 
the  ascending  scale  of  the  Animal  series,  we  should  trace  a  very  similar 
gradation  from  the  simplest  to  the  most  complex  form. 

715.  That  there  is  nothing  in  the  form  or  disposition  of  the  compo- 
lents  of  the  glandular  structure,  which  can  have  any  influence  upon 

^the  character  of  the  secretion  it  elaborates,  is  evident  from  the  fact, 
"that  the  very  same  product, — e.g.,  the  Bile,  or  the  Urine, — is  found 
bo  issue  from  nearly  every  variety  of  secreting  structure,  as  we  trace 
it  through  the  diff'erent  groups  of  the  Animal  kingdom.  The  peculiar 
)ower  by  which  one  organ  separates  from  the  Blood  the  elements  of 
fehe  Bile,  and  another  the  elements  of  the  Urine,  whilst  a  third  merely 
seems  to  draw  off"  a  certain  amount  of  its  albuminous  and  saline  con- 
stituents, is  obviously  the  attribute   of  the   ultimate  secreting   cells, 


396 


OF  SECRETION. 


which  are  the  real  agents  in  the  secreting  process  (§  239).  Why  one 
set  of  cells  should  secrete  Bile,  another  Urea,  and  so  on,  we  do  not 
know ;  but  we  are  equally  ignorant  of  the  reason,  for  which  one  set 
of  cells  converts  itself  into  Bone,  another  into  Muscle,  and  so  on. 
This  variety  in  the  endowments  of  the  cells,  by  whose  aggregation 
and  conversion  the  fabric  of  the  higher  Animals  is  made  up,  is  a  fact 
which  we  cannot  explain,  and  which  must  be  regarded  (for  the  present, 
at  least,)  as  one  of  the  "ultimate  facts"  of  Physiological  Science. 

716.  Passing  by  the  extended  membranous  surfaces,  and  the  protec- 
tive cells  with  which  they  are  covered,  we  find  that  the  simplest  form 
of  a  secreting  organ  is  composed  of  an  inversion  of  that  surface  into  a 
series  of  follicles,  which  discharge  their  contents  upon  it  by  separate 
orifices.  Of  this  we  have  an  example  in  the  gastric  follicles,  even  in 
the  higher  animals ;  the  apparatus  for  the  secretion  of  the  Gastric  fluid 
never  attaining  any  higher  condition,  than  that  of  a  series  of  distinct 
follicles,  lodged  in  the  walls  of  the  stomach,  and  pouring  their  products 
into  its  cavity  by  separate  apertures.  In  Fig.  107  is  represented  a 
portion  of  the  Ventriculus  succenturiatus  of  a  Falcon ;  in  which  the 
simplest  form  of  such  follicles  is  seen.  A  somewhat  more  complex 
condition  is  seen  in  some  of  the  Gastric  follicles  of  the  Human  stomach 
(Fig.  80) ;  the  surface  of  each  follicle  being  further  extended  by  a  sort 
of  doubling  upon  itself,  so  as  to  form  the  commencement  of  secondary 
follicles,  which  open  out  of  the  cavity  of  the  primary  one. — Now  a  con- 
dition of  this  kind  is  common  to  all  glands,  in  an  early  stage  of  their 
evolution  ;  and  in  this  stage,  we  meet  with  them,  either  by  examining 
them  in  the  lowest  animals  in  which  they  present  themselves,  or  by 
looking  to  an  early  period  of  their  embryonic  development  in  the 
highest.  Thus,  for  example,  the  Liver  consists,  in  certain  Polypes  and 
in  the  lowest  Mollusca,  of  a  series  of  isolated  follicles,  lodged  in  the 
walls  of  the  stomach,  and  pouring  their  product  into  its  cavity  by  sepa- 
rate orifices ;  these  follicles  being  recognised  as  constituting  a  biliary 
apparatus,  by  the  colour  of  their  secretion.      And  in  the  Chick,  at  an 


Fig.  107. 


Fig.  108. 


Glandular  follicles  in  ventriculuB 
succenturiatus  of  Falcon. 


Origin  of  the  liiver  from  the  intestinal  wall,  in 
the  embryo  of  the  Fowl,  on  the  fourth  day  of  in- 
cubation:— a,  heart;  b,  intestine;  c,  everted  por- 
tion giving  origin  to  liver;  d,  liver;  e,  portion  of 
yolk-bag. 


early  period  of  incubation,  the  condition  of  the  Liver  is  essentially  the 
same  with  the  preceding;  for  it  consists  of  a  cluster  of  isolated  follicles, 
not  lodged  in  the  walls  of  the  intestine,  but  clustered  round  a  sort  of 


DIFFERENT   FORMS    OF   GLANDULAR   STRUCTURE. 


39T 


bud  or  diverticulum  of  the  intestinal  tube,  which  is  the  first  condition 
of  the  hepatic  duct,  and  into  which  they  discharge  themselves  (Fig. 
108).     So,  again,  the  Pancreas  first  presents  itself  in  the  condition  of 


Fig.  109. 


Fig.  110. 


Rudimentary  Pancreas  from  Cod : — a, 
pyloric  extremity  of  stomach ;  b,  intes- 
tine. 


Mammary  Gland  of  Ornithorhyncus. 


a  group  of  prolonged  follicles,  or  cceca,  clustered  round  the  commence- 
ment of  the  intestinal  tube ;  and  this  is  its  permanent  condition  in  many 
Fishes  (Fig.  109).  And  the  Mammary  Gland  possesses  an  equally 
simple  structure  in  the  lowest  of  all  the  Mammalia  (to  which  group  it  is 
restricted) ;  namely,  in  the  Ornithorhyncus  (Fig.  110). 

717.  The  next  grade  of  complexity  is  seen,  where  a  cluster  of  the 
ultimate  follicles  open  into  one  common  duct,  which  discharges  their 
product  by  a  single  outlet ;  a  single  gland  often  containing  a  number  of 
such  clusters,  and  having,  therefore,  several  excretory  ducts.  A  good 
example  of  such  a  condition,  in  which  the  clusters  remain  isolated 
from  one  another,  is  seen  in  the  Meibomian  glands  of  the  eyelid 
(Fig.  Ill) ;  each  of  which  consists  of  a  double  row  of  follicles,  set  upon 
a  long  straight  duct,  that  receives  the  products  of  their  secreting  action 


Fig.  111. 


Fig.  112. 


Meibomian  glands  of  upper  lid  of 
new-born  infant. 


Portion  of  Cowper's  gland  from  Hedgehog;  the 
follicles  distended  with  air. 


and  pours  them  out  upon  the  edge  of  the  eyelid.     And  of  the  more 
complex  form,  in  which  a  number  of  such  clusters  are  bound  together 


398 


OF   SECRETION. 


in  one  glandular  mass,  we  have  an  illustration  in  the  accessory  glands 
of  the  genital  apparatus,  in  several  animals,  which  discharge  their 
secretion  into  the  urethra  by  numerous  outlets  (Fig.  112) ;  or  in  the 
Mammary  glands  of  Mammalia  in  general,  the  ultimate  follicles  of 
which  are  clustered  upon  ducts  that  coalesce  to  a  considerable  extent 
though  continuing  to  form  several  distinct  trunks  even  to  their  termi- 
nation.    Such  glands  may  be  subdivided,  therefore,  into  glandulce  or 

Fig.  113. 


Lobule  of  Lachrymal  Gland ;  from  foetal  sheep. 

lobules,  that  remain  entirely  distinct  from  each  other  (Fig.  113). — In 
the  highest  form  of  Gland,  however,  all  the  ducts  unite ;  so  as  to  form  a 
single  canal,  which  conveys  away  the  products  of  the  secreting  action 
of  the  entire  mass.  This  is  the  condition  in  which  we  find  the  Liver 
to  exist,  in  most  of  the  higher  animals ;  also  the  Pancreas,  the  Parotid 
Gland,  and  many  others.  In  some  of  these  cases,  we  may  still  sepa- 
rate the  gland  into  numerous  distinct  lobules,  which  are  clustered  upon 
the  excretory  duct  and  its  branches,  like  grapes  upon  a  stalk ;  in  others, 
however,  the  branches  of  the  excretory  duct  do  not  confine  themselves 
to  ramifying,  but  inosculate,  so  as  to  form  a  network,  which  passes 
through  the  whole  substance  of  the  gland,  and  which  connects  together 
its  different  parts,  so  as  to  render  the  division  into  lobules  less  distinct. 
This  seems  to  be  the  case  in  regard  to  the  Liver  of  the  higher  Verte- 
brata  (§  723). 

718.  Whatever  degree  of  complexity,  however,  prevails  in  the  gene- 
ral arrangement  of  the  elements  of  the  Glands  in  higher  animals,  these 


Fig.  114. 


Fig.  115. 


Two  follicles  from  the  liver  of  Carcinus  mcmas  (Com- 
mon Crab),  with  their  eontained  secreting  cells. 


Ultimate  follicles  of  Mammary  gland  with  their 
secreting  cells,  a,  a  ;—b,  b,  the  nuclei. 


elements  are  themselves  everywhere  the  same ;  consisting  of  follicles 
that  enclose  the  .real  secreting  cells  (Figs.  114  and  115).     Now  from 


DIFFERENT  FORMS   OF   GLANDULAR   STRUCTURE. 

le  history  of  the  development  of  Glands  in  general,  it  appears  that  the 
follicles  may  be  considered   as  parent-cells  and  that  the  secreting  cells 
the  interior   constitute  a  second   generation,    developed  from  the 
luclei  germinal  spots  on  the  walls  of  the  first.     Of  such  parent-cells,  we 
lave  characteristic  examples  in  the  Peyerian  glandulse  of  the  intestinal 
mal  (§  450),  and  also  in  the  Thyroid  gland  (§  513)  and  Supra-Renal 
Capsules  (§  510) ;  and  the  most  elaborate  glands,  in  their  earliest  stage 
)f  development,  present  a  similar  condition.     These  closed  cells  become 
follicles,  by  opening  at  one  extremity,  either  upon  a  neighbouring  free 
mrface,  or  into  a  canal  which  is  prolonged  from  it.     Thus  the  first  rudi- 
lent  of  the  Liver  is  formed  by  a  thickening  of  the  cellular  mass  in  the 
rails  of  the  alimentary  canal,  at  the  spot  in   which  the  hepatic  duct 
subsequently  to  discharge  itself.     This  thickening  increases,  so  as 
form  a  projection  upon  the  exterior  of  the  canal ;  and  soon  after- 
rards  the  lining  membrane  dips  down  into  it,  so  that  a  kind  of  caecum 
formed,  surrounded  by  a  mass  of  cells,  as  shown  in  Fig.  108.     The 
icrease  of  the  mass  seems  to  take  place  by  a  continual  new  budding- 
>rth  of  cells  from  its  peripheral  portion,  which  takes  place  to  a  consi- 
lerable  extent  before  the  caecum  in  the  interior  begins  to  ramify.     Gra- 
dually, however,  the  cells  of  the  exterior  become  metamorphosed  into 
fibrous  tissue  for  the  investment  of  the  organ;  those  of  the  interior 
break  down  into  ducts  which  form  continuations  of  the  principal  canal ; 
whilst  those  which  occupy  the  intervening  space,  and  which  form  the 
^bulk  of  the  gland,  seem  to  be  developed  into  follicles,  and  to  give  origin 
^0  the  proper  secreting  cells.     As  this  is  going  on,  the  hepatic  mass  is 
-adually  removed  to  a  distance  from  the  wall  of  the  alimentary  canal ; 
i,nd  the  caecum  is  narrowed  and  lengthened,  so  as  to  become  a  mere  con- 
necting pedicle,  forming,  in  fact,  the  main  trunk  of  the  hepatic  duct. — 
"^he  development  of  the  Pancreas,  Salivary  glands,  &c.,  seems  to  follow 
the  same  plan. 

T19.  It  has  been  pointed  out  by  Prof.  Goodsir,  that  the  continued 
development  and  decay  of  the  glandular  structure, — in  other  words,  the 
elaboration  of  its  secretion, — may  take  place  in  two  difierent  modes.  In 
one  class  of  Glands,  the  parent-cell,  having  begun  to  develope  new  cells 
in  its  interior,  gives  way  at  one  point,  and  bursts  into  the  excretory 
duct,  so  as  to  become  an  open  follicle,  instead  of  a  closed  cell :  its  con- 
tained or  secondary  cells,  in  the  progress  of  their  own  growth,  draw 
into  themselves  the  matter  to  be  eliminated  from'^the  blood,  and,  having 
attained  their  full  term  of  life,  burst  or  liquefy,  so  as  to  discharge  their 
contents  into  the  cavity  of  the  follicle,  whence  they  pass  by  its  open 
orifice  into  the  excretory  duct :  and  a  continual  new  production  of  secon- 
dary cells  takes  place  from  the  germinal  spot,  or  nucleus,  at  the  extre- 
mity of  the  follicle,  which  is  here  a  permanent  structure.  In  this  form 
of  gland,  we  may  frequently  observe  the  secreting  cells  existing  in  vari- 
ous stages  of  development  within  a  single  follicle ;  their  size  increasing, 
and  the  character  of  their  contents  becoming  more  distinct  in  propor- 
tion to  their  distance  from  the  germinal  spot  (which  is  at  the  blind 
termination  of  the  follicle),  and  their  consequent  proximity  to  the  outlet 
(Fig.  114).  In  some  varieties  of  such  glands,  however,  as  in  the 
greatly-prolonged  follicles  or  tubuU  uriniferi  of  the  kidney,  the  produc- 


400  OF  SECRETION. 

tion  of  new  cells  does  not  take  place  from  a  single  germinal  spot  at  the 
extremity  of  the  follicle,  but  from  a  number  of  points  scattered  through 
its  entire  length. — In  the  second  type  of  Glandular  structures,  the 
parent-cell  does  not  remain  as  at  permanent  follicle ;  but,  having  come 
to  maturity  and  formed  a  connexion  with  the  excretory  duct,  it  dis- 
charges its  entire  contents  into  the  latter,  and  then  shrivels  up  and 
disappears,  to  be  replaced  by  newly-developed  follicles.  In  each  parent- 
cell  of  a  gland  formed  upon  this  type,  we  shall  find  all  its  secondary  or 
secreting  cells  at  nearly  the  same  grade  of  development ;  but  the  differ- 
ent parent-cells,  of  which  the  parenchyma  of  the  gland  is  composed,  are 
in  very  different  stages  of  growth  at  any  one  period  :  some  having  dis- 
charged their  contents  and  being  in  progress  of  disappearance,  whilst 
others  are  just  arriving  at  maturity  and  connecting  themselves  with  the 
excretory  duct ;  others  exhibiting  an  earlier  degree  of  development  of 
the  secondary  cells ;  others  presenting  the  latter  in  their  incipient  con- 
dition ;  whilst  others  are  themselves  just  starting  into  existence,  and  as 
yet  exhibit  no  traces  of  a  second  generation. — The  former  seems  to  be 
the  usual  type  of  the  ordinary  glands ;  the  latter  is  chiefly,  if  not  en- 
tirely, to  be  met  with  in  the  Spermatic  glands. 

2.    Of  the  Liver  and  the  Bile. 

720.  The  Liver  is  more  rarely  absent  than  any  other  Gland ;  being 
discoverable,  under  some  form  or  other,  in  all  but  the  very  lowest  mem- 
bers of  the  Animal  kingdom.  Its  simple  condition  in  the  higher  Po- 
lypes has  been  already  noticed  (§  716) ;  and  it  is  met  with,  under  an 
almost  equally  simple  form,  in  the  Starfish.  As  we  ascend  the  scale, 
however,  we  find  it  assuming  a  much  greater  importance,  and  presenting 
a  great  increase  in  size.  This  is  particularly  the  case  in  the  Mollus- 
cous classes ;  and  also  in  the  Crustacea,  a  class  which,  in  mode  of  respi- 
ration and  in  general  habits,  bears  a  great  resemblance  to  the  Mollusca. 
In  nearly  all  such  animals,  the  Liver  makes  up  a  large  proportion  of 
tl^e  mass  of  the  body.     It  usually  consists  of  a  series  of  large  follicles, 

Fig.  116.  Fig.  117. 


Lobule  of  Liyer  of  Squilla  Mantis ;  exterior.        Lobule  of  Liver  of  Squilla  Mantis,  cut  open. 

which  branch  out  into  smaller  ones  (Figs.  116  and  117),  and  of  which 
several  open  into  one  excretory  duct ;  but  these  ducts  remain  separate, 
and  discharge  their  contents  into  the  intestine  by  several  distinct  ori- 


I 


ft- 

COMPARATIVE   STRUCTURE   OF  THE  LIVER.  401 


re 

I 


fices. — In  Insects  and  other  air-breathing  Articulata,  however,  the 
iver  is  much  less  developed;  and  its  type  remains  much  simpler. 

e  usually  find  it  consisting  of  a  small  number  of  csecal  tubuli,  which 
open  separately  into  the  intestinal  canal,  just  below  the  stomach.  These 
tubuli  are  often  so  long,  as  to  pass  several  times  from  one  extremity  of 
the  visceral  cavity  to  the  other,  being  doubled  upon  themselves ;  in 
other  instances,  we  find  that  the  principal  tube  or  canal  is  beset  with 
rows  of  short  follicles,  somewhat  in  the  manner  of  Fig.  111.  But  they 
never  cluster  together  so  as  to  form  a  solid  glandular  mass.  The  low 
development  of  the  liver,  in  these  animals,  bears  an  evident  relation 
with  the  high  development  of  their  respiratory  apparatus ;  whilst,  the 
respiration  being  comparatively  feeble  in  the  aquatic  Mollusca  and 
"  rustacea,  the  development  of  the  liver  in  those  classes  is  enormous. 

7*21.  There  is  much  difiiculty  in  ascertaining  the  mode  in  which  the 
lementary  constituents  of  the  Liver  are  arranged,  in  the  fully-developed 
condition  of  that  organ  in  the  higher  Vertebrata.  At  an  early  period  of 
its  development,  as  already  remarked,  it  may  be  easily  shown  to  con- 
sist, in  the  Fowl,  of  a  series  of  distinct  caeca,  clustered  round  a  projec- 
tion from  the  intestinal  canal,  and  opening  separately  into  it  (Fig.  108) ; 
and  it  is  a  peculiarly  interesting  fact,  that  this  very  condition  should 
exist  as  the  permanent  form  of  the  Liver,  in  that  curious  little  fish,  the 
Amphioxus  or  Lancelot,  which  retains  the  embryonic  type  in  so  many 
parts  of  its  conformation.  In  the  Tadpole,  again,  the  distinct  caeca  are 
very  evident  (Fig.  118) ;  but  here  we  see  that  the  projection  of  the 
intestinal  canal,  instead  of  being  a  simple  wide  caecum,  has  become 
extended  in  length  and  contracted  in  diameter,  at  the  same  time  di- 
viding and  subdividing,  so  as  to  form  an  arborescent  excretory  duct, 
whose  ramifications  extend  through  the  entire  glandular  mass.  In  this 
manner,  then,  is  formed  the  complex  system  of  hepatic  ducts,  which  we 
find  in  the  liver  of  the  higher  Vertebrata,  branching  out  from  the  main 
trunk.  But  the  mode  in  which  the  ultimate  ramifications  of  these  are 
arranged,  and  their  relations  with  the  secreting  cells  which  make  up  the 
parenchyma  of  the  gland,  have  not  yet  been  fully  elucidated.  The  fol- 
lowing are  the  principal  facts,  that  have  been  ascertained  on  the  sub- 
ject. 

722.  The  entire  Liver  is  made  up  of  a  vast  number  of  minute  lobules^ 
of  irregular  form,  but  about  the  average  size  of  a  millet-seed.  Each  of 
these  lobules  contains  the  component  elements^  of  which  the  entire 
organ  is  made  up ;  namely,  branches  of  the  hepatic  artery  and  vein, 
branches  of  the  portal  vein,  branches  of  the  hepatic  ducts,  and  secreting 
cells.  The  lobules  are  connected  together  in  part  by  areolar  tissue,  but 
in  great  part  by  the  anastomosis  of  the  blood-vessels  and  hepatic  ducts, 
which  supply  the  adjoining  lobules ;  indeed  there  is  frequently  no 
definite  division  of  the  glandular  substance  into  lobules,  other  than  that 
which  is  marked  out  by  the  arrangement  of  these  canals  (Figs.  119  and 
121).  The  branches  of  the  Hepatic  Artery  are  principally  distributed 
upon  the  walls  of  the  hepatic  ducts,  and  upon  the  trunks  and  branches 
of  the  portal  and  hepatic  veins,  supplying  them  with  their  vasa  vasorum; 
also  upon  Glisson's  capsule  and  its  prolongations  into  the  substance  of 
the  liver,  which  prolongations  form  the  greatest  part  of  the  connecting 

26 


402 


OF  SECRETION. 


structure  that  holds  together  the  several  elements.     There  is  strong 
reason  to  believe,  that  the  blood  which  the  liver  receives  from  the 

Fig.  118. 


Lirer  of  TjUJpole;  showing  distinct  and  free  csecal  terminations  of  the  biliary  ducts. 

hepatic  artery  is  not  destined  to  supply  the  materials  for  the  biliary 
secretion,  until  it  has  become  venous  by  travelling  through  the  network, 
in  which  it  is  subservient  to  the  nutrition  of  the  tissues  it  permeates,  as 
it  is  in  other  parts  of  the  systemic  capillary  system. — The  supply  of 
blood,  from  which  the  materials  of  the  biliary  secretion  are  chiefly 
drawn,  is  afforded  by  the  Vena  Portce,  which  collects  it  as  a  Vein  from 
the  chylopoietic  viscera,  and  which  then  subdivides  as  an  Artery  to  dis- 
tribute it  to  the  different  parts  of  the  Liver.     Its  branches  proceed  to 

Fig.  119. 


Horizontal  section  of  three  superficial  lobules  of  the  Liver,  showing  the  two  principal  systems  of  blood- 
Tessels;  1, 1,  infra-lobular  veins,  proceeding  from  the  Hepatic  veins;  2,  2,  iwier-lobular  plexus,  formed  by 
branches  of  the  Portal  veins. 

the  capsules  of  the  lobules,  covering  the  whole  external  surface  of  the 
latter  with  their  ramifications,  and  sending  capillary  twigs  inwards, 
which  converge  towards  the  centre  of  each  lobule  (Fig.  119,  2,  2).     As 


STRUCTURE   OF  THE   LIVER. 


403 


le  principal  brandies  of  these  veins  ramify  in  the  spaces  between  the 

)bules,  they  are  termed  m^er-lobular  veins. — On  the  other  hand,  the 

tranches  of  the  Hepatic  Vein  pass  from  the  trunk  to  the  centre  of  each 

►bule,  from  which  they  send  out  diverging  capillary  twigs  (1,  1,)  ta- 

rards  the  circumference ;  and  these  last,  coming  into  connexion  with 

jhe  converging  capillaries  of  the  portal  vein,  establish  a  free  capillary 

communication  between  the  interior  and  exterior  of  each  lobule.     Thus 

fche  portal  blood  is  first  distributed  to  its  exterior,  then  penetrates  its 

mbstance,  and  then,  after  permeating  the  parenchymatous  substance 

numerous  minutely-divided  streams,  is  collected  and  carried  off  by 

the  hepatic  vein,  of  which  a  twig  originates  in  the  centre  of  each  lobule. 

">wing  to  the  peculiar  position  of  the  branches  of  the  hepatic  vein  in 

khe  centre  of  each  lobule,  the  lobules  are  appended  to  its  main  trunks 

ilmost  in  the  manner  of  leaves  upon  a  stem  (Fig.  120).     The  precise 

relation  of  the  capillaries  of  the  hepatic  artery  with  those  of  the  portal 

Fig.  120. 


Connexion  of  the  lobules  of  the  Liver  with  the  Hepatic  vein: — 1,  trunk  of  the  vein;  2,  2,  lobules  depend- 
ing from  its  branches,  like  leaves  on  a  tree ;  the  centre  of  each  being  occupied  by  a  venous  twig, — the  Intra- 
lobular Vein. 

and  venous  systems  has  not  yet  been  well  ascertained ;  but  there  seems 
reason  to  believe,  with  Mr.  Kiernan,  that  the  arterial  capillaries  dis- 
charge themselves  into  the  ultimate  ramifications  of  the  portal  vein ; 
and  that  thus  the  blood  of  the  former,  having  become  venous  by  trans- 
mission through  the  nutritive  capillaries  of  the  liver,  mingles  with  the 
other  venous  blood  collected  by  the  venae  portse,  to  supply  the  mate- 
rials of  the  secretory  function,  which  are  eliminated  from  it  during  its 
passage  into  the  hepatic  vein. 

723.  The  Hepatic  Ducts  also  seem  to  form  a  plexus  which  surrounds 
the  lobules,  connecting  them  together,  and  sending  branches  towards 
the  interior  of  each.  The  mode  in  which  they  terminate,  however,  and 
the  precise  relation  in  which  they  stand  to  the  hepatic  cells,  which  form 
nearly  the  entire  parenchyma  of  the  Gland,  has  not  yet  been  com- 
pletely elucidated.  There  seems  reason  to  believe,  however,  that  the 
tubular  plexus  extends  throughout  the  substance  of  the  lobule,  filling 
up  the  entire  space  not  occupied  by  the  blood-vessels  (its  membranous 
wall,  however,  being  with  difficulty  traceable,  owing  to  its  extreme 
tenuity) ;  and  that  the  hepatic  cells  are  contained  within  it,  as  within 
the  follicles  or  tubes  of  ordinary  glands.  These  cells  (which  are  easily 
obtained  in  a  separate  condition  by  scraping  a  piece  of  fresh  Liver) 
are  of  a  flattened  spheroidal  or  polygonal  form ;  and  their  diameter  is 
usually  from  l-800th  to  1-1 600th  of  an  inch.     Each  cell  presents  a  dis- 


404  OF  SECRETION. 

tinct  nucleus ;  and  it  is  usually  around  this,  that  the  yellowish  hue  of 
the  cell  is  the  deepest.  The  cavity  of  the  cell  is  chiefly  occupied  by 
biliary  matter,  much  of  which  is  in  the  condition  of  fine  granular  parti- 
cles too  minute  to  be  measured.     In  the  midst  of  these,  there  are  usually 

Fig.  121. 


Horizontal  section  of  two  superficial  lobules,  showing  the  interlobular  plexus  of  biliary  ducts :— 1,  1,  in- 
tralobular veins;  2,  2,  trunks  of  biliary  ducts,  proceeding  from  the  plexus  which  traverses  the  lobules;  3, 
interlobular  tissue;  4,  parenchyma  of  the  lobules. 

one  or  two  large  adipose  globules,  or  five  or  six  small  ones  (Fig.  122) ; 
but  the  amount  of  this  fatty  matter  is  liable  to  great  variation  (§  754). 

The  biliary  matter  which  these  cells  contain, 

Fig.  122.       ^  marks  them  out  as  the  real  agents  in  the  se- 

^^^^^  creting  process ;  this  process  consisting,  it  is 

^KBt^^m.  evident,  in  the  growth  of  the  hepatic  cells, 

^^^^|Hl.s  which,  in  the  course  of  their  development, 

^^^wBbLc  eliminate  from  the  blood  the  biliary  matter, 

'^  for  which  they  have  a  special  affinity.     The 

^VntTeoiul?'Sip'orp^?£^^    mode  in  which  the  particles  thus  eliminated, 

are  discharged  into  the  hepatic  ducts,  to  be 
by  them  conveyed  to  the  intestine,  cannot  be  understood,  until  the  rela- 
tion between  the  secreting  cells  and  the  ultimate  ramifications  of  the 
ducts  shall  have  been  more  precisely  determined. 

724.  The  Bile  which  has  been  secreted  by  the  hepatic  cells,  and 
which  has  found  its  way  into  the  ramifications  of  the  hepatic  ducts, 
may  be  directly  conveyed  by  the  trunk  of  the  latter  into  the  intestine, 
or  it  may  regurgitate  along  the  cystic  duct  into  the  gall-bladder.  It  is 
probable  that  the  secreting  process  is  constantly  going  on ;  although, 
as  in  other  cases,  it  may  vary  in  its  degree  of  activity  at  difierent 
times.  When  the  process  of  digestion  is  taking  place,  and  the  small 
intestine  is  filled  with  chyme,  there  is  probably  an  uninterrupted  flow 
of  bile  into  its  cavity ;  but  when  the  intestine  is  empty,  the  bile  seems 
not  to  be  admitted  into  it,  but  rather  to  flow  back  into  the  gall-bladder, 
in  which  it  is  stored  up,  as  in  a  reservoir,  until  the  time  when  it  may 
be  needed.  In  this  reservoir  it  undergoes  a  certain  degree  of  concen- 
tration, by  the  absorption  of  its  watery  part ;  and  it  also  becomes 
mixed  with  a  large  proportion  of  mucus,  which  is  secreted  by  the  walls 
of  the  gall-bladder. — As  the  analyses  of  Bile  have  been  chiefly  made 
upon  the  fluid  obtained  from  this  receptacle,  they  probably  over-esti- 
mate the  proportion  of  solid  matter  contained  in  this  secretion ;  which 


I  COMPOSITION   OF  JHE   BILE.  405 

is  usually  stated  at  from  8  to  9J  per  cent.  Of  this  solid  matter,  about  a 
tenth  consists  of  alkaline  and  earthy  salts,  corresponding  with  those  of 
the  blood;  whilst  the  remainder  is  made  up  of  organic  constituents. 
These  are  very  readily  decomposed,  and  enter  into  new  combinations 
with  the  substances  employed  to  separate  them ;  so  that  different 
Chemists,  by  employing  different  means  of  analysis,  have  obtained  re- 
sults which  seem  far  from  conformable.  All  are  agreed,  however,  that 
the  chief  part  of  the  solid  ingredients  of  bile  are  allied  to  fat  in  compo- 
sition ;  consisting  of  a  very  large  proportion  of  carbon  and  hydrogen, 
and  of  a  comparatively  small  amount  of  oxygen  and  azote.     According 

■  to  Prof.  Liebig,  the  organic  portion  of  ox-bile  may  be  represented  by 
the  formula  76  Carbon,  QQ  Hydrogen,  22  Oxygen,  and  2  Nitrogen, 

i  with  a  considerable  proportion  of  Sulphur.  This  substance,  essentially 
corresponding  with  the  bilic  acid,  choleic  acid,  bilin,  picromel,  &c.  of 
different  Chemists,  seems  to  be  a  fatty  acid  (§  261),  united  with  soda,  so 
as  to  constitute  a  soap.  In  healthy  bile,  the  proportion  of  Cholesterine 
appears  to  be  very  small,  and  it  is  held  in  solution  by  the  preceding 
ingredient ;  but  in  many  disordered  states,  and  especially  in  disease  of 
the  Gail-Bladder,  this  element  is  present  in  much  larger  amount ;  and 
it  usually  forms  the  principal,  if  not  the  sole  ingredient  in  biliary  con- 
cretions. It  is  a  white  crystallizable  fatty  matter,  somewhat  resem- 
bling spermaceti,  free  from  taste  and  odour,  and  composed  almost 
entirely  of  carbon  and  hydrogen ;  its  formula  is  36  Carbon,  32  Hydro- 
gen, and  1  Oxygen. — The  Colouring  matter  of  Bile  is  a  substance 
distinct  from  the  preceding ;  that  of  the  Ox  and  other  graminivorous 
animals  appears  to  be  identical,  or  nearly  so,  with  the  chlorophyll  of 
the  leaves  on  which  they  feed ;  but  that  of  Human  bile  seems  to  possess 

j_     different  properties,  and  to  be  derived  from  the  proper  constituents  of 

■    the  blood. 

725.  Regarding  the  destination  and  purposes  of  this  secretion  in  the 
Animal  economy,  the  following  may  be  considered  as  a  tolerably  com- 

»plete  summary ;  though  it  is  impossible  to  speak  with  precision  on  some 
points,  since  the  organic  constituents  of  the  Bile  are  liable  to  be  so 
easily  altered  by  various  reagents,  that  they  are  with  difficulty  recog- 
nised.— A  portion  of  the  Bile  unquestionably  passes  off,  in  Man  and 
most  other  animals,  with  the  faeces  ;  this  portion,  which  includes  the 
colouring  matter,  is  probably  that  which  would  be  most  injurious,  if 
retained  in  the  blood,  and  is  most  purely  excre^ientitious.  In ,  bilious 
'  diarrhoea,  and  under  the  influence  of  purgatives,  especially  mercurials, 
a  large  quantity  of  bile  is  discharged  per  anum,  apparently  almost 
unchanged.  But  in  the  healthy  state,  a  portion,  at  least,  of  the  soapy 
compound  seems  destined  for  reabsorption.  Just  as  ox-gall  is  com- 
monly used  to  remove  grease-spots,  by  its  solvent  power  for  fatty  mat- 
ter, so  does  the  bile  seem  to  act  in  the  living  body,  by  rendering  soluble 
the  fatty  matters  of  the  food,  and  thus  enabling  them  to  be  absorbed 
by  the  lacteals  (§  479).  The  fatty  matter  of  the  bile,  when  reabsorbed 
with  that  of  the  newly-ingested  food,  is  probably,  like  it,  carried  off  by 
the  respiratory  process  :  but  it  is  easily  shown,  that  the  biliary  matter 
cannot  supply  more  than  one-sixth  or  one-eighth  of  the  amount  of 
carbon  eliminated  from  the  lungs  in  the  form  of  carbonic  acid ;  and 


406  OF  ^ECKETION. 

that  it  cannot  be  (as  supposed  by  Liebig)  the  chief  fuel  of  the  process 
of  combustion,  which  is  kept  up  through  the  agency  of  those  organs. — 
The  secreting  action  of  the  Liver,  by  which  a  certain  product  is  entirely 
separated  from  the  blood,  constitutes,  however,  only  a  part  of  the  action 
of  that  organ ;  since,  as  already  shown  (§  493),  the  changes  which  it 
effects  in  the  alimentary  materials  newly  introduced  into  the  current 
of  the  circulation,  are  at  least  equally  important.  A  large  part  of  the 
bulk  of  the  Liver,  in  many  of  the  lower-  animals,  is  made  up  of  oleagi- 
nous matter;  which  appears  to  accumulate  in  the  hepatic  cells,  giving 
them  almost  the  character  of  fat-cells,  in  proportion  as  the  respiratory 
function  is  inactive.  Thus,  the  liver  is  very  large  and  fatty  in  Mollusca 
and  Crustacea;  whilst,  on  the  other  hand,  in  Insects  it  is  comparatively 
undeveloped.  In  Fishes,  again,  it  is  rich  in  oily  matter,  but  in  Mam- 
malia it  is  much  less  fatty  in  the  state  of  health ;  whilst  in  the  liver  of 
Birds,  scarcely  any  traces  of  fat  are  to  be  found. 

726.  The  elements  of  the  bile  may  be  altogether  supplied  by  the 
disintegration  of  the  tissues ;  and  this  must  certainly  be  the  case,  when 
the  amount  of  food  taken  is  no  more  than  enough  to  supply  the  waste 
of  the  system.  We  may  regard  it,  then,  as  one  office  of  the  Liver,  to 
remove  from  the  blood  such  products  of  that  disintegration,  as  are  rich 
in  carbon  and  hydrogen.  It  may  be  pretty  certainly  affirmed,  however, 
that  biliary  matter  does  not  pre-exist  as  such  in  the  blood ;  but  that  its 
elements  must  be  originally  present  there,  under  some  more  pernicious 
form.  For  it  is  found  that  the  total  suspension  of  the  secreting  action 
of  the  Liver,  whereby  the  excrementitious  matter  is  left  to  accumulate 
in  the  blood,  has  a  much  more  prejudicial  effect  upon  the  system,  than 
the  reabsorption  of  Bile  after  it  has  been  secreted,  in  consequence  of 
an  obstruction  to  its  discharge  through  the  ductus  choledochus ;  so  that 
it  may  be  inferred  that  the  noxious  products  of  the  disintegration  of 
the  tissues  are  transformed  into  the  comparatively  innocent  components 
of  Bile,  in  the  very  act  of  secretion. — But  there  can  be  little  doubt, 
that  the  Liver  has  also  for  its  office,  to  draw  off  from  the  blood  any 
superfluity  which  may  exist  in  the  non-azotized  compounds  derived  from 
the  food,  beyond  the  amount  that  is  requisite  for  the  supply  of  the 
respiratory  process,  or  that  can  be  deposited  as  fat.  For  we  conti- 
nually witness  the  results  of  habitual  excess  in  the  amount  of  such  sub- 
stances, in  producing  that  state  of  the  system  commonly  termed  bilious  ; 
of  which  all  the  symptoms  are  referable  to  the  accumulation  of  the  ele- 
ments of  the  bile  in  the  blood,  and  the  consequent  deterioration  in  the 
purity  of  the  circulating  fluid.  Where  a  tendency  to  such  a  state 
exists,  proper  means  should  be  taken  to  stimulate  the  liver  to  increased 
activity ;  but  the  chief  reliance  should  be  placed  on  the  avoidance  of 
those  articles  of  diet,  which  contain  a  large  proportion  of  non-azotized 
matter,  and  on  abstinence  from  superfluous  nutriment  of  any  de- 
scription. ■ 

3.    Of  the  Kidneys  and  the  Urine. 

727.  The  Kidneys  are  perhaps  the  most  purely  excreting  organs  in 
the  body ;  their  function  being  to  separate  from  the  blood  certain  matters 


STRUCTURE   OF  THE  KIDNEY. 


407 


lat  would  be  injurious  to  it  if  retained,  and  these  matters  being  des- 
led  to  immediate  and  complete  removal  from  the  system.     We  have 
leen  that,  in  the  Lungs,  the  excretion  of  Carbonic  acid  is  made  subser- 
ient  to  the  absorption  of  Oxygen ;  and  the  separation  of  a  fatty  acid 
•om  the  blood,  which  is  effected  by  the  Liver,  is  a  means  of  introducing 
new  supply  of  fatty  matter  into  the  system.     There  is  no  ulterior 
mrpose  of  this  kind  in  the  secreting  action  of  the  Kidney ;  the  product 
>f  which  is  invariably  conveyed  directly  to  an  outlet,  by  which  it  may  be 
ischarged  from  the  body.     Some  traces  of  Urinary  organs  may  be  de- 
leted in  most  of  the  higher  Invertebrata ;  but  it  is  in  Fishes,  that  they 
irst  present  a  considerable  development ;  and  in  ascending  through  the 
"ertebrated  series,  we  find  them  rapidly  increasing  in  the  complexity 
>f  their  organization,  and  in  their  functional  importance,  although  their 
ize  and  extent  are  not  so  great.     In  Fishes,  the  Kidneys  very  com- 
lonly  extend  the  whole  length  of  the  abdomen ;  and  they  consist  of 
fcufts  of  uniform-sized  tubules,  which  shoot  out  transversely  at  intervals 
rom  the  long  ureter,  and  which  are  connected  together  by  a  loose  web 

Fig.  123. 


Fig.  124. 


Kidney  of  foetal  Boa;  the  urinary  tubes  as  yet  short 
and  straight. 


Embryo  of  Green  Lizard: — a,  heart; 
b,  duplex  aorta;  c,  vena  cava;  d,  intes- 
tine; e,  liver;/,  rudiment  of  Wolffian 
body ;  g,  g,  rudiments  of  extremities. 

of  areolar  tissue,  that  supports  the  network  of  vessels  distributed  upon 
their  walls.  This  condition  of  the  Urinary  organs  is  very  analogous  to 
that  of  the  Corpus  Wolffianum  or  temporary  kidney  of  the  embryo  of 
higher  animals  (Fig.  123,  /).  A  similar  condition  is  found  in  the  true 
Kidney  of  higher  animals  at  an  early  grade  of  development  (as  shown 
in  Fig.  124) ;  the  tubuli  uriniferi  being  short  and  straight.  In  their 
more  advanced  condition,  however,  they  become  long  and  convoluted ; 
and  the  ramifications  of  the  capillary  vessels  come  into  very  close  rela- 
tion with  them  (Fig.  125).  It  is  in  the  higher  Reptiles,  that  we  first 
meet  with  the  distinction  between  the  cortical  and  medullary  substance ; 
the  former  being  the  part  in  which  the  blood-vessels  are  most  copiously 
distributed,  and  in  which  the  tubuli  have  the  most  convoluted  arrange- 
ment ;  and  the  latter  consisting  chiefly  of  straight  tubuli,  converging 
towards  the  points  at  which  they  discharge  themselves  into  the  ureter 
(Fig.  126).  The  bundles  of  tubuli  and  their  vascular  plexuses  remain 
distinct,  however,  in  Birds  and  in  the  lower  Mammalia,  so  as  to  give  to 


408 


OF   SECRETION. 


the  whole  gland  a'lobulated  character ;  but  in  the  Human  Kidney  they 
come  into   closer  contact :   and  the  vascular  connexion  between  the 


Fig.  126. 


Fig.  125. 


Portion  of  Kidney  from  Coluber:— a,  a,  vascular  trunk 
b,  6,  ureter ;  c,  c,  converging  fasciculi  of  tubuli  uriniferi. 


Pyramidal  fasciculi  of  tubuli  uri- 
niferi of  Bird,  terminating  in  one 
of  the  branches  of  the  ureter. 


plexuses  of  the  different  bundles  is  such,  as  to  prevent  any  separation 
into  distinct  lobules. 

728.  The  act  of  secretion  appears  to  be  effected,  as  in  other  Glands, 
by  the  epithelial  cells  lining  the  tubuli  uriniferi ;  these  cells  drawing  the 
materials  of  their  development  from  the  vascular  plexus  upon  the 
exterior  of  these  tubuli ;  and  delivering  them  up,  when  they  have  com- 
pleted their  own  term  of  existence,  to  be  carried  off  through  the  open 


Fig.  127. 


Fig.  128. 


A  section  of  the  Kidney,  surmounted  by  the  supra-re- 
nal capsule ;  the  swellings  upon  the  surface  mark  the 
original  constitution  of  the  organ,  as  made  up  of  dis- 
tinct lobes. — 1.  The  supra-renal  capsule.  2.  The  vas- 
cular portion  of  the  kidney.  3, 3.  Its  tubular  portion, 
consisting  of  cones.  4,  4.  Two  of  the  papillfe  project- 
ing into  their  corresponding  calices.  5,  5.  5.  The 
three  infundibula;  the  middle  5  is  situated  in  the 
mouth  of  a  calyx.    6.  The  pelvis.    7.  The  ureter. 


Portion  of  the  Kidney  of  a  new- 
born infant: — a,  natural  size;  1,  1, 
Corpora  Malpighiana,  as  dispersed 
points  in  the  cortical  substance;  2, 
papilla;  b,  a  smaller  part  magnified; 
1,  1,  Corpora  Malpighiana;  2,  2,  tu- 
buli uriniferi. 


orifices  of  the  tubuli.     But  the  Kidney  contains  another  apparatus,  of 
a  very  peculiar  description ;  which  appears  specially  destined  for  the 


I 


STRUCTURE  OF  THE  KIDNEY.  409 


separation  of  the  superfluous j^wzc?  of  the  system.  When  a  section  of  the 
Kidney  is  slightly  magnified  (Fig.  128,  b),  the  cut  surface  is  seen  to  be 
studded  by  a  number  of  little  dark  points  ;  each  one  of  which,  when  exa- 
mined under  a  higher  magnifying  power,  is  found  to  consist  of  a  knot  of 
minute  blood-vessels,  formed  by  the  convolutions  of  thin-walled  capilla- 
ries (Fig.  129,  m).  It  has  been  shown  by  Mr.  Bowman,  that  each  one 
of  these  knots  is  included  in  a  flask-like  capsular  dilatation,  connected 
with  one  of  the  tubuli  uriniferi ;  several  such  capsules,  it  appears,  being 
ually  developed  from  the  sides  of  each  tubulus,  like  currants  upon  a 
Ik.  Each  of  these  vascular  tufts  (called  Malpighian  bodies,  after 
heir  discoverer)  is  directly  supplied  by  a  branch  of  the  renal  artery 
(Fig.  129,  af) ;  which,  upon  piercing  the  capsule,  subdivides  into  a 
group  of  capillaries ;  and  these,  after  forming  the  convoluted  tuft,  coa- 
lesce into  a  single  efi'erent  trunk  (e/),  which  may  be  considered  as  re- 
presenting (in  a  small  way)  the  vena  portse.  For  the  efi'erent  trunks 
of  the  Malpighian  bodies  discharge  their  blood  into  the  capillary  plexus, 

Fig.  129. 


b 


Distribution  of  the  Renal  vessels,  from  Kidney  of  Horse:— a,  branch  of  Renal  artery;  af,  afferent  vessel : 
m,  m,  Malpighian  tufts;  ef,  ef,  efferent  vessels;  p,  vascular  plexus  surrounding  the  tubes;  st,  straight  tube; 
ct,  convoluted  tube.    Magnified  about  30  diameters. 

which  surrounds  the  tubuli  uriniferi,  and  from  which  the  solid  matter 
of  the  urinary  secretion  is  elaborated ;  just  as  the  vena  portse  supplies 
the  capillary  plexus,  from  which  the  biliary  secretion  is  elaborated  in 
the  liver.  In  Reptiles  (in  which,  as  in  Fishes,  the  kidney  is  partly 
supplied  by  the  hepatic  portal  system),  the  efi'erent  vessels  of  the  Mal- 
pighian bodies  unite  with  branches  of  the  portal  vein  to  form  the  secre- 
ting plexus  around  the  tubuli  uriniferi ;  and  even  in  Birds  this  arrange- 
ment still  seems  to  prevail  to  a  certain  extent.  Thus  all  the  blood 
which  the  secreting  plexus  receives,  has  already  passed,  in  each  case, 
through  a  set  of  capillaries  within  or  without  the  organ ;  those,  namely, 
of  the  Malpighian  bodies,  or  those  of  the  parts  supplying  the  hepatic 
portal  system. — The  special  purpose  of  the  Malpighian  bodies  appears 
to  be,  to  allow  of  the  transudation  of  the  water  of  the  blood,  which  is 
filtered  ofi'  (so  to  speak)  through  the  thin  walls  of  their  capillaries,  and 
thus  passes  into  the  tubuli  uriniferi.  It  is  well  known  that  the  fluid 
and  solid  constituents  of  the  urinary  secretion  bear  no  constant  relation 
to  each  other ;  the  amount  of  fluid  depending  mainly  upon  the  degree 


410  OF   SECRETION. 

of  fulness  of  the  blood-vessels ;  whilst  the  amount  of  solid  matter  is 
governed,  as  we  shall  presently  see,  by  the  previous  waste  of  the  tis- 
sues. The  quantity  of  fluid  in  the  blood-vessels  is  governed  by  the 
relative  amount  that  has  been  absorbed,  and  that  which  has  been 
exhaled  from  the  skin ;  so  that  the  quantity  to  be  drawn  off  by  the 
Kidneys  is  increased,  either  by  augmented  absorption,  or  by  diminished 
exhalation.  The  Malpighian  bodies  seem  to  act  the  part  of  a  system 
of  regulating  valves ;  permitting  the  transudation  of  only  enough  fluid 
to  dissolve  the  solid  matter,  when  there  is  no  superfluity  of  water  in 
the  vessels ;  but  allowing  the  escape  of  an  almost  unlimited  amount  of 
it,  when  increased  imbibition  has  rendered  the  vessels  unusually  turgid. 

729.  The  average  amount  of  Urine  excreted  in  twenty-four  hours, 
by  adults  who  do  not  drink  more  than  the  wants  of  nature  require,  is 
probably  from  30  to  40  oz. ;  and  its  average  specific  gravity  may  be 
about  1020.  The  quantity  of  fluid  is  usually  less,  and  the  specific 
gravity  of  the  secretion  consequently  greater,  in  summer  than  in  win- 
ter, on  account  of  the  larger  proportion  of  fluid  exhaled  by  the  skin 
during  the  former  season.  The  quantity  of  solid  matter  has  been  found 
to  vary,  within  the  limits  of  ordinary  health,  from  3-6  to  6*7  per  cent.; 
and  the  extent  of  variation  in  disease  is  doubtless  much  greater.  About 
one-third  of  the  solid  matter  is  made  up  of  alkaline  and  earthy  salts  ;  and 
the  remainder  is  made  up  of  organic  compounds.  The  salts  are  partly 
those  of  the  blood,  which  will  not  be  separated  during  the  transudation 
of  the  serum  through  the  membranous  walls  of  the  Malpighian  capilla- 
ries, although  the  albuminous  matter  is  kept  back  (§  196).  But  there 
is  a  much  larger  proportion  of  the  alkaline  and  earthy  phosphates  in 
the  urine,  than  is  present  in  the  blood ;  and  this  is  liable  to  a  further 
increase  under  circumstances  to  be  presently  alluded  to. — The  urine  is 
normally  acid,  but  the  degree  of  its  acidity  has  been  shown  by  Dr. 
Bence  Jones  to  be  continually  changing,  and  to  be  considerably  affected 
by  food ;  being  augmented  by  vegetable,  and  decreased  by  animal  food. 
What  the  acid  may  be  to  which  the  acidity  is  due,  is  yet  uncertain ; 
possibly  it  is  not  always  the  same. 

730.  The  organic  compounds  present  in  the  Urinary  secretion  (in  its 
healthy  state  at  least.)  are  undoubtedly  the  result  of  the  waste  or  disin- 
tegration of  the  animal  fabric ;  as  well  as  (in  certain  cases)  of  the  de- 
composition of  constituents  of  the  blood,  which  have  never  undergone 
conversion  into  organized  tissue.  Their  unfitness  to  be  retained*  within 
the  system,  is  proved  by  the  fatal  results  which  speedily  ensue  when 
their  elimination  by  the  secreting  process  receives  a  check ;  and  also 
by  the  crystalline  form,  in  which  the  most  characteristic  of  them  pre- 
sent themselves, — such  a  form  being  altogether  incompatible  with  the 
possession  of  plastic  or  organizable  properties.  Various  well-defined 
compounds  present  themselves  in  the  Urine  of  different  classes  of  ani- 
mals ;  and  they  are  nearly  all  peculiarly  rich  in  Nitrogen  and  deficient 
in  Carbon,  as  compared  with  the  Albuminous  compounds.  Thus,  whilst 
the  proportion  of  Nitrogen  in  Albumen  is  (by  weight)  as  1  :  6*24  of  the 
whole,  it  is  in  Urea  as  1  :  2*14,  in  Allantoin  as  1  :  2*21,  in  Kreatine 
as  1  :  2-69,  in  Uric  acid  as  1  :  3*00,  and  in  Kreatine  as  1  :  3*12.  The 
only  exception  is  in  the  case  of  Hippuric  acid,  which  is  discharged 


I 


COMPOSITION   OF  THE   URINE.  411 


largely  by  herbivorous  animals,  and  in  which  the  proportion  of  Nitro- 
gen is  as  1  :  12-14.  On  the  other  hand,  whilst  the  proportion  of  Car- 
bon in  Albumen  is  as  1  :  1*80,  it  is  in  Kreatinine  as  1  :  2*35,  in  Krea- 
tine  as  1  :  2*73,  in  Uric  Acid  as  1  :  9-80,  in  Allantoin  1  :  3*87,  and  in 
Urea  as  1  :  5-00.  Here,  again,  Hippuric  acid  is  exceptional ;  for  its 
Carbon  is  as  1  :  1*57  of  the  whole,  or  in  larger  proportion  than  in  Al- 
bumen.— We  may  say,  then,  that  the  characteristic  components  of  the 
Urinary  secretion  are  such  products  of  the  waste  of  the  azotized  tissues, 
as,  from  containing  nitrogen  in  large  proportion,  are  not  adapted  for 
elimination,  either  by  the  respiratory  process,  or  by  the  biliary  excre- 
tion. The  only  exception  is  in  the  case  of  Hippuric  acid";  and  the  large 
proportion  of  carbon  and  the  small  proportion  of  nitrogen  contained  in 
this  substance,  appear  due  to  the  great^  excess  of  non-azotized  com- 
•pounds  in  the  food  of  the  animals  voiding  it. 

731.  Of  the  compounds  just  enumerated,  the  most  important,  in 
Man,  is  that  which  is  named  Urea.  It  exists  in  Urine  in  a  state  of 
perfect  solution ;  and  may  be  readily  separated  from  it  in  the  form  of 
transparent  colourless  crystals,  which  have  a  faint  and  peculiar  but  not 
urinous  odour.  In  its  ultimate  composition  it  is  identical  with  Cyanate 
of  Ammonia,  being  made  up  of  2  Carbon,  4  Hydrogen,  2  Nitrogen,  and 
2  Oxygen, — a  formula  much  more  simple  than  that  of  almost  any  other 
organic  substance.  The  amount  of  Urea  in  the  Urine  is  liable  to  very 
great  variation,  in  accordance  with  the  degree  in  which  the  disintegrating 
process  has  been  taking  place  in  the  solid  fabric ;  and  also  in  confor- 
mity with  the  amount  of  azotized  matter,  which  has  been  taken  in  as 
food.  Supposing  that  the  latter  were  so  precisely  adjusted  to  the  wants 
of  the  system,  as  to  supply  only  that  which  is  required  for  its  mainte- 
nance, we  might  then  measure  the  amount  of  previous  waste,  by  the 
quantity  of  Urea  present  in  the  Urine.  There  can  be  no  doubt  as  to 
the  fact,  that,  other  things  being  equal,  the  amount  of  Urea  is  greatly 
increased  by  any  unusual  exertion  of  the  Muscular  system ;  but  such 
an  increase  cannot  be  invariably,  or  even  usually,  attributed  to  this 
cause ;  since  it  is  equally  certain,  that  any  superfluity  in  the  amount  of 
azotized  matter  received  into  the  blood,  must  be  drawn  off"  by  the  uri- 
nary excretion,  and  thus  that  an  increase  in  the  quantity  of  urea  may 
be  occasioned  by  an  excessive  use  of  proteine-compounds  as  articles  of 
food.  The  average  proportion  of  Urea,  under  ordinary  circumstances 
as  to  diet  and  exercise,  seems  to  be  from  20  to  3^5  parts  in  1000 ;  but 
it  may  be  raised  to  45  parts  by  violent  exercise,  and  to  53  parts  by  an 
exclusively  animal  diet ;  whilst  it  may  fall  as  low  as  from  12  to  15 
parts,  when  the  diet  is  deficient  in  azotized  matter.  The  total  daily 
excretion  of  Urea  in  adult  males  seems  to  average  about  430  grains, 
and  that  of  females  nearly  300  grains,  but  these  averages  may  be 
widely  departed  from,  on  the  side  either  of  excess  or  diminution, 
according  to  the  circumstances  already  noticed.  It  is  interesting  to 
observe,  that  children  of  eight  years  old  excrete,  on  the  average,  half 
as  much  Urea  as  adults ;  whilst,  in  very  old  persons,  the  quantity  sinks 
to  one-third,  or  even  less.  In  proportion  to  their  relative  bulks,  there- 
fore, children  excrete  at  least  two  or  three  times  the  quantity  of  urea 
that  is  set  free  by  adults,  and  four  or  five  times  that  which  is  excreted 


k 


412  OF   SECRETION. 

by  old  persons, — a  fact  which  corresponds  with  other  indications  of  the 
far  greater  rapidity  of  interstitial  change  in  the  earlier  periods  of  life, 
than  in  adult  or  advanced  age. 

732.  There  is  an  organic  compound,  nearly  allied  to  Uriea  in  compo- 
sition, but  differing  from  it  in  its  distinctly  acid  properties,  and  also  in 
its  comparative  insolubility.  This  substance,  termed  Uric  or  Lithic 
Acid,  forms  but  a  small  proportion  of  the  solid  matter  of  Human  Urine 
in  the  state  of  health ;  but  it  is  the  chief  element  in  the  Urine  of  the 
lower  Vertebrata ;  and  its  presence  in  too  large  a  proportion  is  a  fre- 
quent source  of  disease  in  Man.  Its  ultimate  composition  is  10  Car- 
bon, 4  Hydrogen,  4  Nitrogen,  6  Oxygen ;  it  crystallizes  in  fine  scales 
of  a  brilliant  white  colour  and  silky  lustre ;  and  it  is  so  sparingly  solu- 
ble in  water,  that  at  least  10,000  times  its  own  weight  of  fluid  is  re- 
quired to  dissolve  it.  In  healthy  Human  urine,  it  is  in  a  state  of  perfect- 
solution,  but  it  is  precipitated  by  the  addition  of  a  small  quantity  of  any 
acid,  even  the  Carbonic  :  it  is  evident,  therefore,  that  it  is  held  in  solu- 
tion by  union  with  some  base,  and  it  seems  probable  that  this  base  is 
ammonia.  According  to  Dr.  Bence  Jones,  the  first  precipitate  thrown 
down  by  the  addition  of  hydrochloric  acid  to  ordinary  urine,  is  urate  of 
ammonia,  which  is  less  soluble  in  acid  than  in  neutral  or  alkaline  urine ; 
and  it  is  only  after  prolonged  contact  with  the  hydrochloric  acid,  that 
this  salt  is  decomposed,  and  uric  acid  left  behind.  The  solubility  of 
urate  of  ammonia  is  much  greater  in  warm  than  in  cold  urine  ;  and  hence 
it  frequently  happens,  that  urine  which  is  clear  when  voided,  gives  a  pre- 
cipitate of  urate  of  ammonia  on  cooling. 

733.  The  proportion  of  Uric  acid  in  healthy  urine  seldom  rises  above 
1  part  in  1000,  and  the  quantity  excreted  daily  is  usually  from  6  to  10 
grains.  The  circumstances  under  which  it  varies,  however,  have  not 
been  clearly  determined.  The  absolute  quantity  in  the  urine  bears  no 
proportion  to  its  acidity,  nor  is  it  indicated  by  the  amount  of  deposit ; 
for  the  acidity  of  the  urine  depends  upon  the  presence  of  other  acids ; 
and  a  deposit  of  urate  of  ammonia  may  be  due  to  an  excess  of  acid, 
diminishing  its  solubility,  rather  than  to  an  excess  of  the  substance 
itself.  Thus  it  may  happen  that  a  precipitate  of  urate  of  ammonia 
may  be  formed,  when  it  is  not  present  in  any  undue  proportion,  in  con- 
sequence of  the  acid  state  of  the  urine ;  whilst,  on  the  other  hand,  there 
may  be  a  large  excess  of  urate  of  ammonia  in  the  urine  without  any 
precipitate,  if  the  urine  should  be  alkaline.  In  disordered  states  of  the 
system,  there  is  often  a  great  increase  in  the  amount  of  uric  acid  in  the 
urine ;  and  there  can  be  no  doubt  that  this  increase  is  partly  controlla- 
ble by  the  reduction  of  the  proportion  of  azotized  matter  in  the  food. 
In  some  of  these  cases,  free  uric  acid  is  deposited,  in  consequence  of 
the  decomposition  of  the  urate  of  ammonia  by  a  large  excess  of  acid  in 
the  urine.  In  attacks  of  gout,  urate  of  soda  is  separated  from  the  cir- 
culating blood,  and  is  deposited  in  the  tissues  around  the  affected  joints, 
forming  the  concretions  termed  "  chalk-stones  ;"  and  in  this  state  of  the 
system,  uric  acid  may  be  detected  in  the  blood. 

734.  There  seems  reason  to  believe  that  we  are  to  regard  Jlippurio 
acid  as  a  normal  element  of  the  Urine  of  Man  ;  although  it  has  been 
usually  supposed  to  be  restricted  to  the  Herbivorous  quadrupeds,  where 


COMPOSITION   OF   THE   URINE.  413 

it  replaces  Uric  Acid.  Its  composition  and  properties  are  very  diffe- 
rent from  those  of  that  substance.  When  pure,  it  forms  long,  transpa- 
rent, four-sided  prisms ;  it  is  soluble  in  400  parts  of  cold  water,  and 
dissolves  readily  at  a  boiling  heat ;  and  it  has  a  strong  acid  reaction^ 
with  a  bitterish  taste.  It  is  composed  of  18  Carbon,  8  Hydrogen,  1 
Nitrogen,  and  5  Oxygen,  with  1  equiv.  of  Water.  When  exposed  to  a 
high  temperature,  or  subjected  to  the  putrefactive  process,  it  is  partly 
converted  into  Benzoic  acid ;  and  it  is  on  the  presence  of  the  latter  in 
putrefied  Human  Urine,  that  the  belief  in  the  existence  of  Hippuric 
acid  in  the  same  fluid  when  fresh,  is  chiefly  grounded.  It  is  a  curious 
fact,  that  the  administration  of  Benzoic  acid  causes  the  appearance  of 
a  large  additional  quantity  of  Hippuric  acid  in  the  Urine,  so  that  its 
presence  is  then  sufficiently  evident ;  and  this  seems  to  be  due  to  the 
union  of  the  benzoic  acid  within  the  system,  either  with  glycocoll  (§  176), 
or  with  the  elements  which  would  have  formed  it ;  for  one  equivalent  of 
benzoic  acid,  added  to  one  of  glycocoll,  gives  the  precise  equivalent  of 
hippuric  acid.  It  does  not  appear  that,  as  once  asserted,  the  adminis- 
tration of  benzoic  acid  diminishes  the  quantity  of  uric  acid  normally 
present  in  the  urine ;  but  it  seems  to  bring  down  the  excess,  where  such 
exists,  to  about  the  normal  quantity ;  and  it  may  thus  be  employed  with 
advantage  in  cases  of  uric  acid  gravel. 

735.  Much  discussion  has  taken  place,  as  to  the  normal  presence  of 
Lactic  acid  in  the  urine  ;  and  the  question  cannot  even  now  be  regarded 
as  completely  determined.  It  is  certain  that  the  peculiar  crystalline 
compound,  procurable  by  treating  the  urine  with  zinc  in  solution,  is  not 
as  was  formerly  maintained,  a  lactate  of  zinc ;  but  that  its  composition 
is  altogether  difi"erent,  as  will  be  presently  explained.  But,  on  the 
other  hand,  it  appears  from  the  researches  of  Lehmann  and  others, 
that  lactic  acid  is  usually  present  in  small  quantity  in  healthy  urine ; 
and  that  its  quantity  may  be  increased  under  such  conditions,  as  either 
tend  to  augment  the  quantity  of  lactic  acid  in  the  blood,  or  to  obstruct 
its  elimination  by  the  respiratory  process.  Thus  an  excess  of  farina- 
ceous food,  which  furnishes  sugar  and  lactic  acid  faster  than  they  can 
be  thrown  off  as  carbonic  acid  and  water ;  or  an  excess  of  exertion  of 
the  muscles,  of  whose  disintegration  lactic  acid  appears  to  be  one  of 
the  results ;  or  pulmonary  diseases,  which  interfere  with  the  normal 
aeration  of  the  blood ;  all  favour  the  appearance  of  lactic  acid  in  the 
urine.  It  seems  to  be  constant  in  herbivorous  animals,  and  in  patients 
suffering  under  chronic  bronchitis,  pulmonary  emphysema,  and  similar 
disorders. — The  urine  of  Man,  more  uniformly  contains,  however,  two 
substances  termed  Kreatine  and  Kreatinine ;  which  seem  to  be  the 
result  of  the  degeneration  of  the  muscles,  as  they  may  be  obtained  from 
the  juice  of  raw  flesh.  The  former  of  these,  which  is  found  in  largest 
amount,  is  a  neutral  substance,  crystallizing  in  long  prisms,  sparingly 
soluble  in  cold  water,  but  dissolving  readily  in  warm.  By  the  action 
of  strong  acids,  kreatine  may  be  readily  converted  into  kreatinine, 
which  only  differs  from  it  in  composition  by  containing  two  proportion- 
als less  of  the  elements  of  water,  but  is  a  substance  of  very  different 
chemical  relations,  having  a  strong  alkaline  reaction,  and  serving  as  a 
powerful  organic  base  to  acids.     When  long  boiled  with^  caustic  baryta, 


414  ^  OF   SECRETION. 

kreatinine  is  gradually  resolved  into  urea;  and  thus  it  would  seem  as  if 
they  hold  an  intermediate  position  between  the  components  of  the  orga- 
nized tissues  and  the  urea  which  may  be  considered  as  the  ultimate  pro- 
duct of  their  metamorphosis  within  the  body.  The  peculiar  crystalline 
compound  just  referred  to,  as  having  been  formerly  supposed  to  be  lac- 
tate of  zinc,  has  been  shown  to  be  really  formed  by  a  combination  of 
zinc  with  a  compound  of  kreatine  and  kreatinine. 

736.  Of  the  substances  ranked  under  the  head  of  Extraetive  blatters, 
little  is  definitely  known ;  it  appears,  however,  from  recent  researches, 
that  they  are  peculiarly  rich  in  carbon,  and  that  they  are  liable  to  be 
greatly  augmented,  either  by  an  excess  of  non-azotized  matter  in  the 
food,  or  by  any  impediment  to  the  action  of  the  liver  or  lungs.  A 
yellow  extractive  has  been  separated  by  Scherer,  which  he  regards  as 
proceeding  from  the  final  metamorphosis  of  the  haematin  of  the  blood ; 
and  this  seems  nearly  related  to  the  purpurine,  which  sometimes  gives 
a  deep  colour  to  the  sediment  of  urate  of  ammonia,  and  which  is  pecu- 
liarly liable  to  appear  when  the  functional  activity  of  the  liver  is  below 
par.  The  ordinary  colouring-matter  of  bile  often  presents  itself  in  the 
urine  in  cases  of  jaundice :  and,  as  Dr.  Golding  Bird  has  pointed  out, 
there  is  a  close  similarity  in  composition  between  these  three  coloured 
compounds,  indicating  a  derivation  from  the  same  source.  A  sulphur 
extractive  has  also  been  obtained  from  the  urine :  in  which  (as  in  the 
bile)  there  is  a  considerable  proportion  of  free  sulphur. 

737.  The  Urine  also  contains  a  considerable  amount  of  Saline  matter, 
of  which  the  acids  as  well  as  the  bases  are  derived  from  the  mineral 
kingdom ;  and  the  excretion  of  them,  after  they  have  served  their  pur- 
pose in  the  economy,  appears  to  be  one  of  the  chief  functions  of  the 
Kidney.  Of  these  a  part  may  find  their  way  directly  into  the  urine 
from  the  serum  of  the  blood,  when  its  water  is  being  filtered  ofi"  (so  to 
speak)  through  the  walls  of  the  Malpighian  capillaries ;  for  although, 
from  the  peculiar  properties  of  animal  membranes  (§  196),  the  albumi- 
nous constituents  of  the  serum  are  held  back,  the  saline  matter,  which  is 
in  a  state  of  perfect  solution,  must  pass  with  the  water.  This  is  pro- 
bably the  chief  source  of  the  large  quantity  of  the  muriates  of  soda  and 
ammonia  contained  in  the  urine.  But  the  tJrinary  secretion  seems  to  be 
specially  destined  to  eliminate  the  saline  compounds,  which  are  formed 
by  the  acidification  of  the  Sulphur  and  Phosphorus,  taken  in  with  the 
proteine-compounds  as  food.  These  substances  are  united  with  Oxygen 
in  the  system,  and  are  thus  converted  into  Sulphuric  and  Phosphoric 
acids  ;  which  acids  unite  with  alkaline  bases,  that  were  ingested  in 
combination  with  Citric,  Tartaric,  Oxalic,  and  orther  organic  acids ; 
the  latter  undergoing  decomposition  within  the  system,  and  leaving 
the  bases  ready  to  unite  with  others.  Such  weakly-combined  bases 
abound  in  the  food  of  Herbivorous  animals ;  and  their  urine  is  almost 
invariably  alkaline^  the  quantity  of  the  Sulphuric  and  Phosphoric  acids 
generated  in  the  system  not  being  sufficient  to  neutralize  it.  On  the 
other  hand,  they  are  nearly  absent  in  the  food  of  the  Carnivora ;  and 
their  urine  is  therefore  almost  invariably  acid,  from  the  want  of  neutra- 
lization of  the  Sulphuric  and  Phosphoric  acids. 

738.  The  Alkaline  Sulphates,  whether  taken-in  as  such,  or  formed  in 


i 


COMPOSITION   OF  THE   URINE.  415 

e  manner  now  described,  are  soluble  enough  to  be  always  passed  off  in 
a  fluid  form ;  but  this  is  not  uniformly  the  case  with  the  Phosphates, 
hich  are  frequently  deposited  as  sediments  of  a  dead-white  aspect, 
metimes  crystalline,  and  sometimes  wholly  or  partly  amorphous.  The 
ystalline,  sediment  consists  of  the  triple  phosphate,  or  phosphate  of 
ammonia  and  magnesia ;  the  amorphous  contains  an  admixture  of  the 
phosphate  of  lime.  The  urine,  when  these  are  deposited,' is  usually 
alkaline,  sometimes  very  decidedly  so ;  and  there  is  reason  to  think  that, 
many  cases,  this  alkaline  character,  and  the  deposit  of  phosphatic 
diments,  are  due  to  an  alkaline  secretion  from  the  walls  of  the  bladder 
nd  urinary  passages,  which  results  from  an  irritable  state  of  their  mem- 
brane,— the  urine,  as  secreted  by  the  kidney,  having  its  usual  properties. 
That  an  alkaline  condition  of  the  urine,  resulting  from  the  presence  of 
an  unusual  amount  of  bases,  is  capable  of  producing  a  phosphatic  deposit, 
is  shown  by  the  simple  experiment  of  adding  ammonia  to  healthy  urine, 
which  will  occasion  a  precipitation  of  the  triple  phosphate. 

739.  But  there  can  be  little  doubt,  that  a  frequent  cause  of  the  de- 
posit is  excessive  production  of  phosphate  salts,  arising  from  the  in- 
creased waste  or  disintegration  of  Nervous  matter,  which  takes  place 
when  it  is  in  a  state  of  unusual  activity,  either  from  intense  thought, 
from  prolonged  exertion,  or  from  continued  anxiety.  The  general  prin- 
ciples already  set  forth,  in  regard  to  the  dependence  of  the  functional 
activity  of  the  Nervous  Centres  upon  a  supply  of  arterialized  blood 
(§  384),  show  the  probability  that  every  act  of  theirs  involves  the  oxy- 
genation of  a  certain  quantity  of  nervous  matter.  In  this  oxygenation, 
phosphoric  acid  wull  be  produced,  from  the  large  amount  of  phosphorus 
contained  in  the  nervous  matter ;  and  this  will  unite  in  part  with  am- 
monia, which  is  perhaps  set  free  by  the  same  metamorphosis,  or  is  de- 
rived from  other  sources ;  and  in  part  with  bases  derived  from  the  food. 
The  experience  of  every  studious  man  must  have  shown  him  (if  he  make 
any  observations  on  the  matter  at  all)  the  frequent  coincidence  between 
the  presence  of  phosphatic  deposits  in  his  urine,  and  an  excess  of  men- 
tal labour ;  and  there  are  many  instances  on  record,  in  which  the  peri- 
odical recurrence  of  the  latter  has  been  so  invariably  followed  by  the 
recurrence  of  the  former,  that  no  reasonable  doubt  can  exist  as  to  their 
mutual  connexion. 

740.  It  is  very  important  for  the  successful  treatment  of  those  Uri- 
nary deposits,  which  consist  of  the  normal  elem-fents  of  the  Urine, — 
namely,  Lithic  Acid,  and  the  Phosphates, — that  the  leading  facts  al- 
ready stated  should  be  borne  continually  in  mind.  In  the  first  place, 
these  sediments  may  depend  upon  the  general  condition  of  the  fluid, 
and  not  upon  any  excess  in  the  constituents  of  which  they  are  com- 
posed ;  thus  a  lithic  deposit  may  result  from  the  presence  of  an  excess 
of  some  other  acid  in  the  urine ;  and  a  phosphatic  sediment  may  be 
produced  by  the  excess  of  bases.  In  such  cases,  then,  our  treatment 
should  be  directed,  not  to  diminish  the  quantity  of  the  peculiar  consti- 
tuents of  the  deposits,  but  to  rectify  the  state  of  the  Urine  on  which 
their  precipitation  depends.  But,  in  the  second  place,  the  sediments 
may  be  present  in  such  great  amount,  as  to  indicate  that  their  consti- 
tuents are  present  in  the  urine  to  an  excessive  degree ;  and  our  treat- 


416  OP   SECRETION. 

ment  must  then  be  directed  towards  the  diminution  of  the  quantity  pro- 
duced. Thus  the  tendency  to  lithic  acid  deposit  may  be  frequently 
cured,  by  simply  diminishing  the  quantity  of  azotized  matter  in  the 
food ;  and  the  undue  formation  of  the  phosphates  may  be  often  kept  in 
check  by  that  mental  repose,  which  is  peculiarly  required  after  long- 
continued  and  severe  exercise  of  the  intellectual  faculties,  or  strong  ex- 
citement of  the  feelings. 

741.  There  is  no  doubt  whatever,  that  the  total  suspension  of  the 
Urinary  secretion  is  productive  of  rapidly-fatal  results,  from  the  accu- 
mulation of  the  elements  of  the  secretion  in  the  blood ;  and  it  would 
appear,  that  the  tissue  on  which  their  presence  in  the  circulating  fluid 
exerts  the  most  injurious  eifects,  is  the  Nervous.  It  is  probable  that 
Urea  is  the  substance  which  is  most  directly  concerned  in  producing 
the  noxious  influence ;  and  we  see  an  efibrt  made  by  the  system  (so  to 
speak)  to  get  rid  of  it,  in  those  cases  in  which  a  discharge  of  urinous 
fluid  takes  place  by  unusual  channels,  such  as  from  the  mucous  mem- 
brane of  the  stomach,  the  mamma,  the  umbilicus,  the  nose,  &c.,  when 
the  usual  secreting  action  of  the  Kidney  has  been  suspended.  Although 
the  accounts  of  such  cases  have  been  treated  with  ridicule  by  some 
Physiologists,  yet  there  seems  no  valid  reason  to  discredit  them,  when 
it  is  borne  in  mind  that,  in  persons  who  have  died  from  the  complete 
suspension  of  the  secretion,  effusions  containing  urea  have  been  found 
in  the  serous  cavities  of  the  trunk,  and  in  the  ventricles  of  the  brain. 
The  poisonous  influence  of  an  accumulation  of  urea  in  the  blood,  when 
strongly  exerted,  produces  in  the  first  instance  irregular  or  convulsive 
movements,  which  are  dependent  upon  irritation  of  the  Spinal  system 
of  nerves ;  then  loss  of  consciousness,  depending  upon  the  suspension  of 
the  powers  of  the  Brain ;  and  lastly,  complete  suspension  of  the  powers 
of  the  spinal  system,  so  that  the  ordinary  reflex  actions  cease,  and  life 
becomes  extinct  from  the  stoppage  of  the  respiratory  movements  (§  688). 
There  is  reason  to  believe,  that  many  convulsive  motions,  for  which  no 
obvious  cause  can  be  assigned,  have  their  origin  in  a  disordered  condi- 
tion of  the  blood,  resulting  from  imperfect  elimination  of  Urea ;  thus  it 
has  been  ascertained  that,  in  several  cases  of  puerperal  convulsions, 
urea  was  present  in  the  blood;  the  functional  power  of  the  kidney 
being  diminished  by  chronic  disease.  It  is  especially  to  be  noticed, 
that  most  of  the  cases  in  which,  the  urinary  secretion  is  discharged 
through  some  irregular  channel,  occur  in  persons  who  have  been  sub- 
ject to  those  convulsive  affections,  which  are  commonly  designated  as 
hysterical ;  and  that  the  discharge  of  a  large  quantity  of  urine  through 
the  natural  channel,  is  often  the  termination  of  an  hysterical  paroxysm. 
It  is  desirable,  therefore,  that  in  all  such  obscure  cases,  the  state  of  the 
urinary  secretion  should  be  carefully  looked  to. 

4.    Of  the  Cutaneous  and  Intestinal  Glandulce. 

742.  The  Glandulse  which  are  disposed  in  the  substance  of  the  Skin, 
and  in  the  walls  of  the  Intestinal  canal,  although  individually  minute, 
make  up  by  their  aggregation  an  excreting  apparatus  of  no  mean  im- 
portance.    The  Skin  is  the  seat  of  two  processes  in  particular ;  one  of 


CUTANEOUS  GLANDULiE,  417 


Ihich  is  destined  to  free  the  blood  of  a  large  quantity  of  fluid ;  and 
le  other  to  draw  off  a  considerable  amount  of  solid  matter.     To  effect 
lese  processes,  we  meet  with  two  distinct  classes  of  glandulae  in  its 
substance ;  the  Sudoriparous  or  sweat-glands ;  and  the  Sebaceous  or  oil- 
glands.     They  are  both  formed,  however,  upon  the  same  simple  plan ; 
and  can  frequently  be  distinguished  only  by  the  nature  of  their  secreted 
^^^roduct. 

^^B  743.  The  Sudoriparous  or  perspiratory  glandulae  form  small  oval  or 
^^lobular  masses,  situated  just  beneath  the  cutis,  in  almost  every  part  of 
the  surface  of  the  body.  Each  is  formed  by  the  convolution  of  a  single 
tube ;  which  thence  runs  towards  the  surface  as  the  efferent  duct, 
making  numerous  spiral  turns  in  its  passage  through  the  skin,  and 
penetrating  the  epidermis  rather  obliquely,  so  that  its  orifice  is  covered 
by  a  sort  of  little  valve  of  scarf-skin,  which  is  lifted  up  as  the  fluid 
issues  from  it  (Fig.  130).      The  convoluted  knot,  of  which  the  gland 

Fig.  130. 


The  anatomy  of  the  Skin :— 1.  The  Epidermis,  showing  the  oblique  laminae  of  which  it  is  composed,  and 
the  imbricated  disposition  of  the  ridges  upon  its  surface.  2.  The  Rete  Mucosum,  or  deep  layer  of  the  epi- 
dermis. 3.  Two  of  the  quadrilateral  papillary  clumps,  such  as  are  seen  in  the  palm  of  the  hand  or  sole  of 
the  foot;  they  are  composed  of  minute  conical  papillse.  4>  The  deep  layer  of  the  cutis,  the  Corium.  i.  Adi- 
pose cells.  6.  A  Sudoriparous  gland  with  its  spiral  duct,  such  as  is  seen  id  the  palm  of  the  hand  or  sole  of 
the  foot.  7.  Another  Sudoriparous  gland  with  a  straighter  duct,  such  as  is  seen  in  the  scalp.  8.  Two 
hairs  from  the  scalp,  enclosed  in  their  follicles;  their  relative  depth  in  the  skin  is  preserved.  9.  A  pair  of 
Sebaceous  glands,  opening  by  short  ducts  into  the  follicle  of  the  hair. 

consists,  is  copipusly  supplied  with  blood-vessels.  On  the  palm  of  the 
hand,  the  sole  of  the  foot,  and  the  extremities  of  the  fingers,  the  aper- 
tures of  the  perspiratory  ducts  are  visible  to  the  naked  eye,  being  situ- 
ated at  regular  distances  along  the  little  ridges  of  sensory  papillae,  and 
giving  to  the  latter  the  appearance  of  being  crossed  by  transverse  lines. 
According  to  Mr.  Erasmus  Wilson,  as  many  as  3528  of  these  glandulae 
exist  in  a  square  inch  of  surface  on  the  palm  of  the  hand ;  and  as  every 
tube,  when  straightened  out,  is  about  a  quarter  of  an  inch  in  length,  it 
follows  that  in  a  square  inch  of  skin  from  the  palm  of  the  haiid,  there 
exists  a  length  of  tube  equal  to  882  inches,  or  73J  feet.     The  number 

27 


418  \         OF  SECRETION. 

^  \ 

of  glandulse  in  other  parts^  of  the  skin  is  sometimes  greater,  but  gene- 
rally less  than  this ;  and,  according  to  Mr.  Wilson,  about  2800  may  be 
taken  as  the  average  number  of  pores  in  each  square  inch  throughout 
the  body.  Now  the  number  of  square  inches  of  surface,  in  a  man  of 
ordinary  stature,  is  about  2500;  the  number  of  pores,  therefore,  is 
seven  millions  ;  and  the  number  o*:  inches  of  perspiratory  tubing  would 
thus  be  1,750,000,  or  145,833  feet,  or  48,611  yards,  or  nearly  28 
miles,  \ 

744.  From  this  extensive  system  of  ^landulae,  a  secretion  of  watery 
fluid  is  continually  taking  place ;  and  a  considerable  amount  of  solid 
matter  also  is  drawn  off  by  the  epithelium-cells  that  line  the  tubuli. 
Under  ordi'tiary  circumstances,  the  fluid  is  carried  off  in  the  state  of 
vapour,  forming  the  insensible  perspiration ;  and  it  is  only  when  its 
amount  is  considerably  increased,  or  when  the  surrounding  air  is  already 
so  loaded  with  moisture  as  to  be  incapable  of  receiving  more,  that  the 
fluid  remains  in  the  form  of  sensible  perspiration  upon  the  surface  of 
the  skin.  It  is  difficult  to  estimate  the  proportion  of  solid  matter  con- 
tained in  this  secretion ;  partly  on  account  of  the  great  variations  in 
the  amount  of  fluid  eliminated  by  the  Sudoriparous  glands,  which  are 
governed  by  the  temperature  of  the  skin ;  and  partly  because  the  secre- 
tion can  scarcely  be  collected  for  analysis  free  from  the  sebaceous  and 
other  matters  which  accumulate  on  the  surface  of  the  skin.  According 
to  Anselmino  it  varies  from  J  to  IJ  per  cent.  ;  and  consists  in  part  of 
lactic  acid,  to  which  the  acid  reaction  and  sour  smell  of  the  secretion 
are  due ;  in  part  of  a  proteine-compound,  which  is  probably  furnished  by 
the  epithelium-cells  that  line  the  tubes ;  and  in  part  of  saline  matters, 
directly  proceeding  from  the  serum  of  the  blood.  Urea  has  been  re- 
cently detecte*^  in  the  perspiration  of  the  inhabitants  of  warm  climates. 

745.  The  amount  of"  fluid  excreted  from  the  skin  is  almost  entirely 
dependent  upon  the  temperature  of  the  surrounding  medium ;  being  in- 
creased with  its  rise,  and  diminished  with  its  fall.  The  object  of  this 
variation  is  very  evident ;  being  the  regulation  of  the  temperature  of 
the  body.  When  the  surface  is  exposed  to  a  high  degree  of  external 
heat,  the  increased  amount  of  fluid  set  free  from  the  perspiratory  glands 
becomes  the  means  of  keeping  down  its  own  temperature ;  far  this  fluid 
is  then  carried  off  in  a  state  of  vapour,  as  fast  as  it  is  set  free ;  and 
in  its  change  of  form,  it  withdraws  a  large  quantity  of  caloric  from  the 
surface.  But  if  the  hot  atmosphere  be  already  loaded  with  vapour,  this 
cooling  power  cannot  be  exerted ;  the  temperature  of  the  body  is  raised, 
and  death  supervenes,  if  the  experiment  be  long  continued.  The  cause 
of  the  increased  secretion  is  probably  to  be  looked  for  in  the  increased 
determination  of  blood  to  the  skin,  which  takes  place  under  the  stimulus 
of  heat; — The  entire  loss  by  Exhalation  from  the  lungs  and  skin,  during 
the  twenty-four  hours,  seems  to  average  a  little  above  2  lbs.  In  a  warm 
•dry  atmosphere,  however,  it  has  been  found  to  rise  to  as  much  as  51b. 
whilst  in  a  cold  damp  one,  it  may  be  lowered  to  If  lb.  Of  this  quantity, 
the  pulmonary  exhalation  is  usually  somewhat  less  than  one-third,  and 
tho  cutaneous  somewhat  more  than  two-thirds  ;  but  when  the  quantity 
of  fluid  lost  is  unusually  great,  the  increase  must  be  chiefly  in  the  Cuta- 
neous exhalation ;  since,  as  already  pointed  out  (§  701),  the  amount  of 


^  CUTANEOUS  EXHALATION.  419 

exhalation  from  the  lungs  is  not  influenced  by  the  external  tempera- 
ture, but  only  by  the  degree  in  which  the  surrounding  air  is  previously 
saturated  with  moisture. 

746.  The  variations  in  the  amount  of  fluid  set  free  by  Cutaneous 
and  Pulmonary  Exhalation,  are  counterbalanced  by  the  regulating 
action  of  the  Kidney  ;  which  allows  a  larger  proportion  of  water  to  be 
strained  ofi"  in  a  liquid  state  from  the  blood-vessels,  as  the  Exhalation 
is  less, — and  vice  versd.  The  Cutaneous  and  Urinary  excretions  seem 
to  be  vicarious,  not  merely  in  regard  to  the  amount  of  fluid  which  they 
carry  ofi"  from  the  blood,  but  also  in  respect  to  the  solid  matter  which 

^Khey  eliminate  from  it.  It  appears  that  at  least  100  grains  of  eff*ete 
^Hbzotized  matter  are  daily  thrown  ofi"  from  the  skin ;  and  any  cause 
^Birhich  checks  this  excretion,  must  increase  the  labour  of  the  Kidneys, 
^Bpr  produce  an  accumulation  of  noxious  matter  in  the  blood.  Hence 
^Battention  to  the  functions  of  the  skin,  at  all  times  a  matter  of  great 
importance,  is  peculiarly  required  in  the  treatment  of  Urinary  diseases  ; 
and  it  will  be  often  found  that  no  means  is  so  useful  in  removing  the 
lithic  acid  deposit,  as  copious  ablution  and  friction  of  the  skin,  com- 
bined with  exercise.  When  the  Exhalant  action  of  the  skin  is  com- 
pletely checked  by  the  application  of  an  impermeable  varnish,  the  efilsct 
is  not  (as  might  be  anticipated)  an  elevation  of  the  temperature  of  the 
body ;  on  the  contrary  it  is  lowered,  in  consequence,  as  it  would  appear, 
of  the  interruption  to  the  aeration  of  the  blood  through  the  skin,  which 
is  a  function  of  such  importance  in  the  lower  animals  (§  671),  and  of 
no  trifling  account  in  Man ;  and  in  a  short  time,  a  fatal  result  ensues. 
A  partial  suppression  by  the  same  means  gives  rise  to  febrile  symptoms, 
and  to  Albuminuria,  or  escape  of  the  albuminous  part  of  the  liquor 
sanguinis  into  the  urinary  tubes,  in  consequence  (it  would  appear)  of 
the  increased  determination  which  then  takes  place  towards  the  Kid- 
neys. These  facts-  are  interesting,  as  throwing  light  upon  the  febrile 
disturbance  which  accompanies  those  cutaneous  diseases  that  aff*ect  the 
whole  surface  of  the  skin  at  once,  and  interfere  with  its  functions ;  and 
as  partly  accounting  also  for  the  Albuminuria  which  frequently  mani- 
fests itself  during  their  progress,  especially  in  Scarlatina. 

747.  The  Skin  is  likewise  furnished  with  numerous  Sebaceous  glands, 
which  are  distributed  more  or  less  closely  over  the  whole  surface  of  the 
body ;  being  least  abundant  where  the  Perspiratory  glandulae  are  most 
numerous ;  and  vice  versd.  They  are  altogether  absent  on  the  palms  of 
the  hands  and  the  soles  of  the  feet ;  and  ar^  particularly  frequent  in  the 
skin  of  the  face  and  in  the  scalp.  They  diff'er  greatly  in  size  and  in  de- 
gree of  complexity ;  sometimes  consisting  of  short  straight  follicles ;  some- 
times closely  resembling  the  Sudoriparous  glandulae,  the  tubes,  however, 
being  usually  straighter  and  wider ;  and  being  sometimes  much  more 
complex  in  structure,  consisting  of  a  number  of  distinct  sacculi  clustered 
around  the  extremity  of  a  common  duct,  into  which  they  open,  and  form- 
ing little  arborescent  masses  about  the  size  of  millet-seeds.  In  some  situa- 
tions they  acquire  still  greater  complexity.  Thus  the  Meibomian  glan- 
dulae, which  are  found  at  the  edges  of  the  eyelids,  and  which  secrete  an 
unctuous  matter  for  their  lubrication,  are  long  sacculi  branching  out  at 
the  sides  (Fig.  Ill) ;  and  the  glandulae  of  the  ear  passage,  which  secrete 


420  OF   SECRETION. 

its  cerumen  or  waxy  matter,  and  wliich  belong  to  the  general  Sebaceous 
system,  are  formed  of  long  tubes,  highly  contorted,  and  copiously  sup- 
plied with  blood-vessels.  In  the  hairy  parts  of  the  skin,  we  usually 
find  a  pair  of  Sebaceous  follicles  opening  into  the  passage  through 
which  every  hair  ascends  (Fig.  130,  9).  The  purpose  of  the  sebaceous 
secretion  is  evidently  to  prevent  the  skin  from  being  dried  and  cracked 
by  the  influence  of  the  sun  and  air.  It  is  much  more  abundant  in  those 
races  of  mankind  which  are  formed  to  exist  in  warm  climates,  than  in 
the  races  that  naturally  inhabit  cold  countries ;  and  the  former  are 
accustomed  to  aid  its  preservative  power,  by  lubricating  their  skin  with 
vegetable  oils  of  various  kinds  ;  which  process  they  find  to  be  of  use,  in 
protecting  it  from  the  scorching  influence  of  the  solar  rays. — The  Seba- 
ceous follicles  are  frequently  the  residence  of  a  curious  parasite,  the 
Demodex  follioulorum,  which  is  stated  by  Mr.  Erasmus  Wilson  to  be 
present  in  great  numbers  in  the  skin  of  almost  all  inhabitants  of  large 
towns;  the  activity  of  their  cutaneous  glandular  system  being  much 
checked,  by  the  want  of  free  exposure  to  pure  air,  and  by  inert  habits  of 
life. 

748.  To  what  extent  the  Sebaceous  secretion  can  be  regarded  as 
destined  to  free  the  Blood  from  deleterious  matters,  it  may  not,  perhaps, 
be  very  easy  to  say ;  but  with  regard  to  the  functions  of  the  Skin  taken 
altogether,  as  a  channel  for  the  elimination  of  morbific  matters  from  the 
blood,  it  is  probable  that  they  have  been  much  underrated ;  and  that 
much  more  use  might  be  made  of  it  in  the  treatment  of  diseases, — 
especially  of  such  as  depend  upon  the  presence  of  some  morbific  matter 
in  the  circulating  current, — than  is  commonly  thought  advisable.  We 
see  that  Nature  frequently  uses  it  for  this  purpose ;  a  copious  perspira- 
tion being  often  the  turning-point  or  crisis  of  febrile  diseases,  removing 
the  cause  of  the  malady  from  the  blood,  and  allowing  the  restorative 
powers  free  play.  Again,  certain  forms  of  Rheumatism  are  charac- 
terized by  copious  acid  perspirations ;  and  instead  of  endeavouring  to 
check  these,  we  should  rather  encourage  them,  as  the  best  means  of 
freeing  the  blood  from  its  undue  accumulation  of  lactic  acid.  And  it 
is  recorded  that  in  the  "sweating  sickness,"  which  spread  throughout 
Europe  in  the  16th  century,  no  remedies  seemed  of  any  avail  but 
diaphoretics ;  which,  aiding  the  powers  of  nature,  concurred  with  them 
to  purify  the  blood  of  its  morbific  matter.  The  hot-air  bath,  in  some 
cases,  and  the  wet  sheet  (which,  as  used  by  the  Hydropathists,  is  one 
of  the  most  powerful  of  all  diaphoretics),  will  be  probably  employed 
more  extensively  as  therapeutic  agents,  in  proportion  as  the  importance 
of  acting  on  the  Skin,  as  an  extensive  collection  of  glandulse,  comes  to 
be  better  understood.  The  absurdity  of  the  "Hydropathic"  treatment 
consists  in  its  indiscriminate  application  to  a  great  variety  of  diseases ; 
no  person  who  has  watched  its  operation,  can  deny  that  it  is  a  remedy  of 
a  most  powerful  kind  ;  and  if  its  agency  be  fairly  tested,  there  is  strong 
reason  to  believe,  that  it  will  be  found  to  be  the  most  valuable  curative 
means  we  possess  for  various  specific  diseases,  which  depend  upon  the 
presence  of  a  definite  "materies  morbi"  in  the  blood,  especially  Gout 
and  chronic  Rheumatism ;  as  well  as  for  that  depressed  state  of  the 


CUTANEOUS   EXHALATION.  421 

general  system,  which  results  from  the  "wear  and  tear"  of  the  bodily 
and  mental  powers. 

749.  The  Mucous  surface  of  the  Alimentary  Canal  is  furnished,  like 
the  skin,  with  a  vast  number  of  glandulae,  varying  in  complexity,  from- 
the  simple  follicle,  to  a  mass  consisting  of  numerous  lobules  opening 
into  a  common  excretory  duct.  The  functions  of  these,  as  already 
pointed  out,  are  equally  various.  The  simple  follicles  appear  destined, 
for  the  most  part,  to  secrete  the  protective  mucus,  which  intervenes 
between  the  membranous  Wall  and  the  substances  contained  in  the 
canal,  and  which  serves  to  protect  the  former  from  the  irritating  action 
of  the  latter.  The  more  complex  follicles  of  the  Stomach  elaborate 
the  Gastric  fluid,  which  is  the  prime  agent  in  the  digestive  process 
(§  496).  The  still  more  elaborate  glandulae  of  Brunner,  situated  in  the 
walls  of  the  duodenum,  also  seem  to  furnish  a  product  which  is  con- 
cerned in  the  digestive  operation  (§  480).  But  there  is  strong  reason 
to  believe,  that  the  function  of  the  Peyerian  glan dulse,  which  beset  the 
walls  of  the  lower  part  of  the  intestinal  canal,  is  purely  excretory  ;  and 
that  they  are  destined  to  eliminate  putrescent  matters  from  the  blood, 
and  to  convey  them,  by  the  readiest  channel,  completely  out  of  the 
body.  That  the  putrescent  elements  of  the  faeces  are  not  immediately 
derived  from  the  food  taken  in,  so  much  as  from  the  secreting  action  of 
the  intestinal  glandulae,  appears  from  this  consideration  ; — that  faecal 
matter  is  still  discharged,  ejen  in  considerable  quantities,  long  after 
the  intestinal  tube  has  been  completely  emptied  of.  its  alimentary  con- 
tents. We  see  this  in  the  course  of  many  diseases,  when  food  is  not 
taken  for  many  days,  during  which  time  the  bowels  are  completely 
emptied  of  their  previous  contents  by  repeated  evacuations  ;  and  what- 
ever then  passes,  must  be  derived  from  the  intestinal  walls  themselves. 
Sometimes  a  copious  flux  of  putrescent  matter  continues  to  take  place 
spontaneously ;  whilst  it  is  often  produced  by  the  agency  of  purgative 
medicine.  The  "  colliquative  diarrhoea,"  which  frequently  comes  on 
at  the  close  of  exhausting  diseases,  and  which  usually  precedes  death 
by  starvation,  appears  to  depend,  not  so  much  upon  a  disordered  state 
of  the  intestinal  glandulae,  as  upon  the  general  disintegration  of  the 
solids  of  the  body,  which  calls  them  into  extraordinary  activity,  for  the 
purpose  of  separating  the  decomposing  matter. 

750.  Thus  we  perceive,  that  we  have  here,  also,  to  watch  for  the 
indications  of  Nature ;  and  that  this  extensive  /  system  of  intestinal 
glandulae,  being  the  principal  channel  for  the  elimination  of  putrescent 
matters  from  the  blood,  should  be  especially  attended  to,  when  there 
is  reason  to  think  that  such  matters  are  present  in  too  large  an  amount. 
Hence,  when  diarrhoea  is  already  existing,  we  may  often  do  more  good 
by  allowing  it  to  take  its  course,  or  even  by  increasing  it  by  the  agency 
of  purgative  medicines,  than  by  attempting  to  check  it,  and  thus 
causing  the  retention  of  the  morbid  matter  in  the  circulating  current. 
But,  on  the  other  hand,  it  is  necessary  to  bear  in  mind  the  extreme 
irritability  of  the  intestinal  mucous  membrane  ;  and  carefully  to  avoid 
exciting  it,  when  it  is  already  in  excess,  or  when  there  is  danger  that 
it  will  supervene, — as  in  that  form  of  Fever  in  which  there  is  a  peculiar 


422  OF   SECRETION. 

liability  to  inflammation  and  ulceration  of  the  walls  of  the  alimentary 
canal,  and  of  their  contained  glandulse. 

5.   General  Summary  of  the  Excreting  Processes. 

751.  We  have  now  passed  in  review  the  various  processes,  by  which 
the  products  of  the  disintegration  of  the  animal  tissues  are  carried 
off;  and  we  have  seen  that  the  necessity  for  their  removal  is  much 
more  urgent  than  for  their  replacement.  A  cold-blooded  animal  may 
subsist  for  some  weeks,  or  even  months,  without  a  fresh  supply  of  food, 
the  waste  of  its  tissues  being  so  small,  if  it  remain  in  a  state  of  rest,  as 
to  be  quite  compatible  with  the  continuance  of  its  life ;  and  a  warm- 
blooded animal  may  live  for  many  days  or  even  weeks,  provided  that  it 
has  in  its  body  a  store  of  fat  sufficient  to  keep  up  its  heat  by  the  com- 
bustive  process.  But  in  either  case,  if  the  exhalation  of  carbonic  acid 
by  the  lungs,  the  elimination  of  biliary  matter  by  the  liver,  the  separa- 
tion of  urea  or  uric  acid  by  the  kidneys,  or  the  withdrawal  of  putrescent 
matter  by  the  intestinal  glandulae,  be  completely  checked,  a  fatal  result 
speedily  ensues ; — more  speedily  in  warm-blooded  animals,  than  in  those 
which  cannot  sustain  a  high  independent  temperature,  on  account  of 
the  greater  proneness  to  decomposition  in  the  bodies  of  the  former,  than 
in  those  of  the  latter ; — and  more  speedily  in  the  latter,  when  their 
bodies  are  kept  at  an  elevated  temperature  by  the  warmth  of  the  sur- 
rounding medium,  than  when  the  degree  of  heat  is  so  low,  that  there  is 
little  proneness  to  spontaneous  change  in  the  substance  of  their  bodies. 

752.  It  may  be  taken  as  a  general  principle,  in  regard  to  the  Ex- 
creting processes  (including  Respiration),  that  they  have  a  threefold 
purpose ; — in  the  first  place,  to  carry  off  the  normal  results  of  the  waste 
or  disintegration  of  the  solid  tissues,  and  of  the  decomposition  of,  the 
fluids ; — in  the  second  place,  to  draw  off  the  superfluous  alimentary 
matter,  which  though  received  into  the  circulating  current,  is  not  con- 
verted into  solid  tissue,  in  consequence  of  the  want  of  demand  for  it ; . 
— and  in  the  third  place,  to  carry  off  the  abnormal  products,  which 
occasionally  result  from  irregular  or  morbid  changes  in  the  system. 
Thus  by  the  Lungs  are  excreted  a  large  amount  of  carbon,  and  some 
hydrogen,  resulting  from  the  disintegration  of  the  tissues,  especially 
the  nervous  and  muscular ;  the  same  elements,  in  animals  that  take  in  a 
large  proportion  of  farinaceous  or  oleaginous  aliment,  may  be  derived  im* 
mediately  from  the  food,  with9ut  any  previous  conversion  into  solid  tissue ; 
and  there  can  be  little  doubt  that  the  respiratory  function  is  also  an  impor- 
tant means  of  purifying  the  blood  from  various  deleterious  matters, 
either  introduced  from  without  (such  as  narcotic  poisons),  or  generated 
within  the  body  (such  as  the  poison  of  fever).*  And  it  is  important 
to  bear  this  last  circumstance  in  mind ;  since  it  enables  us  to  understand 
how,  if  time  be  given,  the  system  frees  itself  from  such  noxious  sub- 
stances ;  and  points  out  the  duty  of  the  medical  attendant  to  be  rather  that 

*  There  is  strong  reason  to  believe  that,  in  many  instances,  a  small  amount  of  poi- 
sonous matter  introduced  from  without,  in  the  form  of  a  contagion  Or  miasm,  may  lead, 
by  a  process  resembling  fermentation,  to  the  production  of  a  large  quantity  of  similar 
noxious  substances  in  the  animal  fluids. 


GENERAL   RELATIONS   OF   EXCRETING  PROCESSES.  423 

of  supporting  the  powers  of  the  body  by  judiciously-devised  means,  and 
of  aiding  the  elimination  of  the  morbid  matter  through  the  lungs  and 
skin  by  a  copious  supply  of  pure  air,  than  of  interfering  more  actively 
to  promote  that  which  Nature  is  already  effecting  in  the  niost  advanta-- 
geous  manner. 

753.  In  like  manner,  the  Liver  is  charged  with  the  separation  of 
hydrocarbon,  in  a  fluid  form ;  for  which  a  supply  of  oxygen  is  not 
requisite.  This  product  is  partly  derived  from  the  waste  of  the  sys- 
tem ;  but  the  arrangement  of  the  biliary  vessels  leads  to  the  belief,  that 
part  of  it  may  be  at  once  derived  from  crude  matter,  taken  up  by  the 
mesenteric  veins,  and  eliminated  from  them  by  the  hepatic  cells,  with- 
out ever  passing  into  the  general  circulation.  And  various  facts  seem 
to  indicate,  that  the  Liver  is  also  destined  to  remove  from  the. blood 
extraneous  substances,  which  are  noxious  to  it.  Thus,  in  cases  where 
death  has  resulted  from  the  prolonged  introduction  of  the  salts  of  Cop- 
per into  the  system,  a  considerable  amount  of  that  metal  has  been  ob- 
tained from  the  substance  of  the  gland. 

754.  It  has  been  already  pointed  out  (§  726),  that  in  those  tribes  of 
animals  whose  respiration  is  feeble,  a  considerable  part  of  the  mass  of 
the  liver  is  composed  of  fatty  matter ;  and  this  condition  may  be  in- 
duced, as  a  state  of  disease,  in  warm-blooded,  energetically-respiring 
Birds  and  Mammals,  by  impediments  to  the  due  performance  of  the 
respiratory  process.  This  is  remarkably  shown  in  the  treatment  of  the 
geese  which  are  to  furnish  the  celebrated  Strasburg  pates.  The  unfor- 
tunate bird  is  closely  confined  at  a  high  temperature ; 

so  that  the  respiration  is  reduced  to  its  minimum  amount,  ,  Fig- 131. 
by  the  combined  effects  of  warmth  and  muscular  inac- 
tion ;  and  it  is  then  crammed  with  maize,  which  contains 
a  large  amount  of  oily  matter.  The  consequence  is,  that 
its  liver  soon  enlarges,  and  becomes  unusually  fatty ;  its 
cells  being  gorged  with  oil-globules,  instead  of  each  con-        Hepatic  ceiis 

...  xi  ^  1    -x  •      /I  J  gorged  with  Fat: 

tammg  no  more  than  one  or  two :  and  it  is  then  ready     —  a,  atrophied 
for  the  epicureans  who  set  so  high  a  value  on  the  patS     pose  gioi)uies^  ^* 
de  foie  gras.     A  similar  diseased  condition  of  the  liver 
frequently   presents   itself  in   Man,   in   connexion   with   chronic   dis- 
orders of  the  respiratory  organs,  which  diminish  the  amount  of  hydro- 
carbon eliminated  through  their  agency ;  this  "fatty  liver"  is  peculiarly 
common  in  the  advanced  stages  of  Phthisis.      Jt  may  arise,  however, 
from  a  local   disorder  of  nutrition,  such  as  that  which  produces  the 
fatty  degeneration  of  other  organs.     Such  a  fatty  degeneration  may 
occur  in  the  Kidney,  for  example,  as  a  consequence  of  inflammation  of 
its  tissues. 

T55.  With  regard  to  the  Kidneys,  it  has  been  already  pointed  out 
that  they  are  the  special  emunctories  of  the  azotized  products  of  the 
decomposition  of  the  tissues  ;  and  that  they  serve  also  to  convey  away 
the  overplus  of  such  earthy  and  alkaline  salts,  as  are  readily  soluble. 
Moreover,  it  has  been  shown  that  the  surplus  proteine-compounds, 
which  are  not  required  for  the  nutrition  of  the  system,  must  be 
excreted  by  their  agency,  after  having  been  metamorphosed  into  urea. 
And  we  have  now  to  notice,  that  other  matters  of  an  injurious  charac- 


424  OP  SECRETION. 

ter,  whether  introduced  from  without,  or  generated  within  the  system, 
are  drawn  off  bj  the  same  channel.  Thus  the  saline  compounds,  taken 
up  by  the  absorbent  process  (§  493),  are  for  the  most  part  set  free 
through  these  organs ;  especially  when  their  properties  are  such,  as  to 
excite  the  action  of  the  kidneys  in  a  peculiar  degree.  Thus,  Prussiate 
of  Potash  has  been  detected  in  the  urine,  within  one  minute  after  it 
has  been  introduced  into  the  stomach.  It  has  been  sometimes  noticed 
that  Iodide  of  Potassium,  when  administered  as  a  medicine,  is  retained 
within  the  body  for  some  days,  producing  extensive  cutaneous  erup- 
tions, or  some  other  unusual  consequence  ;  and  that  it  then  suddenly 
begins  to  pass  off  by  the  kidneys,  and  is  excreted  in  very  large  quan- 
tities. Further,  it  has  been  shown  by  Dr.  Letheby,  that  poisonous 
substances  (such  as  arsenious  acid),  introduced  into  the  system  in 
small  but  frequently-repeated  doses,  may  be  carried  out  of  the  body 
with  such  rapidity  as  to  be  prevented  from  exerting  their  injurious 
effects,  provided  that  diuretics  be  administered  at  the  same  time.  The 
effect  of  the  inhalation  of  the  vapour  of  turpentine,  even  in  a  very 
diluted  state,  in  speedily  imparting  to  the  urine  the  odour  of  violets,  is 
an  evidence  that  not  merely  the  actual  substances  imbibed,  but  new  and 
peculiar  compounds  to  which  they  give  rise,  are  thus  eliminated  by  the 
Kidneys. 

756.  The  most  singular  variations  in  the  excretory  function  of  the 
Kidneys  are  seen,  however,  when  the  Urine  is  charged  with  substances 
which  are  not  only  foreign  to  it,  but  are  altogether  foreign  to  the 
healthy  body.  The  most  remarkable  instance  of  this  is  seen  in  the 
disease  termed  Diabetes,  in  which  a  large  quantity  of  Sugar  is  formed, 
either  directly  from  the  food,  or  by  the  disintegration  of  the  solid 
tissues ;  and  in  which  this  compound  is  eliminated  by  the  Kidneys, 
imparting  to  the  urine  a  saccharine  taste.  And  another  example  of  • 
the  same  general  fact  is  seen  in  the  "  oxalic  diathesis,"  in  which  an 
unusual  arrangement  of  the  elements  that  usually  form  urea  or  uric 
acid,  gives  rise  to  a  new  and  peculiar  compound,  oxalate  of  ammonia ; 
this  being  drawn  off  by  the  kidneys,  and  being  decomposed  by  the 
calcareous  matter  present  in  the  urine,  gives  rise  to  a  deposit  of  oxalate 
of  lime.  In  the  treatment  of  such  diseases,  our  attention  must  be  given, 
not  so  much  to  the  secreting  organ,  as  to  the  condition  of  the  system  at 
large,  of  which  the  character  of  the  secreted  product  is  the  indication 
or  exponent. 

757.  To  what  has  already  been  stated  in  regard  to  the  exhalant 
functions  of  the  Lungs  and  Skin,  it  may  be  added  that  many  states  of 
disease  are  marked  by  an  unusual  odour  emitted  from  the  body ;  and 
there  can  be  little  doubt  that  the  peculiar  odorous  matter  is  pre-formed 
in  the  blood, — as  we  know  that  the  ordinary  scent  of  any  species 
(whether  Man,  Dog,  Horse,  Goat,  &c.)  may  be  set  free  from  the  blood 
of  that  species,  by  the  addition  of  sulphuric  acid.  The  existence  of 
such  odours,  therefore,  is  not  to  be  attributed  to  disordered  function  in 
the  excreting  organs ;  but  to  the  formation  of  morbid  products  in  the 
interior  of  the  body,  which  these  organs  do  their  best  to  remove.  The 
foetid  breath,  which  frequently  accompanies  an  attack  of  indigestion,  is 
another  instance  of  the  power  of  the  lungs  to  eliminate,  not  merely 


HEAT  OF  ANIMALS  AND   PLANTS.  425 

Carbonic  acid,  but  other  products  of  the  changes  in  composition  which 
the  food  undergoes  when  introduced  into  the  system. 

758.  The  same  remarks  apply,  and  with  yet  greater  force,  to  the 
Intestinal  glandulge ;  whose  function  it  is,  not  merely  to  remove  the- 
putrescent  matter  ordinarily  formed  by  the  disintegration  of  the  tis- 
sues, or  by  the  decomposition  of  unassimilated  food,  but  also  to  draw 
off  the  still  more  offensive  products  of  such  changes  as  take  place  in 
disease.  Thus  there  are  conditions  of  the  system,  in  which,  without 
any  well-marked  disorder,  the  faeces  emit  a  peculiarly  foetid  odour ; 
and  with  these  is  almost  always  associated  a  depressed  state  of  mind. 
Now  it  can  scarcely  be  doubted,  that  the  real  fault  is  here  rather  in 
the  early  part  of  the  nutritive  operations,  than  in  the  excretory  func- 
tion ;  and  that  the  foetor  of  the  contents  of  the  intestine  depends  upon 
the  undue  formation  of  putrescent  matter  in  the  system,  which,  by  taint- 
ing the  blood,  causes  its  action  upon  the  brain  to  become  unhealthy. 
The  object  of  the  physician  will  be  here  to  eliminate  the  morbid 
product,  by  the  moderate  use  of  purgatives ;  and  so  to  regulate  the  diet 
and  regimen,  as  to  correct  the  tendency  to  its  formation. — An  exces- 
sive foetor  in  the  evacuations,  as  well  as  in  the  exhalations  from  the 
skin  and  lungs,  is  peculiarly  characteristic  of  those  very  severe  forms 
of  typhus  (now,  happily,  of  comparatively  rare  occurrence),  which  are 
termed  putrid  fevers.  Here  the  whole  of  the  solids  and  fluids  of  the 
body  appear  to  have  an  unusual  tendency  to  decomposition,  in  conse- 
quence of;  the  introduction  of  some  morbid  agent,  which  acts  as  a  fer- 
ment ;  and  the  system  attempts  to  free  itself  from  the  products  of  that 
decomposition,  by  the  various  organs  of  excretion,  particularly  the  Skin 
and  Intestinal  surface. 

759.  It  is  of  great  importance  that  the  Student  should  form  clear 
conceptions  on  this  subject;  and  that  he  should  not  (as  too  often  hap- 
pens), by  directing  his  remedies  to  the  mere  symptoms  or  results  of  a 
disease,  act  in  precise  opposition  to  the  natural  tendency  of  the  system 
to  free  itself  from  some  unusual  noxious  matter,  through  those  channels 
which  are  ordinarily  destined  to  carry  off  only  the  regular  products  of 
its  disintegration. 


CHAPTER  X. 

OF   THE   DEVELOPMENT   OP  HEAT,   LIGHT,   AND   ELECTRICITY,   IN  THE 

ANIMAL  BODY. 

760.  It  has  been  shown,  in  an  earlier  part  of  this  volume  (chap,  ii.), 
that  all  Vital  actions  require  a  certain  amount  of  Heat  for  their  per- 
formance;  and  that  there  is  a  great  variety  amongst  the  different 
classes  of  Animals,  both  in  regard  to  the  degree  of  Heat  which  is  most 
favourable  to  the  several  processes  of  their  economy,  and  in  regard  to 
their  own  power  of  sustaining  it,  independently  of  oscillations  in  the 


426  DEVELOPMENT  OF  HEAT,   ETC. 

temperature  of  the  surrounding  medium.  As  a  general  rule,  the 
Invertebrated  animals  are  cold-blooded;  that  is,  they  have  little  or  no 
power  of  sustaining  an  independent  temperature.  The  degree  of 
energy  of  their  vital  actions  entirely  depends,  therefore,  upon  the 
warmth  they  receive  from  the  air  or  water  they  inhabit ;  they  have  no 
power  of  resisting  the  depressing  influence  of  cold ;  and  they  are  gene- 
rally so  organized,  as  to  pass  into  a  state  of  complete  inaction  or  torpi- 
dity, when  the  temperature  sinks  below  a  certain  point, — after  gradu- 
ally becoming  more  arid  more  inert  with  every  diminution  in  the  heat 
of  their  bodies.  The  same  is  true,  also,  of  most  Fishes  and  Reptiles : 
but  the  animals  of  the  former  class,  from  the  more  equable  temperature 
of  the  medium  they  inhabit,  are  not  so  liable  to  be  reduced  to  inaction 
as  the  latter ;  being  usually  so  organized,  as  to  retain  their  activity  so 
long  as  the  water  around  them  continues  liquid;  and  being  actually 
imbedded  in  a  frozen  state,  when  the  water  around  them  is  converted 
into  ice,  without  the  loss  of  their  vitality.  There  are  certain  Fishes, 
however, — such  as  the  Thunny,  Sword-fish,  and  other  large  species  of 
the  Mackerel  tribe, — which  are  able  to  sustain  a  temperature  consi- 
derably above  that  of  the  sea  they  inhabit ;  thus  in  the  Bonito,  the 
heat  of  the  body  has  been  found  to  be  99°,  when  the  temperature  of 
the  surrounding  sea  was  but  80J°.  It  is  not  probable,  however,  that 
the  temperature  of  the  body  would  be  kept  up  to  the  same  standard, 
if  that  of  the  sea  should  be  considerably  lowered ;.  but  it  would  proba- 
bly remain  at  from  18°  to  20°  above  the  latter.  And  in  like  manner, 
it  has  been  noticed  that  many  of  the  more  active  Reptiles  possess  the 
power  of  sustaining  the  temperature  of  their  bodies  at  10°  or  15°  above 
that  of  the  surrounding  air. 

761.  The  classes  of  animals  which  are  especially  endowed  with  the 
power  of  producing  and  maintaining  heat,  are  Insects,  Birds,  and 
Mammalia.  The  remarkable  variations  which  present  themselves  in 
the  temperature  of  the  first  of  these  classes,  and  the  connexion  of  these 
variations  with  the  condition  of  the  animals  in  regard  to  activity  or 
repose,  have  already  been  sufl&ciently  noticed  (§  123). — The  tempera- 
ture of  Birds  is  higher  than  that  of  any  other  class  of  animals ;  varying 
from  100°  to  111°  or  112°.  The  lowest  degree  is  found  in  some  of  the 
aquatic  species,  as  the  Gull,  and  in  those  which  principally  live  on  the 
ground,  as  the  Fowl  tribe ;  and  the  highest  in  the  birds  of  most  active 
flight,  as  the  Swallow.  The  temperature  of  the  Mammalia  seems  to 
range  from  about  96°  to  104° ;  that  of  Man  has  been  observed  as  low 
as  96|°,  and  as  high  as  102°.  The  variations  are  dependent  in  part 
upon  the  temperature  of  the  external  air ;  but  are  influenced  also  by 
the  general  condition  of  the  body  as  to  repose  or  activity,  the  period  of 
the  day,  the  time  that  has  elapsed  since  a  meal,  &c.  A  somewhat 
larger  amount  of  caloric  is  generated  during  the  day,  than  in  the  night ; 
and  the  body  is  usually  warmer,  by  a  degree  or  two,  at  noon,  than  at 
midnight.  There  is  also  a  slight  increase  during  the  digestion  of  a 
meal ;  and  exercise  is  a  powerful  means  of  raising  the  temperature. — 
The  range  of  temperature  is  much  greater  in  disease ;  thus  the  thermo- 
meter has  been  seen  to  rise  to  106°  in  Scarlatina  and  Typhus,  and  to 


HEAT   OF  ANIMALS   AND   PLANTS.  427 

110J°  in  Tetanus  ;  whilst  it  has  fallen  to  82°  in  Spasmodic  Asthma,  and 
to  77°  in  Cyanosis  and  Asiatic  Cholera. 

762.  In  searching  for  the  conditions  on  which  this  production  of  heat 
within  the  Animal  hody  is  dependent,  it  is  very  important  to  bear  in 
mind,  that  a  similar  generation  of  Caloric  may  be  observed  in  the  Vege- 
table kingdom.  It  appears  from  the  most  recent  and  exact  experi- 
ments, that  all  living  Plants  are  somewhat  warmer  than  similar  dead^ 
phdrits  exposed  to  the  same  atmosphere ;  and  that  the  elevation  is  the 
greatest  in  the  leaves  and  young  stems,  in  which  the  most  active  vital 
changes  are  taking  place.  But  the  most  decided  production  of  heat 
occurs  in  the  flowering  of  certain  Plants,  such  as  the  Arum,  which 
have  large  fleshy  receptacles,  on  which  a  great  number  of  blossoms  are 
crowded ;  thus  a  thermometer  placed  in  the  centre  of  five  spadixes  of 
the  Arum  cordifolium  has  been  seen  to  rise  to  111°,  and  one  placed  in 
the  midst  of  twelve  spadixes  has  risen  to  121°,  whilst  the  temperature 
of  the  surrounding  air  was  only  QQ°.  In  the  germination  of  seeds,  also, 
a  great  elevation  of  temperature  occurs,  which  is  rendered  most  evident 
by  bringing  together  a  number  of  seeds,  as  in  the  process  of  malting^  so 
that  the  caloric  is  not  dissipated  as  fast  as  it  is  generated ;  the  ther- 
mometer, placed  in  the  midst  of  a  mass  of  seeds  in  active  germination, 
has  been  seen  to  rise  to  110°. 

763.  Thus  it  is  evident  that  the  chemical  changes  which  are  involved 
in  the  operations  of  Nutrition,  are  capable  of  setting  free  a  large  amount 
of  heat ;  which,  although  ordinarily  dissipated  from  the  vegetating  sur- 
face too  speedily  to  manifest  itself,  becomes  sensible  enough,  when  this 
rapid  loss  is  checked.  If  we  further  examine  into  the  nature  of  the 
chemical  changes  which  appear  most  concerned  in  this  elevation  of 
temperature,  we  find  that  they  uniformly  consist  in  the  combination  of 
the  carbon  of  the  plant  with  the  oxygen  of  the  atmosphere  ;  so  that  a 
large  quantity  of  carbonic  acid  is  formed  and  set  free,  precisely  in  the 
manner  of  the  Respiration. of  Animals.  This  process  is  so  slowly  per- 
formed, in  the  ordinary  growth  of  Plants,  that  it  is  concealed  (as  it 
were)  by  the  converse  change, — the  fixation  of  carbon  from  the  carbonic 
acid  of  the  atmosphere,  under  the  influence  of  light  (§  83).  But  it  takes 
place  with  extraordinary  energy  during  flowering  and  germination ;  a 
large  quantity  of  carbon  being  set  free,  by  union  with  the  oxygen  of  the 
air ;  and  the  starchy  matter  of  the  receptacle,  or  of  the  seed,  being  con- 
verted into  sugar.  Now  it  has  been  ascertained  by/careful  experiments, 
that  the  amount  of  heat  generated  is  in  close  relation  with  the  amount 
of  carbonic  acid  set  free ;  and  that,  if  the  formation  of  the  latter  be  pre- 
vented, by  placing  the  flower  or  the  seed  in  nitrogen  or  hydrogen,  no 
elevation  of  temperature  takes  place ;  whilst,  if  the  process  be  stimu- 
lated by  pure  oxygen,  so  that  a  larger  proportion  of  carbonic  acid  is 
evolved,  the  elevation  of  temperature  is  more  rapid  and  considerable 
than  usual. 

764.  Upon  examining  into  the  conditions  under  which  Caloric  is  gene- 
rated in  the  Animal  body,  we  find  them  essentially  the  same.  Wherever 
the  temperature  of  the  body  is  maintained  at  a  regular  standard,  so  as 
to  be  independent  of  variations  in  the  warmth  of  the  surrounding  me- 
dium, we  find  a  provision  for  exposing  the  blood  most  freely  to  the  in- 


423  ANIMAL   HEAT. 

fluence  of  oxygen,  and  for  extricating  its  carbonic  acid ;  thus  in  Birds 
and  Mammals,  the  blood  is  distributed,  in  a  minute  capillary  network, 
on  the  walls  of  the  pulmonary  air-cells,  the  gaseous  contents  of  which 
are  continually  renewed ;  and  in  Insects,  the  air  is  carried  into  every. 
part  of  the  body  by  the  ramifying  tracheae.  We  constantly  find  a  pro- 
portion between  the  amount  of  heat  evolved,  and  that  of  carbonic  acid 
generated ;  this  is  peculiarly  evident  in  Insects,  whose  respiration  and 
calorification  vary  so  .  remarkably  (§  123);  but  it  is  also  proved  by 
comparing  the  amount  of  carbonic  acid  generated  by  warm-blooded  ani- 
mals, when  the  external  temperature  is  low,  and  when  more  heat  must 
be  evolved  to  keep  the  temperature  of  their  bodies  up  to  its  proper  stan- 
dard, with  that  generated  by  the  same  animals  in  a  warmer  atmosphere, 
when  the  proper  animal  heat  is  diminished  in  amount  (§  691). 

765.  The  sources  of  the  Carbonic  Acid  thrown  ofi*  by  the  lungs,  have 
been  already  pointed  out  (chap,  viii.)  r  it  is  partly  derived  from  the 
metamorphosis  of  the  tissues ;  but  partly,  in  all  but  purely  carnivorous 
animals,  more  directly  from  the  non-azotized  portion  of  the  food.  The 
precise  mode  in  which  the  carbon  thus  supplied  is  united  with  the  oxy- 
gen derived  from  the  atmosphere,  is  not  yet  known  ;  but  it  is  certain  that, 
in  whatever  manner  the  combination  may  take  place,  a  certain  measure 
of  caloric  must  be  generated.  It  appears,  however,  from  various  ex- 
periments, that  the  whole  quantity  of  caloric  generated  by  an  animal  in 
a  given  time,  is  greater  than  that  which  would  be  evolved  by  the  com- 
bustion of  the  carbon,  included  in  the  carbonic  acid  evolved  during  the 
same  time.  Hence  it  is  evident  that  other  chemical  processes  occurring 
within  the  body  are  concerned  in  the  maintenance  of  the  temperature ; 
and  it  is  not  difficult  to  point  to  some  of  these.  It  is  probable,  in  the  first 
place,  that  some  of  the  Hydrogen  of  the  food  may  be  "burned  off"  by 
union  with  the  oxygen  of  the  atmosphere,  so  as  to  form  part  of  the 
water  which  is  exhaled  from  the  lungs.  Again,  the  sulphur  and  phos- 
phorus of  the  food  are  converted,  by  oxygenation,  into  sulphuric  and 
phosphoric  acids  ;  in  which  process,  heat  must  be  generated.  In  the 
composition  of  urea,  moreover,  oxygen  is  present  in  much  larger  propor- 
tion, than  it  is  in  the  proteine-compounds  by  the  metamorphosis  of  which 
it  is  formed ;  so  that  in  its  production  too,  caloric  will  be  generated.  In 
fact  it  may  be  stated  as  a  general  truth,  that  the  whole  excess  of  the  oxy- 
gen absorbed,  over  that  which  is  contained  in  the  carbonic  acid  exhaled 
(§  689),  must  be  applied  to  purposes  in  the  laboratory  of  the  system,  in 
which  caloric  will  be  disengaged.  Still,  the  amount  of  Carbonic  Acid 
exhaled  must  always  be  the  measure  of  the  chemical  processes,  by  which 
heat  is  generated  in  the  body;  because  it  is  itself  the  result  of  the 
chief  of  these  processes  (the  union  of  carbon  and  oxygen),  and  because 
the  surplus  amount  of  oxygen  which  is  absorbed,  and  which  is  applied 
to  other  purposes,  is  closely  related  to  it. 

766.  The  power  of  maintaining  a  high  independent  temperature  is 
usually  much  less  in  young  warm-blooded  animals,  than  in  adults. 
There  are  considerable  variations  in  this  respect,  however,  amongst 
different  species ;  for  where  the  young  animal  is  born  in  such  an  ad- 
vanced condition,  as  to  be  thenceforth  almost  independent  of  parental 
assistance,  it  is  capable  of  maintaining  its  own  temperature ;  but  where 


BEQULATION   OF   HEAT   IN   MAN.  429 


^^rent  for  some  time,  it  is  also  more  or  less  der;:;ndent  upoja  the  warmth 
imparted  to  it  from  the  parental  body.  This  is  peculiarly  the  case  with 
the  young  of  the  Human  species,  which  is  longer  dependent  upon 
parental  aid,  than  that  of  any  other  animal.  In  the  case  of  children 
born  very  permaturely,  the  careful  sustenance  of  their  heat  is  one  of 
the  points  most  to  be  attended  to  in  rearing  them ;  and  even  the  most 
vigorous  infants,  born  at  the  full  time,  are  far  from  being  able  to  keep 
up  their  proper  standard  without  assistance,  if  exposed  to  a  cool  atmo- 
sphere. It  has  been  ascertained  that,  during  the  first  month  of  infant 
life,  the  mortality  in  winter  is  nearly  double  that  of  summer,— being 
1*39  in  January  to  0*78  in  July ;  and  this  striking  difference  cannot  be 
attributed  to  any  other  cause,  than  the  injurious  influence  of  external 
cold,  which  the  calorifymg  powers  of  the  infant  do  not  enable  it  to 
resist.  As  age  advances,  the  power  of  generating  heat  increases,  and 
the  body  becomes  much  more  independent  of  external  vicissitudes  ;  so 
that;  in  adult  life,  the  winter  mortality  is  to  that  of  summer,  only  as 
1*05  to  0-91,  or  less  than  one-sixth  more.  In  advanced  age,  the  calori- 
fying  power  again  diminishes ;  and  this  we  should  anticipate  from  the 
general  torpor  of  the  nutritive  operations  in  old  persons.  Between  50 
and  65  years  of  age,  the  relative  winter  and  summer  mortality  are 
nearly  as  in  the  first  month  of  infancy ;  and  at  90  years,  the  average 
mortality  of  winter  is  much  more  than  twice  that  of  summer,  being  as 
1-58  to  0-64. 

767.  It  appears  that  there  is  a  difference  in  calorifying  power,  not 
merely  at  different  ages,  but  at  different  seasons :  the  amount  of  heat 
generated  in  summer  not  being  sufficient,  in  many  animals,  to  prevent 
the  body  from  being  cooled  down  by  prolonged  exposure  to  a  tempera- 
ture, which  is  natural  to  them  in  winter.  To  what  extent  this  is  the 
case  with  Man,  it  is  difficult  to  say.  His  constitution  is  distinguished 
by  its  power  of  adapting  itself  to  circumstances ;  and  he  can  live  under 
extremes  of  temperature  more  wide  than  those,  which  most  other  ani- 
mals can  endure  (§  113).  Whether  in  the  torrid  zone,  or  in  the  arctic 
regions,  he  can  maintain  his  healthy  condition  under  favourable  circum- 
stances ;  in  each  case  his  natural  appetite  leading  him  to  the  use  of 
that  kind  and  amount  of  food,  which  is  best  suited  to  the  wants  of  his 
system.  But  the  longer  he  has  been  habituated  to  a  very  warm  or  a 
very  cold  climate,  the  more  difficult  he  at  first  finds  it  to  live  comforta- 
bly in  one  of  an  opposite  character ;  as  his  constitution,  having  become 
adapted  to  one  particular  set  of  circumstances,  requires  time  to  accom- 
modate itself  to  an  opposite  one. 

768.  The  means  by  which  the  heat  of  the  body  is  prevented  from 
rising  above  its  normal  standard,  even  in  the  midst  of  a  very  high  tem- 
perature in  the  surrounding  air,  are  of  the  most  simple  character.  The 
excreting  action  of  the  skin  is  directly  stimulated  by  the  application  of 
warmth  to  the  surface ;  and  the  fluid  which  is  poured  forth,  being  im- 
mediately vaporized,  converts  a  large  quantity  of  sensible  caloric  into 
latent,  and  thus  keeps  down  the  temperature  of  the  skin.  By  this  pro- 
vision, the  body  may  be  exposed  with  impunity  to  dr^  air  of  600°  or 
more,  so  long  as  the  supply  of  fluid  is  maintained.     But  it  cannot  long 


430  ANIMAL   LUMINOSITY. 

sustain  exposure  to  air  saturated  with  vapour,  even  though  it  may  not  be 
many  degrees  hotter  than  the  body ;  because  the  cooling  act  of  evapo- 
ration from  the  skin  cannot  then  be  carried  on. 

769.  The  evolution  of  Light  is  a  very  interesting  phenomenon,  chiefly 
witnessed  among  the  lower  animals,  and  usually  supposed  not  to  occur 
in  any  class  above  Fishes.  It  is  particularly  remarkable  among  the 
Kadiata  and  inferior  Mollusca.  A  large  proportion  of  the  Acalephce,  or 
Jelly-fish  tribe,  possess  the  property  of  luminousness  in  a  greater  or  less 
degree ;  and  it  is  to  small  animals  of  this  class,  which  sometimes  multi- 
ply to  an  amazing  extent,  that  the  beautiful  phenomenon  of  pJiosphores- 
cence  of  the  sea  is  chiefly  due.  In  the  midst  of  the  soft  diff'used  light 
thus  occasioned,  brilliant  stars,  ribands,  and  globes  of  fire  are  frequently 
seen;  these  appearances  being  due  to  the  luminosity  of  the  larger 
species  of  the  same  tribe,  or  to  that  of  other  marine  animals. — Some  of 
the  most  remarkable  examples  of  luminosity,  in  regard  to  the  brilliancy 
of  the  light  emitted,  occur  in  the  class  of  Insects.  Here  the  emission 
is  confined  to  one  portion  of  the  body.  Or  to  two  or  more  isolated  spots, 
instead  of  being  diff'used  over  a  larger  surface ;  and  it  is  proportionally 
increased  in  intensity.  The  phenomenon  of  Animal  Luminousness 
appears  usually  attributable  to  the  formation  of  a  peculiar  secretion ; 
which,  in  many  instances,  continues  to  shine  after  removal  from  the 
animal,  so  long  as  it  is  exposed  to  the  influence  of  oxygen :  and  it 
seems  not  unreasonable  to  believe,  that  it  depends  upon  a  slow  process 
of  combustion,  analogous  to  that  which  takes  place  when  phosphorus  is 
exposed  to  the  air.  There  is  a  special  provision  in  Insects,  for  convey- 
ing a  large  supply  of  air  through  the  peculiar  substance,  which  is  depo- 
sited beneath  the  luminous  spots  ;  and  the  power  which  Glow-worms,  Fire- 
flies, &c.,  possess,  of  suddenly  extinguishing  their  light  and  as  suddenly 
renewing  it,  seems  to  depend  upon  their  control  over  the  air-aperture  or 
spiracle  by  which  air  is  admitted,  the  stoppage  of  the  supply  of  air 
causing  the  immediate  cessation  of  the  luminousness,  and  its  readmission 
occasioning  a  renewal  of  the  process  on  which  it  depends. — It  is  proba- 
ble, however,  that  in  certain  cases  the  luminosity  is  rather  of  an  electrical 
character.  There  are  several  of  the  smaller  Annelida  or  marine  Worms, 
which  are  brilliantly  luminous  when  irritated ;  the  luminosity  having  the 
character,  however,  of  a  succession  of  sparks,  rather  than  of  a  steady 
glow.  It  appears  from  the  experiments  of  M.  Quatrefages,  that  this  pecu- 
liar luminosity  is  the  especial  attribute  of  the  muscular  system ;  and  that 
it  is  produced  with  every  act  of  muscular  contraction  in  these  animals. 

770.  Although  no  such  luminosity  is  commonly  manifested  in  any  of 
the  higher  Yertebrata,  or  in  Man,  yet  there  are  well-authenticated 
cases,  in  which  the  phenomenon  has  presented  itself  in  the  living  Human 
subject,* — luminous  emanations  from  dead  animal  matter  being  of  no 
unfrequent  occurrence.  In  most  of  these  cases,  however,  the  indivi- 
duals exhibiting  the  luminosity  had  suff'ered  from  consumption,  or  some 
other  wasting  disease,  and  were  near  the  close  of  their  lives  at  the 
time ;  so  that  it  is  probable  that  a  decomposition  of  the  tissues  was 

*  See  an  account  of  several  cases  of  the  Evolution  of  Light  in  the  Living  Human 
Subject,  bj  Sir  Henry  Marsh,  M.D.,  M.R.LA,,  &c. 


I 


ANIMAL   ELECTRICITY. — ELECTRIC  FISHES.  431 


actually  in  progress,  analogous  to  that  which,  when  it  occurs  after 
death,  imparts  luminosity  to  the  decaying  body.  One  instance  is 
recorded,  in  which  a  large  cancerous  sore  of  the  breast  emitted  light 
enough  to  enable  the  hands  on  a  watch-dial  to  be  distinctly  seen  when 
it  was  held  within  a  few  inches  of  the  ulcer ;  here,  too,  decomposition 
was  obviously  going  on,  and  the  phosphorescent  matter  produced  by  it 
was  exposed  to  the  oxygenating  action  of  the  atmosphere. 

771.  Slight  manifestations  of  free  Electricity^  or,  in  other  words, 
disturbances  of  Electric  equilibrium,  are  very  frequent  in  living  ani- 
mals ;  and  they  are  readily  accounted  for,  when  we  bear  in  mind  that 
nearly  all  chemical  changes  are  attended  with  some  alteration  in  the 
electric  state  of  the  bodies  concerned ;  and  when  we  consider  the  num- 
ber and  variety  of  such  changes  in  the  living  animal  body.  When  slight, 
however,  they  can  only  be  detected  by  refined  means  of  observation ; 
and  it  is  only  when  they  are  considerable,  that  they  attract  notice. 
The  most  remarkable  examples  of  the  evolution  of  free  Electricity  in 
Animals,  are  to  be  found  in  certain  species  of  the  class  of  Fishes;  the 
best  known  of  which  are  the  Torpedo  or  Electric  Ray,  and  the  G-ym- 
notus  or  Electric  Eel.  These  possess  organs,  in  which  Electricity  may 
be  generated  and  accumulated  in  large  quantities,  and  from  which  it 
may  be  discharged  at  will.  The  shock  of  a  large  and  vigorous  Gym- 
notus  is  sufficiently  powerful  to  kill  small  animals,  and  to  paralyse  large 
ones,  such  as  men  and  horses ;  that  of  the  Torpedo  is  less  severe,  but 
it  is  sufficient  to  benumb  the  hand  that  touches  it. 

772.  The  electric  organs  of  the  Torpedo  (which,  from  being  found 
on  European  shores,  has  been  the  most  studied)  are  of  flattened  shape, 
and  occupy  the  front  and  sides  of  the  body ;  forming  two  large  masses, 
which  extend  backwards  and  outwards  from  each  side  of  the  head. 
They  are  composed  of  two  layers  of  membrane  s.eparated  by  a  consi- 
derable space;  and  this  space* is  divided  by  vertical  partitions  into 
hexagonal  cells  like  those  of  a  honeycomb,  the  ends  of  which  are 
directed  towards  the  two  surfaces  of  the  body.  These  cells,  which  are 
filled  with  a  whitish  soft  pulp,  somewhat  respmbling  the  substance  of 
the  brain,  but  containing  more  water,  are  again  subdivided  horizon- 
tally by  membranous  partitions  ;  and  all  these  partitions  are  profusely 
supplied  with  blood-vessels  and  nerves. — The  electrical  organs  of  the 
Gymnotus  are  essentially  the  same  in  structure ;  but  they  difi'er  in 
shape,  in  accordance  with  the  conformation  of  th'e  animal. — In  these, 
and  the  other  Electrical  fishes,  the  electric  organs  are  supplied  with 
nerves  of  very  great  size,  larger  than  any  others  in  the  same  animals, 
and  larger  than  any  nerves  in  other  animals  of  similar  bulk.  These 
nerves  arise  from  a  peculiar  ganglionic  enlargement  of  the  Medulla 
Oblongata,  termed  the  electric  lobe,  and  seem  chiefly  analogous  to  the 
pneumogastrics  of  other  animals. 

773.  The  following  conditions  appear  to  be  essential  to  the  manifes- 
tation of  the  Electric  powers  of  these  animals.  Two  parts  of  the  body 
must  be  touched  at  the  same  time ;  and  these  two  must  be  in  different 
electrical  states.  The  most  energetic  discharge  is  procured  from  the 
Torpedo,  by  touching  its  back  and  belly  simultaneously ;  the  electricity 
of  the  back  being  positive,  and  that  of  the  belly  negative.     When  two 


432  ELECTRIC   FISHES — ELECTRICITY   OF   MUSCLES. 

parts  of  the  same  surface,  at  an  equal  distance  from  the  electric  organ, 
are  touched,  no  effect  is  produced,  as  they  are  equally  charged  with  the 
same  electricity ;  but  if  one  point  be  further  from  it  than  the  other, 
a  discharge  occurs,  the  intensity  of  which  is  proportioned  to  the  diffe- 
rence in  the  distance  of  the  points  from  the  electric  organ.  However 
much  a  Torpedo  is  irritated,  no  discharge  can  take  place  through  a 
single  point ;  but  the  fish  makes  an  effort  to  bring  the  border  of  the 
other  surface  in  contact  with  the  offending  body,  through  which  a  shock 
is  then  transmitted.  This,  indeed,  is  probably  the  usual  way  in  which 
the  discharge  is  effected. — The  identity  of  animal  with  common  Elec- 
tricity is  proved,  not  merely  by  the  similarity  of  the  effects  upon  the 
feelings  produced  by  the  shock  of  both;  but  also  by  the  fact  that  a 
spark  may  be  obtained,  and  chemical  decompositions  effected,  by  the 
former,  precisely  as  by  the  latter. 

774.  The  power  of  the  animal  over  the  actions  of  its  Electric  organs, 
is  dependent  upon  their  connexion  with  the  nervous  centres.  If  all 
the  nerve-trunks  supplying  the  organ  on  one  side  be  divided,  the  ani- 
mal's control  over  that  organ  will  be  destroyed;  but  the  power  of  the 
other  may  remain  uninjured.  If  the  nerves  be  partially  divided  on 
either  or  both  sides,  the  power  is  retained  by  the  portions  of  the  organs 
which  are  still  connected  with  the  centres  by  the  trunks  that  remain. 
Even  slices  of  the  organ,  entirely  separated  from  the  body  except  by  a 
nervous  fibre,  may  exhibit  electrical  properties.  Discharges  may  be 
produced,  by  irritating  the  part  of  the  nervous  centres  from  which  the 
trunks  proceed,  so  long  as  the  latter  are  entire ;  or  by  irritating  the 
portions  of  the  divided  trunks  which  remain  in  connexion  with  the 
electric  organs ;  or  even  by  irritating  portions  of  the  electric  organs 
themselves,  when  separated  from  the  nervous  centres. — In  all  these 
respects,  there  is  a  strong  analogy  between  the  action  of  the  nerves  on 
the  Electric  organs,  and  their  action  on  the  Muscles.  The  connexion 
of  the  organs  specially  appropriated  to  each  of  these  actions  with  the 
Nervous  system,  the  dependence  of  their  functions  upon  the  integrity  of 
this  connexion  and  upon  the  state  of  activity  of  the  central  organs, 
the  influence  of  stimulation  applied  to  the  nervous  centres  or  trunks, 
the  results  of  ligature  or  section  of  the  nerve,  and  the  effects  of  poi- 
sonous agents,  are  all  so  remarkably  analogous  in  the  two  cases,  that 
it  seems  scarcely  possible  to  doubt  that  the  Nervous  force  is  the  agent 
which  is  instrumental  in  producing  both  sets  of  phenomena.  Still, 
however,  no  proof  whatever  can  be  derived  from  this  source,  of  the 
identity  of  nervous  influence  with  any  form  of  Electricity  ;  since  all  that 
Can  be  legitimately  inferred  from  it  is,  that  Nerve-force  acting  through 
a  particular  organic  structure  developes  Electricity,  in  virtue  of  the 
correlation  formerly  explained  (§  396). 

775.  It  is  another  interesting  point  of  analogy  between  the  action 
of  Muscles,  and  that  of  the  Electrical  organs,  that  the  former  (as  is 
now  fully  proved  by  the  elaborate  and  exact  researches  of  Matteucci) 
is  attended  with  electric  disturbance.  In  any  fresh  vigorous  muscle,  in 
a  state  of  passive  or  tonic  contraction,  there  is  a  continual  electric 
current  from  the  interior  to  the  exterior,  sufficient  to  excite  the  leg  of 
a  frog  to  energetic  contraction,  when  its  nerve  is  so  applied  to  the 


MANIFESTATIONS   OP  ELECTRICITY.  433 

^HQUScle,  as  to  receive  the  influence  of  this  current.  And  a  much  more 
^B)owerful  current  is  produced,  when  the  muscle  is  thrown,  by  a  stimu- 
^Hus  applied  to  its  own  nerve,  into  a  state  of  energetic  contraction.  The 
IRexplanation  of  the  constant  direction  of  the  current,  from  the  interior 
towards  the  exterior  of  the  muscle,  seems  to  be,  that  the  changes  con- 
nected with  the  nutrition  and  disintegration  of  the  muscular  tissue  go 
on  more  energetically  in  its  interior,  than  they  do  nearer  its  surface, 
where  the  proper  muscular  fibres  are  mingled  with  a  large  proportion 
of  areolar  and  tendinous  substance. 

776.  It  was  observed  by  Galvani  that  there  exists  in  the  Frog, 
during  its  whole  life,  a  continual  current  of  Electricity  passing  from 
its  extremities  towards  its  head;  and  as  no  such  current  has  been  detect- 
ed in  any  other  animal,  it  has  been  termed  the  courant  propre^  or  pe- 
culiar current,  of  the  Frog.  It  bears  this  curious  analogy  to  the  elec- 
tric discharges  of  Fishes, — that  it  is  not  manifested  if  the  connexion  be 
made  between  corresponding  points  of  the  opposite  sides,  but  that  it 
shows  itself  when  the  communication  is  made  between  points  higher  or 
lower  in  the  body,  whether  on  the  same  or  on  opposite  sides. — There 
now  seems  reason  to  believe,  however,  from  the  observations  of  Mat- 
teucci,  that  this  "  proper  current  of  the  frog"  is  but  a  special  case  of  the 
ordinary  muscular  current,  depending  upon  the  peculiar  arrangement  of 
the  muscular  and  tendinous  elements  in  this  animal.  Both  currents  are 
alike  influenced  by  agents  which  afi*ect  the  vitality  of  the  muscle  ;  and 
it  is  curious  that  poisoning  with  sulphuretted  hydrogen  should  almost 
immediately  put  an  end  to  each,  although  ordinary  narcotic  poisons 
have  very  little  influence. 

777.  Manifestations  of  Electricity  may  be  produced,  in  most  animals 
having  a  soft  fur,  by  rubbing  the  surface,  especially  in  dry  weather ; 
this  is  a  fact  sufficiently  well  known  in  regard  to  the  domestic  Cat. 
Some  individuals  of  the  Human  race  exhibit  spontaneous  manifestations 
of  electricity,  which  are  occasionally  of  very  remarkable  power.  There 
are  persons,  for  instance,  who  scarcely  ever  pull  off"  articles  of  dress 
that  have  been  worn  next  their  skin,  without  sparks  and  a  crackling 
noise  being  produced,  especially  in  dry  weather.  This  is  partly  due, 
however,  to  the  friction  of  these  materials  with  the  surface,  and  with 
each  other.  But  the  case  of  a  lady  has  been  recently  put  on  record, 
who  was  for  many  months  in  an  electric  state  so  different  from  that  of 
surounding  bodies,  that,  whenever  she  was  but  slightly  insulated  by  a 
carpet  or  othir  feebly-conducting  medium,  sparks  passed  between  her 
person  and  any  object  which  she  approached.  When  she  was  most 
favourably  circumstanced,  four  sparks  per  minute  would  pass  between 
her  finger  and  the  brass  ball  of  a  stove,  at  a  distance  of  1 J  inch.  Va- 
rious experiments  were  tried,  with  the  view  of  ascertaining  if  the  Elec- 
tricity was  produced  by  the  friction  of  articles  of  dress  ;  but  no  change 
in  these  seemed  to  modify  its  intensity.  From  the  pain  which  accom- 
panied the  passage  of  the  sparks,  this  condition  was  a  source  of  much 
discomfort  to  the  subject  of  it. 

28 


434  OF  GENERATION  AND  DEVELOPMENT. 

CHAPTER  XI. 

OP  GENERATION  AND  DEVELOPMENT. 
1.    General  View  of  the  Nature  of  the  Process. 

778.  There  is  no  one  of  the  functions  of  living  beings,  that  distin- 
guishes them  in  a  more  striking  and  evident  manner  from  the  inert 
bodies  which  surround  them,  than  the  process  of  Generation.  By  this 
function,  each  race  of  Plants  and  Animals  is  perpetuated ;  whilst  the 
individuals  composing  it  successively  disappear  from  the  surface  of  the 
earth,  by  that  death  and  decay  which  are  the  common  lot  of  all.  There 
are  certain  tribes,  in  which  the  death  of  the  parent  is  necessary  for  the 
liberation  of  the  germs  from  which  a  new  race  is  to  spring  up.  This 
is  the  case,  for  example,  in  some  of  the  simplest  Cellular  Plants ;  in 
which  every  cell  lives  for  itself  alone,  and  performs  its  whole  series  of 
vital  operations  independently  of  the  rest.  But  as,  in  more  complex 
organisms,  we  find  certain  cells  set  apart  for  Absorption,  others  for 
Secretion,  &c.,  so  do  we  find  a  particular  group  of  cells  set  apart  for 
Reproduction ;  and  these  go  through  a  series  of  changes  peculiar  to 
themselves,  without  interfering  with  the  general  life  of  the  structure. — 
It  is  in  the  Vegetable  kingdom,  that  the  essential  character  of  the  Ge- 
nerative process  can  be  best  studied ;  and  we  shall,  in  the  first  instance, 
therefore,  inquire  into  the  nature  and  import  of  the  principal  pheno- 
mena which  it  presents. 

779.  If  we  take  as  our  starting-point  the  simple  cell  in  which  the  in- 
dividuality of  the  lowest  Algae  seems  to  reside,  we  find  that  this  cell, 


Various  stages  of  deTelopment  of  EcBmatococcus  binalis  • — a,  a,  simple  rounded  cells ;  b,  elongated  cells, 
the  endochrome  preparing  to  divide;  c,  c,  cells  in  which  the  diyision  has  taken  place;  d,  cluster  of  four  cells 
formed  by  a  repetition  of  the  same  process. 

under  the  influence  of  light  and  warmth,  and  supplied  with  aliment, 
multiplies  itself  to  an  extent  that  almost  seems  unlimited ;  and  this  by 
a  process  of  duplication  exactly  analogous  to  that  which  has  been  al- 
ready described  (§  212)  as  taking  place  in  Cartilage  ; — the  chief  difie- 


I 


SIMPLEST   FORMS   OF   GENERATIVE   PROCESS. 


435 


rence  being,  that  in  the  latter  the  fission  commences  ill  the  nucleus,  each 
half  of  which  seems  to  draw  around  it  a  portion  of  the  contents  of  the 
cell,  whilst  in  the  former  the  fission  shows  itself  at  once  in  the  entire 
endochrome,  there  being  no  distinct  nucleus  (Fig.  132).  Now  although 
the  efi'ect  of  this  operation  is  to  produce  a  great  number  of  new  cells, 
yet  it  cannot  be  truly  considered  as  an  act  of  Generation ;  for  it  is  ob- 
viously analogous  to  that  multiplication  of  the  component  cells,  which 
takes  place  as  a  part  of  every  process  of  development  in  the  most  com-  • 
plex  organisms ;  the  only  difference  being,  that  the  new  cells  are  here 
in  great  degree  independent  one  of  another,  so  as  to  be  able  to  maintain 
heir  existence  when  isolated ;  whilst  among  the  higher  tribes,  there  is 
close  a  relation  of  mutual  dependence  between  the  component  cells, 
that  they  cannot  continue  to  live  if  separated  from  one  another.  And 
we  shall  hereafter  see,  that  the  early  development  of  the  embryonic 

Fig.  133. 


Successive  stages  of  development  of  simpler  Algae: — a,  individual  cells  of  Protococcus  viridis;  B,  c,  clusters 
formed  by  their  multiplication ;  D,  filament  of  Schizogonium  murale  ;  e,  a  similar  filament,  subdividing  late- 
rally, which  constitutes  the  early  form  of  the  Vlvacece;  F,  G,  portions  of  the  expanded  thallus  of  Ulvafurfur 
racea,  formed  by  the  continuance  of  the  same  process  of  transverse  subdivision. 

mass,  even  in  the  highest  Animals,  presents  phenomena  in  all  respects 
comparable  to  this  multiplication  of  the  simplest  Cellular  Plants  by 
successional  subdivision  (§  805) ;  all  the  descendants  of  the  original  cell, 
however,  here  remaining  in  mutual  apposition,  and  concurring  to  make 
up  what  is  commonly  designated  as  a  single  individual,  whilst  in  the 


436  OF  GENERATION  AND  DEVELOPMENT. 

simplest  Plants,  tiiese  cells,  as  their  number  is  successively  augmented 
by  fission,  are  more  and  more  widely  separated  from  each  other,  and 
may  disperse  themselves  over  an  extensive  surface. — If,  however,  they 
should  remain  in  connexion  with  each  other,  they  may  form  clusters, 
or  fronds  (expanded  leafy  surfaces),  according  to  the  direction  in  which 
the  subdivision  takes  place  (Fig.  133) ;  and  this  without  the  slightest 
departure  from  the  original  cellular  type,  which  is  preserved  throughout 
the  structure,  every  part  being  exactly  similar  to  every  other.  In  these 
composite  organisms,  we  usually  find  a  provision,  not  merely  for  the 
extension  of  the  original  structure,  but  for  the  multiplication  of  indivi- 
duals, which  being  still  referable  to  the  general  type  of  cell-subdivision, 
must  be  considered  as  a  process  of  development,  rather,  than  of  genera- 
tion. This  consists  in  the  emission,  from  the  interior  of  certain  of  the 
celJs,  of  broods  of  young  cells  formed  in  their  interior ;  and  these,  in 
the  lower  aquatic  plants,  are  very  commonly  furnished  with  cilia,  by 
the  agency  of  which  they  are  dispersed  through  the  water,  beginning 
to  develope  themselves  into  the  likeness  of  the  organisms  from  which 
they  sprang,  as  soon  as  their  movement  has  ceased.  These  "  zoo- 
spores," as  they  are  termed,  must  be  regarded  as  the  representatives  of 
the  gemmce  or  buds  of  higher  Plants.  The  latter  are  usually  developed 
in  continuity  with  the  stock  from  which  they  originate ;  but  there  are 
many  instances  in  which  they  are  spontaneously  detached ;  and  there 
are  few  cases  in  which  they  will  not  continue  their  existence  under 
favourable  circumstances,  when  artificially  separated  from  it,  as  is 
practised  in  the  operations  of  grafting,  budding,  &c. 

780.  The  true  Generative  process,  on  the  other  hand,  seems  to  con- 
sist, throughout  the  Vegetable  kingdom,  in  the  reunion  of  the  contents 
of  two  cells  which  have  been  separated  in  the  process  of  development 
and  multiplication,  and  in  the  production  of  a  germ  as  the  result  of  this 
reunion,  which  is  usually  very  different  in  its  characters  and  properties 
from  either  of  the  cells  whose  contents  have  contributed  to  form  it. 
This  process  has  been  observed  to  take  place  in  the  Vegetable  kingdom, 
under  three  principal  forms,  which  seem  to  be  characteristic  of  the 
lowest  Cryptogamia,  of  the  higher  Cryptogamia,  and  of  the  Phanero- 
gamia,  respectively. — The  first  of  these  presents  itself  in  those  simple 
Cellular  Plants,  in  which,  whether  the  cells  remain  in  connexion  or  not, 
their  endowments  are  all  of  the  same  nature.  At  a  certain  time  of  the 
year  (it  would  seem)  in  each  species,  the  cells  approach  one  another  in 
pairs,  and  their  endochromes  (or  coloured  contents)  are  intermingled 
(Fig.  134,  a),  either  by  the  rupture  of  both  cells  (1),  or  by  the  formation 
of  a  direct  communication  from  the  interior  of  one  to  that  of  the  other, 
in  which  case  the  union  of  the  two  endochromes  may  take  place  either 
in  the  connecting  channel  (2),  or  in  one  of  the  pairs  of  cells  (3).  Of 
this  process,  which  is  known  as  conjugation,  the  result  is  the  formation 
of  a  body  known  as  a  sporangium,  which  may  be  considered  as  the  first 
product  of  the  true  generative  process ;  and  from  this  sporangium  (which 
is  a  single  cell,  or  a  pair  or  cluster  of  cells)  a  "  new  generation"  is  de- 
veloped by  the  subsequent  process  of  fission  and  multiplication.  There 
is  here  no  definite  distinction  of  the  sexes,  the  conjugating  cells  being 
apparently  alike  in  their  endowments ;  such  a  distinction  is  shadowed 


SIMPLEST  FORMS   OF   GENERATIVE   PROCESS. 


437 


forth,  however,  where  the  sporangium  is  developed  within  one  of  them. 
— The  second  form  of  the  true  generative  process  is  seen  even  in  the 
higher  Algae ;  and,  although  the  extent  of  its  prevalence  has  not  yet 
been  clearly  determined,  it  is  probably  common  to  the  Liverworts^ 
Mosses,  and  Ferns,  it  being  in  the  last  of  these  groups  that  it  has  been 
most  satisfactorily  made  out.  In  conformity  with  the  separation  or 
specialization  of  organs  which  is  characteristic  of  these  Plants,  we  find 
that  the  Generative  power  is  now  limited  to  certain  small  parts  of  them, 
and  that  these  produce  two  orders  of  cells,  very  distinct  in  their  endow- 
ments, which  may  be  called  respectively  "  sperm-cells,"  and  "germ- 
cells."  It  is  from  the  latter  that  the  new  plant  originates ;  but  this  it 
can  only  do,  when  the  fertilizing  influence  of  the  former  has  been  con- 
veyed to  it ;  and  the  provision  for  this  purpose  is  very  remarkable. 
The  sperm-cells,  developed  within  bodies  termed  antheridia,  form  in 
their  interior,  as  their  characteristic  products,  minute  spirally-coiled 
filaments,  usually  furnished  with  cilia  at  one  extremity,  and  bearing  a 
very  close  resemblance  to  the  spermatozoa  of  animals  (§  785).  These, 
when  liberated  from  the  cells  within  which  they  w^ere  formed,  possess  a 
very  active  power  of  movement,  in  virtue  of  which  they  #iake  their  way 
to  the  germ-cells ;  and  when  they  have  impinged  against  these,  there  is 
reason  to  believe  that  they  dissolve  away,  and  that  the  product  of  their 
diffluence  is  absorbed  into  the  germ-cells  and  mingles  with  the  contents 
of  the  latter,  the  formation  of  a  germ  being  the  result  of  this  intermix- 
ture (Fig.  134,  b).     Here,  then,  we  have  the  distinction  of  sexes  well 


Diagram  representing  the  three  principal  forms  of  the  Generative  process  in  Plants: — A,  conjugation  of 
inferior  Cryptogamia;  formation  of  the  sporangium,  h,  by  admixture  of  the  discharged  endochromes  of  the 
parent-cells,  a,  a;  2,  production  of  the  sporangium,  6,  within  a  dilatation  formed  by  the  union  of  the  twa 
parent-cells;  3,  production  of  the  sporangium,  h,  by  the  passage  of  the  endochrome  of  cell  a  into  that  of  cell 
a*,  marking  out  a  sexual  difference. — b.  fertilization  of  germ  in  higher  Cryptogamia;  a,  sperm-cell  discharge 
ing  its  spiral  filament,  a*,  germ-cell,  against  which  one  of  these  filaments  is  impinging,  b,  germ  produced 
by  their  contact. — c,  fertilization  of  germ  in  Phanerogamia;  a,  germ-cell,  or  pollen-grain,  sending  its  pro- 
longed tube  down  the  style,  until  it  reaches  a*  the  germ-cell,  inclosed  in  the  ovule,  the  section  of  whose 
coats  is  shown  at  c ;  from  the  contact  of  the  two,  is  produced  the  germ,  &. 

marked ;  but  both  sperm-cells  and  germ-cells  are  usually  developed  in 
the  same  organism,  and  are  alike  the  product  of  a  single  original  germ. 
Throughout  the  Cryptogamic  series,  the  fertilized  germ  appears  to  be 


438  OF  aENERATION  AND  DEVELOPMENT. 

thrown  at  once  upon  the  world,  and  is  dependent  for  its  supply  of  food 
upon  its  own  absorbing  and  assimilating  powers ;  these  enable  it  to  mul- 
tiply itself  by  fission,  sometimes  to  a  vast  extent ;  and  thus  an  elaborate 
and  complex  organism  (such  as  a  Tree-fern)  may  be  produced. — In  the 
third  form  of  the  generative  process,  which  is  peculiar  to  Phanerogamia 
(or  Flowering  Plants),  there  is  the  same  distinction  between  "sperm- 
cells"  and  "  germ-cells  ;"  but  the  mode  in  which  the  action  of  the  former 
upon  the  latter  is  brought  about,  is  very  different.  The  "sperm-cell," 
which  is  known  as  the  pollen-grain,  and  is  developed  in  the  anthers  of 
the  flower,  does  not  here  evolve  self-moving  filaments,  but,  when  it  falls 
upon  the  apex  of  the  style,  puts  forth  long  tubes,  which  insinuate  them- 
selves down  between  its  loosely-connected  tissue,  until  they  reach  the 
ovary  at  its  base.  Here  they  meet  with  the  ovules,  which  are  in  reality 
"  germ-cells"  imbedded  in  a  mass  of  nutriment  stored  up  by  the  parent ; 
and  the  pollen-tube,  entering  the  micropyle  or  foramen  of  the  ovule, 
penetrates  into  such  close  approximation  to  the  germ-cell  contained 
"within  it,  that  its  contents  find  a  ready  passage  by  endosmose  into  the 
latter  (Fig.  134,  c).  Here  again,  therefore,  we  have  the  same  essential 
phenomenon,— •he  intermixture  of  the  contents  of  the  sperm-cell  and 
of  the  germ-cell,  as  the  condition  for  the  development  of  the  true  germ. 
But  this  germ,  still  making  its  first  appearance  as  a  single  cell  within 
the  ovule,  is  supplied  with  nutriment  by  its  parent ;  and  this  not  merely 
whilst  the  ovule  remains  in  connexion  with  the  organism  which 
evolved  it,  but  for  some  time  subsequently,  the  store  laid  up  around  it 
in  the  seed  being  the  material  at  the  expense  of  which  its  early  deve- 
lopment takes  place.  It  is  not,  in  fact,  until  its  true  leaves  have  been 
evolved  and  its  root-fibres  have  penetrated  the  soil,  which  takes  place 
in  the  act  of  germination,  that  it  becomes  capable  of  absorbing  and 
assimilating  nutriment  for  itself.  As  soon,  however,  as  this  takes 
place,  the  young  plant  becomes  independent  of  further  assistance ;  and 
all  its  subsequent  growth  is  provided  for  by  its  own  powers.  In  pro- 
cess of  time,  its  generative  apparatus  is  evolved ;  and  here,  too,  we  find, 
that  the  two  sets  of  sexual  organs  are  usually  developed  in  the  same 
organism,  it  being  only  a  small  proportion  of  Phanerogamia  that  are 
dioecious,  i.  e.,  that  have  the  male  or  staminiferous  flowers,  and  the 
female  or  pistilline,  restricted  to  difierent  individuals.* 

781.  The  history  of  embryonic  Development  in  Flowering  Plants, 
presents  some  interesting  points  of  correspondence  with  that  of  the 
higher  Animals. — The  germ  that  is  developed  within  the  germ-cell 
(here  designated  the  "embryonic  vesicle"  of  the  ovule)  as  the  product 
of  the  admixture  of  its  contents  with  those  of  the  sperm-cell  (or  pollen- 
grain),  is  itself  a  single  cell ;  and  the  early  history  of  its  development 
closely  resembles  that  which  may  be  observed  in  all  the  inferior  Plants. 
In  the  first  place  it  subdivides  into  two,  each  of  these  into  two  others, 
and  so  on ;  its  first  nisus  or  tendency  being  to  the  production,  not  of 
the  parts  which  are  to  be  evolved  into  the  stem,  roots,  leaves,  &c.,  of  the 
perfect  plant,  but  of  a  leaf-like  expansion,  which  may  be  likened  to  the 

*  For  a  more  particular  account  of  the  recent  discoveries,  on  which  the  above  ac- 
count of  the  Generation  of  Plants  is  based,  see  the  Author's  *' Principles  of  General 
and  Comparative  Physiology,"  chap,  xviii.,  sect.  2. 


SIMPLEST   FORMS   OF   GENERATIVE   PROCESS.  439 

frond  of  the  Cryptogamia,  and  of  which  the  function  is  only  temporary. 
It  is  by  this  organ,  the  single  or  double  cotyledon,  that  the  nourishment 
provided  in  the  ovule  is  absorbed  and  prepared  for  the  development  of 
the  young  Plant ;  the  permanent  fabric  of  which,  even  at  the  time  of 
the  maturity  of  the  seed,  forms  but  a  small  proportion  of  the  entire 
embryonic  structure.  In  the  act  of  germination,  however,  the  perma- 
nent portions  are  developed  at  the  expense  of  the  temporary,  the  plu- 
mula  and  radicle  absorbing  the  nourishment  which  has  been  elaborated 
by  the  cotyledons  ;  and  having  fulfilled  its  transient  purpose,  and  com- 
pleted its  term  of  life,  the  first  leaf-like  expansion  withers  and  dies. 
The  tissues  of  the  young  Plant  are  at  first  of  the  simplest  possible 
character ;  but  as  the  organs  characteristic  of  its  adult  condition  are 
one  after  another  put  forth  (always  originating  in  peculiar  groups  of 
cells),  so  do  we  find  that  the  spiral  vessels,  woody  fibre,  &c.,  charac- 
teristic of  the  higher  organisms,  gradually  make  their  appearance. — Thus 
we  see  that  even  the  highest  Plants  have  to  pass  through  conditions 
closely  conformable  to  those  which  are  permanently  shown  in  the  lower ; 
and  that  the  parts  which  are  first  formed  are  destined  for  only  a  tem- 
porary purpose,  that  of  preparing  nourishment  for  the  evolution  of  more 
permanent  structures.  We  shall  find,  in  tracing  the  history  of  the  de- 
velopment of  the  higher  Animals,  that  exactly  the  same  general  fact 
may  be  observed,  in  even  a  more  striking  manner ;  the  number  of  difie- 
rent  stages  being  greater,  and  a  yet  larger  proportion  of  the  parts  first 
formed  having  a  merely  temporary  purpose,  and  being  destined  to  an 
early  decay,  as  soon  as  the  more  permanent  parts  of  the  fabric  shall 
have  been  evolved. 

782.  Among  many  of  the  lower  Animals,  a  multiplication  of  indivi- 
duals takes  place  by  a  process  that  closely  resembles  the  budding  of 
Plants ;  this  also  must  be  regarded,  not  as  a  proper  act  of  Generation, 
but  as  a  modification  of  the  ordinary  Nutritive  process.  The  same  may 
be  said  of  the  powers  of  reparation,  which  every  Animal  body  possesses 
in  a  greater  or  less  degree,  but  which  are  by  far  the  most  remarkable 
among  the  lower  tribes ;  for  when  an  entire  member  is  renewed  (as  in 
the  Star-fish),  or  even  the  whole  body  is  regenerated  from  a  small  frag- 
ment (which  is  the  case  in  many  Polypes),  it  is  by  a  process  exactly 
analogous  to  that  which  is  concerned  in  the  reparation  of  the  simplest 
wound  in  our  own  bodies,  and  which,  as  already  explained  (§  636),  is 
but  a  modification  of  the  process  that  is  constantly  renewing,  more  or 
less  rapidly,  every  portion  of  their  fabric.  Although  the  buds  thus 
produced  and  separated  are  usually  developed  into  the  likeness  of  the 
parent  stock,  yet  this  is  sometimes  not  the  case,  the  stock  possessing  one 
form,  and  the  bud  another,  which  may  be  quite  difi'erent ;  as  when  certain 
fixed  composite  Zoophytes  bud  off  free-moving  solitary  Medusae,  these 
last  depositing  ova,  from  which  the  Zoophytic  type  is  regenerated. 
When,  however,  this  phenomenon,  to  which  the  name  of  "  alterations 
of  generations"  has  been  given  (erroneously,  in  the  Author's  opinion),* 
is  carefully  examined,  it  is  found  that  the  bud  thus  detached  is  really 

*  For  a  discussion  of  this  subject,  see  the  Author's  ''Principles  of  General  and  Com- 
parative Physiology,"  chap,  xviii.,  sect.  1. 


440  OF  GENERATION  AND  DEVELOPMENT. 

the  generative  apparatus  of  the  parent  stock,  furnished  (it  may  be)  with 
nutrient  and  locomotive  organs  of  its  own ;  and  that  neither  can  be  re- 
garded as  a  complete  organism  without  the  other.  Thus,  the  Medusa 
contains  the  proper  generative  apparatus  of  the  Zoophyte,  which 
developes  no  other ;  and  the  "  aggregate"  Salpse  that  are  budded- 
forth  from  a  kind  of  stalk  in  the  interior  of  the  "  solitary"  form,  must 
be  regarded  as  altogether  constituting  its  true  generative  apparatus, 
since  it  never  produces  any  other.  In  all  instances  it  will  be  found, 
that  whatever  may  be  the  variations  which  present  themselves  in  the 
entire  history  of  any  species,  the  immediate  product  of  the  true  Gene- 
rative act  is  always  the  same. 

783.  This  act,  in  Animals  as  in  Plants,  requires  the  concurrent 
action  of  two  sets  of  organs,  evolving  "sperm-cells"  and  "germ-cells" 
respectively ;  and  it  is  curious  that  these  should  present  the  closest 
approach  to  those  of  the  higher  Cryptogamia,  rather  than  to  those  of 
Plants  above  or  below  them  in  the  scale.  The  two  sets  of  organs  may 
be  united  in  the  same  individual,  as  they  are  in  most  Plants ;  and  the 
ova  may  be  fertilized  from  the  seminal  cells  of  the  same  being ; — as 
happens  in  many  Zoophytes  and  in  some  of  the  lowest  tribes  of  Mol- 
lusca.  Or,  the  two  sets  of  organs  being  present  in  each  individual,  it 
may  not  be  capable  of  self-impregnation ;  but,  in  the  congress  of  two 
individuals,  each  impregnates,  and  is  impregnated  by,  the  other ; — as 
may  be  observed  in  the  Snail,  and  many  of  the  higher  Molluscs.  Or 
the  sexes  may  be  altogether  distinct ;  one  individual  possessing  only  the 
male  or  spermatic  organs ;  and  the  other  the  female,  or  germ-nourishing 
apparatus ; — this  is  observed  in  the  higher  classes  of  the  Radiated,  Mollus- 
cous, and  Articulated  sub-kingdoms ;  and  it  is  the  case  in  all  Vertebrata. 

784.  The  earliest  part  of  the  history  of  Embryonic  Development  is 
nearly  the  same  in  all  Animals ;  for  it  consists  in  the  multiplication  of 
the  single  cell  of  which  the  original  germ  is  composed,  until  a  cluster  is 
formed,  all  the  cells  of  which  appear  to  be  in  all  respects  similar  to  one 
another.  Each  of  these  cells  either  takes  into  itself,  or  draws  around 
it,  a  portion  of  the  vitellus  or  yolk,  which  is  the  nutrient  substance  of 
the  ovum  ;  and  thus  either  the  whole  of  this  vitellus,  or  a  portion  of  it, 
is  subdivided  into  a  number  of  minute  spherules,  altogether  constituting 
what  is  known  as  the  "mulberry  mass"  (Fig.  135).  The  former  seems 
to  be  the  case,  when  the  grade  of  development  of  the  organism  which  is 
to  be  formed  at  the  expense  of  the  yolk  is  very  low ;  whilst  the  latter 
plan  is  followed,  when  the  yolk  is  destined  to  afford  a  prolonged  suste- 
nance to  the  embryo,  which  attains  a  high  degree  of  development  whilst 
supported  upon  it  alone.  Thus  among  the  Invertebrata  generally,  we 
find  that  the  embryo  comes  forth  from  the  egg  in  a  very  simple  condi- 
tion, a  large  part  of  its  structure  having  undergone  but  little  change 
from  the  state  of  the  "mulberry  mass;"  and  in  these,  the  whole  yolk 
undergoes  subdivision.  The  same  is  the  case,  too,  in  the  Batrachian 
Reptiles,  which  issue  from  the  egg  in  a  form  very  different  from  that 
into  which  they  are  to  be  subsequently  developed ;  and  it  is  the  case 
even  with  Mammalia,  but  for  a  very  different  reason,  their  embryonic 
structure,  formed  at  the  expense  of  the  yolk,  being  destined  to  acquire 
additional  material  for  its  full  development  from  a  source  altogether 


SIMPLEST   FORMS   OF   GENERATIVE   PROCESS.  441 

different.  In  the  highest  Mollusca,  however,  as  also  in  Fishes,  Reptiles, 
and.  Birds,  the  portion  of  the  yolk  which  undergoes  subdivision  is  com- 
paratively small ;  and  the  great  mass  of  the  vitellus  is  destined  to  be 


Successive  stages  of  segmentation  in  the  vitellus  of  the  Ovum  of  Ascaris  acuminata : — A,  ovum  recently 
impregnated,  the  yolk-bag  slightly  separated  from  the  enveloping  membrane;  b,  first  fission  into  two 
halves;  c,  second  fission,  forming  four  segments;  D,  yolk,  now  divided  into  numerous  segments;  e,  formation 
of  "mulberry  mass"  by  further  segmentation;  F,  the  mass  of  cells  now  beginning  to  show  the  form  of  the 
future  worm;  g,  further  progress  of  its  evolution;  H,  the  worm,  formed  by  the  conversion  of  the  yolk-cells, 
now  nearly  mature. 

subsequently  absorbed  into  the  substance  of  the  germ,  by  a  process 
analogous  to  that  by  which  the  food  of  the  adult  is  imbibed.  Hence 
the  portion  of  their  yolk  which  undergoes  subdivision,  and  helps  to  con- 
stitute the  "mulberry  mass,"  may  be  termed  the  "germ-yolk,"  whilst 
the  remainder  may  be  designated  as  the  "food-yolk." 

785.  When  the  whole  of  the  yolk  is  taken  into  the  mulberry  mass, 
the  formation  of  the  embryo  is  usually  the  result  of  the  progressive 
metamorphosis  of  its  parts ;  the  cells  of  the  surface  being  converted  into 
the  integument,  and  those  of  the  inner  part  into  the  internal  organs. 
This  is  the  case,  for  example,  in  the  Intestinal  Worm,  some  of  the  stages 
in  whose  development  are  shown  in  Fig.  135.  The  embryonic  con- 
dition of  many  of  the  organs  is  frequently  retained,  at  the  time  when 
the  young  animal  comes  forth  from  the  egg ;  those  parts  only  being 
completed  which  are  necessary  to  enable  it  to  obtain  its  nutriment. 
Other  organs  are  subsequently  evolved,  at  the  expense  of  the  food  thus 
introduced  ;  and  thus  a  complete  change  or  metamorphosis  may  take 
place,  in  regard  alike  to  external  form  and  to  internal  structure,  between 
the  larval  and  adult  states.  Of  this  phenomenon  we  have  charac- 
teristic examples  in  the  groups  of  Insects  and  Batrachia  ;  and  although 
it  was  formerly  considered  exceptional,  it  is  now  known  to  be  the  or- 
dinary occurrence  among  the  lower  tribes  of  animals ;  it  being  com- 
paratively rare  for  any  of  them  to  come  forth  from  the  egg  under  their 
adult  forms.  This  change  is  sometimes  obviously  gradual,  as  in  the 
progressive  advance  of  the  Tadpole  into  the  condition  of  the  Frog ;  but 
it  is  sometimes  apparently  sudden,  as  when  the  Chrysalis  skin  is  thrown 
off,  and  the  perfect  Insect  comes  forth.  In  the  latter  case,  however, 
the  change  is  really  just  as  gradual  as  in  the  former ;  since  the  develop- 
ment of  the  organs  characteristic  of  the  perfect  Insect  is  taking  place 
during  the  whole  of  the  Chrysalis  period,  to  be  displayed  and  brought 


442  OF  GENERATION  AND  DEVELOPMENT. 

into  use  at  its  termination.  Thus  the  whole  life  of  the  Insect,  up  to  its 
last  change,  may  be  regarded  as  one  of  prolonged  embryonic  develop- 
ment ;  and  the  same  may  be  said  of  that  of  the  Frog,  up  to  the  time 
when  its  permanent  organs  are  fully  evolved. — No  such  ostensible  me- 
tamorphosis takes  place,  however,  in  any  of  the  animals  which  are  pro- 
vided with  a  "food-yolk;"  for  this  supplies  that  material  for  the  con- 
tinued development  of  the  embryo  within  the  egg,  which  is  elsewhere 
to  be  obtained  out  of  it ;  and  thus  the  embryo  is  supported,  until  it  has 
nearly  attained  its  adult  condition,  although  far  from  having  acquired 
its  adult  size.  Now  in  all  these  cases,  it  is  very  interesting  to  remark 
that  the  first  nisus  is  towards  an  extension  of  the  embryonic  mass  as  a 
membranous  expansion  (evidently  analogous  to  the  cotyledon  of  the 
Flowering  Plants,  §  Y81)  over  the  "  food-yolk ;"  in  this  "  germinal  mem- 
brane," which  forms  a  sort  of  temporary  stomach,  blood-vessels  are  de- 
veloped, which  absorb  the  prepared  nutriment  and  convey  it  to  the  per- 
manent portion  of  the  embryonic  structure ;  and  when  its  function  is 
completed,  the  store  of  aliment  being  exhausted,  and  the  proper  nutrient 
apparatus  of  the  embryo  being  ready  for  action,  we  lose  sight  of  it  al- 
together. We  shall  find  that  a  similar  germinal  membrane  is  formed  in 
the  Human  ovum,  although  there  is  no  "  food-yolk ;"  its  formation  being 
apparently  requisite  for  ulterior  purposes,  and  the  portion  of  the  mul- 
berry mass  which  gives  origin  to  the  permanent  part  of  the  embryonic 
structure  being  comparatively  small. 

2.  Action  of  the  Male. 

Y86.  The  share  in  the  Reproductive  Function,  which  belongs  to  the 
Male  Sex,  essentially  consists  in  the  formation  and  liberation  of  the 
fertilizing  bodies  termed  Spermatozoa.  These  are  prepared  within 
peculiar  cells,  as  already  described  (§  241);  and  the  "sperm  cells"  are 
either  scattered  through  the  soft  parenchyma  of  the  body,  as  happens 
among  some  of  the  lowest  anim'als  ;  or  they  are  confined  to  certain  parts 
of  it,  as  in  those  a  little  more  elevated  in  the  scale ;  or  they  are  formed 
within  follicles  or  tubes,  clustered  together  into  an  organ  of  a  glandular 
character,  known  as  the  Testis.  Such  an  organ  is  found  in  all  Insects 
and  Mollusca ;  as  well  as  in  Vertebrated  Animals.  In  the  first  of  these 
classes,  it  is  formed  on  the  general  plan  of  their  proper  glands  (§  720) ; 
being  usually  composed  of  tubes,  more  or  less  elongated,  and  some- 
times terminating  in  enlarged  follicles.  In  the  Molluscs,  on  the  other 
hand,  it  is  almost  invariably  composed  of  clusters  of  follicles.  In  either 
case,  the  seminal  cells  are  developed  within  the  tubes  or  follicles,  as 
are  the  ordinary  secreting  cells  of  the  Liver  or  Kidney  within  the 
tubes  or  follicles  of  those  glands ;  and  their  contents  are  discharged  by 
an  excretory  duct,  which  terminates  in  an  organ  that  conveys  them  out 
of  the  body,  either  emitting  them  into  the  surrounding  water  (as  hap- 
pens with  many  Mollusca),  or  depositing  them  within  the  body  of  the 
female.  It  is  curious  that,  in  some  of  the  lowest  Fishes,  we  should 
return  to  one  of  the  simplest  conditions  of  this  organ, — a  mass  of 
vesicles,  without  any  excretory  duct.  In  these  cases  the  secretion 
formed  within  the  vesicles  escapes,  by  their  rupture,  into  the  abdominal 


I 


ACTION   OF  THE   MALE. 


443 


Fig.  136. 


cavity ;  whence  it  passes  out  by  openings  that  lead  directly  to  the  ex- 
terior.— The  Testis  in  Man  is  formed,  in  every  essential  particular,  upon 
the  plan  of  the  ordinary  Glands.  It  consists  of  several  distinct  lobules^ 
separated  by  processes  of  the  fibrous  envelope,  or 
tunica  albuginea,  which  pass  down  between  them ; 
and  each  lobule  consists  of  a  mass  of  convoluted 
tubuli  seminiferi,  through  which  blood-vessels  are 
minutely  distributed.  The  diameter  of  these  tubuli 
is  tolerably  uniform ;  being,  when  they  are  not 
over-distended,  from  l-195th  to  1-lTOth  of  an  inch. 
They  form  frequent  anastomoses  with  each  other ; 
and  on  this  account  it  is  difficult  to  trace  out  their 
free  or  caecal  extremities.  The  tubuli  of  each  testis 
discharge  their  contents  into  an  efferent  duct,  the 
Vas  deferens ;  and  by  this  the  product  is  conveyed 
into  the  Vesiculi  seminalis  on  each  side,  which,  like 
the  gall-bladder  and  urinary  bladder,  serves  to  store 
up  the  secretion  until  the  proper  time  arrives  for 
discharging  it.  The  product  of  the  action  of  the 
Testis  consists  of  a  fluid,  through  which  the  Sper- 
matozoa are  diffused  ;  these  last  bodies  being  usually 
set  free  by  the  rupture  of  the  seminal  cells,  before 

they  leave  the  tubuli  of  the  testis.       It  is  difficult  to        Anatomy  of  the  Testis : 

determine  the  precise  characters  of  the  fluid  portion  \  \'  Th^e^Je'Si^tinum  tSl 
of  the  secretion ;  as  this  is  mingled  with  other  se-  3,'  s'  The  lobuu  testis.  4, 4. 
cretions  (such  as  that  of  the  Prostate  gland,  and  of  testis'TThe  vasaeCFerentia, 
the  mucous  lining  of  the  Vesiculse  seminales  and  L'nled'^n'thir'diag^am!'''?: 
spermatic  ducts,)  before  it  is  emitted.  And  an  SnJ  ?S?gIoTufrSjoTof4" 
exact  analysis  is  not  of  much  consequence :  since  epididymis,    s.  The  body  of 

,1  •Z'  1       r  ^     .  1      i      .  1  V  /»   the  epididymis.  9.  The  globus 

there  can  be  no  doubt  that  the  peculiar  powers  oi  minor  of  the  epididymis,  lo. 
the  fluid  depend  upon  the  Spermatozoa.  It  may  vas'curm  atJrans.  ^^'  ^^' 
be  stated,  however,  that  the  Spermatic  fluid  has 
an  alkaline  reaction,  and  that  it  contains  albumen,  together  with  a 
peculiar  animal  principle  termed  Spermatine ;  and  that  it  also  includes 
saline  matter,  consisting  chiefly  of  the  muriates  and  phosphates,  espe- 
cially the  latter,  which  form  crystals  when  the  fluid  has  stood  for  some 
little  time. 

787.  The  Spermatozoa^  or  minute  filamentous  todies  set  free  by  the 
rupture  of  the  spermatic  cells,  are  distinguished  by  their  power  of 
spontaneous  movement,  which  occasioned  them  to  be  long  regarded  as 
proper  Animalcules.  It  is  now  clear,  however,  from  the  history  of  their 
development,  as  well  as  from  other  considerations,  that  they  cannot  be 
justly  regarded  in  this  light ;  and  that  they  are  analogous  to  the  repro- 
ductive particles  of  Plants,  which,  in  many  cases,  exhibit  a  spontaneous 
motion  of  extraordinary  activity,  after  they  have  been  set  free  from  the 
parent  structure.  The  Human  Spermatozoon  consists  of  a  little  oval 
flattened  "boiiy,"  from  the  l-600th  to  the  l-800th  of  a  line  in  length ; 
from  which  proceeds  a  filiform  "  tail,"  gradually  tapering  to  a  very  fine 
point,  of  l-50th  or  at  most  l-40th  of  a  line  in  length.  The  whole  is 
perfectly  transparent ;  and  nothing  that  can  be  called  structure  can  be 


444  OF  GENERATION  AND  DEVELOPMENT. 

satisfactorily  distinguished  within  it.  The  movements  are  principally 
excited  by  the  undulations  of  the  tail,  which  give  a  propulsive  action 
to  the  body.  They  may  continue  for  many  hours  after  the  emission  of 
the  fluid ;  and  they  are  not  checked  by  its  admixture  with  other  secre- 
tions, such  as  the  urine,  and  the  prostatic  fluid.  When  the  seminal 
fluid  remains  in  contact  with  a  living  surface  (as  when  deposited  in  the 
generative  organs  of  the  female),  the  Spermatozoa  may  retain  their 
vitality  for  some  days ;  and  an  instance  has  already  been  referred  to 
(§  240),  in  which  the  later  stages  of  the  development  of  the  Sperma- 
tozoa actually  take  place  in  this  situation, — the  seminal  fluid  emitted 
by  the  male  (among  many  Crustacea)  not  containing  any  Spermatozoa 
completely  formed,  but  numerous  spermatic  cells,  which  undergo  the 
remainder  of  their  development,  and  then  rupture  and  set  free  their 
contents,  within  the  oviducts  of  the  female. 

788.  The  power  of  procreation  does  not  exist  in  the  Human  Male 
(except  in  rare  ckses)  until  the  age  of  from  14  to  16  years  ;  at  which 
epoch,  the  sexual  organs  undergo  a  much-increased  development ;  and 
the  instinctive  desire,  which  leads  to  the  use  of  them,  is  awakened  in 
the  mind.  From  that  time  to  an  advanced  age,  the  procreative  power 
remains,  in  the  healthy  state  of  the  system  ;  unless  it  be  exhausted  by 
excessive  use  of  it,  or  by  too  energetic  a  direction  of  the  mental  or 
corporeal  powers  to  some  other  object.  The  formation  of  Seminal  fluid 
being,  like  the  proper  acts  of  Secretion,  very  much  influenced  by  con- 
ditions of  the  Nervous  System,  is  increased  by  the  continual  direction 
of  the  mind  towards  objects  which  arouse  the  sexual  propensity ;  and 
thus,  if  sexual  intercourse  be  very  frequent,  a  much  larger  quantity  of 
the  fluid  will  be  produced,  than  if  it  is  more  rarely  emitted,  although 
the  amount  discharged  on  each  occasion  will  be  less.  The  formation 
of  this  product  is  evidently  a  great  tax  upon  the  corporeal  powers  ;  and 
it  is  a  well-known  fact,  that  the  highest  degree  of  bodily  and  mental 
vigour  is  inconsistent  with  more  than  a  very  moderate  indulgence  in 
sexual  intercourse ;  whilst  nothing  is  more  certain  to  reduce  the  powers, 
both  of  body  and  mind,  than  excess  in  this  respect. 

789.  It  may  be  stated  as  a  general  law,  prevailing  equally  in  the 
Vegetable  and  Animal  kingdoms, — that  the  development  of  the  indi- 
vidual, and  the  reproduction  of  the  species,  stand  in  an  inverse  ratio 
to  each  other.  We  have  seen  that,  in  many  organized  beings,  the 
death  of  the  parent  is  necessary  to  the  production  of  a  new  generation ; 
and  even  in  numerous  species  of  Insects  it  follows  very  speedily  upon 
the  sexual  intercourse.  It  is  a  curious  fact,  that  Insects  which  usually 
die,  the  male  almost  immediately  after  the  act  of  copulation,  and  the 
female  very  soon  after  the  deposition  of  the  eggs,  may  be  kept  alive 
for  many  weeks  or  even  months,  by  simply  preventing  the  copulation. 
And  there  can  be  no  doubt  that,  in  the  Human  race,  early  death  is  by 
no  means  an  unfrequent  result  of  the  excessive  or  premature  employ- 
ment of  the  genital  organs ;  and  where  this  does  not  produce  an 
immediately-fatal  result,  it  lays  the  foundation  of  future  debility,  that 
contributes  to  produce  any  forms  of  disease  to  which  there  may  be  a 
constitutional  predisposition,  especially  those  of  a  Scrofulous  nature. 

790.  The  emission  of  the  Spermatic  fluid  is  an  act  of  a  purely  reflex 


ACTION   OF   THE   FEMALE.  445 

nature  ;  the  Will  having  no  power  either  to  effect  or  to  restrain  it. 
The  stimulus  is  given  by  the  friction  of  the  surface  of  the  Glans  Penis 
against  the  rugous  walls  of  the  Vagina ;  the  sensibility  of  the  organ 
being  at  the  same  time  much  increased,  by  the  determination  of  blood 
to  it.  The  impression  is  at  last  sufficiently  strong  to  produce,  through 
the  medium  of  the  lower  part  of  the  Spinal  cord  (which  is  the  gangli- 
onic centre  of  the  circle  of  afferent  and  efferent  nerves  connected  with 
this  organ),  a  reflex  contraction  of  the  muscles  surrounding  the  Yesi- 
culse  seminales.  These  receptacles  discharge  their  contents  (which 
consist  partly  of  the  Spermatic  fluid,  and  partly  of  a  secretion  of  their 
own)  into  the  Urethra;  and  from  this  they  are  expelled,  with  some 
degree  of  force,  and  with  a  kind  of  spasmodic  action,  by  its  own  Com- 
pressor muscles.  Although  the  sensations  concerned  in  this  act  are 
ordinarily  most  acutely  pleasurable,  yet  there  appears  to  be  sufficient 
evidence  that  they  are  by  no  means  essential  to  its  performance  ;  and 
that  the  impression  conveyed  to  the  Spinal  cord  may  excite  the  con- 
traction of  the  Ejaculator  muscles,  like  other  reflex  operations,  without 
producing  sensation  (§  394). 

3.  Action  of  the  Female. 

T91.  The  share  of  the  Female  in  the  Generative  act  is  greater  than 
that  of  the  Male;  for  she  not  only  furnishes,  in  the  "germ-cell,"  a 
product  which  is  as  essential  as  that  supplied  by  the  "  sperm-cell"  for 
the  first  formation  of  the  germ ;  but  she  also  supplies  it  with  the  mate- 
rials which  it  requires  for  its  development,  up  to  the  condition  in  which 
it  can  support  its  own  life.  The  mode  in  which  this  is  accomplished, 
is  essentially  the  same  with  that  in  which  the  process  is  effected  in 
Plants.  In  certain  parts  of  the  female  structure  are  developed  pecu- 
liar bodies  termed  ova  ;  which  contain,  not  merely  the  germ-cells,  but  in 
addition  a  store  of  nutriment  adapted  to  supply  the  wants  of  the  germ. 
The  fertilizing  influence  finds  its  way  into  these  ;  and  the  germs  thus 
produced  begin  to  grow  at  the  expense  of  the  material  with  which  they 
are  surrounded.  This,  as  already  pointed  out,  may  enable  the  embryo 
to  develope  itself,  without  any  further  assistance  (save  a  warm  tempe- 
raturo)  into  the  form  it  is  permanently  to  assume  ;  as  in  the  case  of 
Birds  and  Reptiles,  which  do  not  come  forth  from  the  investments  of 
the  egg,  until  they  have  attained  the  form  characteristic  of  the  group 
to  which  they  belong.  Or  it  may  only  serve  for  the  early  part  of  the 
process  ;  and  one  of  two  methods  may  then  be  employed  to  complete 
it; — either  a  new  connexion  is  formed  between  the  parent  and  the 
embryo,  by  which  the  former  continues  to  supply  the  latter  with  nutri- 
ment, more  directly  from  its  blood, — as  is  the  case  with  Mammalia, — or 
the  embryo  issues  from  the  egg,  in  a  condition  very  unlike  that  which 
it  is  permanently  to  attain,  but  in  a  form  which  enables  it  to  acquire  its 
own  nourishment,  and  to  pass  through  the  latter  stages  of  its  evolution 
quite  independently  of  any  assistance  from  its  parent :  this  is  the  case 
with  a  large  proportion  of  the  Invertebrata. 

792.  The  Ova,  like  the  seminal  cells,  are  scattered  through  the  soft 
parenchyma  of  the  body,  in  animals  of  the  lowest  class ;  but  they  are 


446  OF  GENERATION  AND  DEVELOPMENT. 

more  commonly  developed  in  certain  distinct  portions  of  the  fabric; 
being  sometimes  formed  in  the  midst  of  solid  masses  of  areolar  or  cel- 
lular texture  ;  whilst  in  other  instances  they  are  developed,  like  the 
spermatic  cells,  in  the  interior  of  tubes  and  vesicles  resembling  those 
of  glands,  and  furnished  with  an  excretory  duct.  The  latter  condition 
obtains  in  the  greater  proportion  of  the  higher  Invertebrated  animals, 
and  in  some  Fishes ;  but  in  the  Vertebrated  classes  we  return  to  the 
type  which  characterizes  the  egg-producing  organs  in  many  Zoophytes, 
— namely,  the  development  of  the  egg  in  the  midst  of  a  mass  of  solid 
parenchyma,  from  which  it  gradually  makes  its  way,  to  escape  into  the 
visceral  cavity.  The  Ovarium  of  the  Mammal,  Bird,  or  Reptile,  as  well 
as  that  of  most  Fishes,  differs  entirely,  therefore,  from  that  of  the  In- 
vertebrata;  for  the  latter  have  all  the  essential  characters  of  true 
glands  ;  whilst  the  former  are  nothing  else  than  masses  of  parenchyma, 
copiously  supplied  with  blood-vessels,  and  having  dispersed  through 
their  substance  certain  peculiar  cells,  termed  ovisacs,  within  which  the 
ova  are  developed.  In  order  that  the  latter  may  be  set  free,  not  only 
must  the  ovisac  itself  burst  (like  parent-cells  in  general),  but  the  pecu- 
liar tissue  and  the  envelopes  of  the  ovarium  must  likewise  give  way. 
When  the  ova  thus  escape  into  the  abdominal  cavity,  they  may  lie  there 
for  some  time,  at  last  to  be  discharged  through  simple  openings  in  its 
walls,  as  happens  in  those  Fishes  which  have  this  form  of  ovarium  ;  or 
they  may  be  at  once  received  into  the  trumpet-shaped  expansion  of 
tubes,  that  shall  convey  them  to  these  orifices.  These  tubes  are  termed 
oviducts,  in  common  with  the  excretory  ducts  of  the  glandular  ovaria 
of  Invertebrated  animals ;  for  their  function  is  the  same, — that  of  con- 
veying the  ova  to  the  outlet  by  which  they  are  extruded  from  the  body. 

Fig.  137. 


The  Uterus  with  its  appendages  riewed  on  their  anterior  aspect.  1.  The  hody  of  the  uterus.  2.  Its  fundus. 
3.  Its  cervix.  4.  The  os  uteri.  6.  The  vagina;  the  number  is  placed  on  the  posterior  raph6  or  columna, 
from  which  the  transverse  rugae  are  seen  passing  off  at  each  side.  6,  6.  The  broad  ligament  of  the  uterus. 
7.  A  convexity  of  the  broad  ligament  formed  by  the  ovary.  8,  8.  The  round  ligaments  of  the  uterus.  9,  9. 
The  Fallopian  tubes.  10, 10.  The  fimbriated  extremities  of  the  Fallopian  tubes;  on  the  left  side  the  mouth 
of  the  tube  is  turned  forwards  in  order  to  show  its  ostium  abdominale.  11.  The  ovary.  12.  The  utero-ova- 
rian  ligament.  13.  The  Fallopio-ovarian  ligament,  upon  which  some  small  fimbriae  are  continued  for  a  short 
distance.  14.  The  peritoneum  of  the  anterior  surface  of  the  uterus.  This  membrane  is  removed  on  the  left 
side,  but  on  the  right  is  continuous  with  the  anterior  layer  of  the  broad  ligament. 

They  are  represented  in  Mammalia  by  the  Fallopian  tubes,  which  are 
true  oviducts,  although  they  terminate  in  the  uterus  instead  of  proceed- 
ing directly  to  the  outlet.  And  it  is  by  the  fimbriated  extremities  of 
the  Fallopian  tubes  (Fig.  13T,  10,  10),  which  apply  themselves  closely 


STRUCTURE   AND   DEVELOPMENT   OF   THE   OVUM.  447 

to  the  surface  of  the  ovaries  at  the  time  of  the  discharge  of  the  ova, 
that  these  are  received  and  conveyed  to  the  uterus,  instead  of  being 
allowed  (as  in  some  of  the  lower  animals)  to  fall  into  the  abdominal 
cavity. 

793.  There  are  many  cases  among  the  lower  classes,  in  which  the 
ovum  is  retained  within  the  oviducts,  so  that  the  young  conies  into  the 
world. alive ;  and  there  are  a  few  in  which,  during  this  delay,  it  receives 
a  direct  supply  of  additional  nourishment  from  the  fluids  of  its  parent. 
It  is  in  the  Mammalia,  however,  that  we  find  the  mosf  remarkable  and 
complete  provision  for  this  purpose.  Still,  the  lowest  division  of  this 
group  approximates  closely,  in  the  type  of  its  generative  apparatus,  to 
the  Oviparous  Yertebrata;  for  the  oviducts  of  the  Monotremata  remain 
distinct  from  each  other,  and  terminate  separately  in  the  uro-genital 
canal,  each  of  them  having  first  undergone  dilatation  into  a  uterine 
cavity,  so  that  these  animals  have  two  completely  distinct  uteri.  In 
the  Marsupialia,  there  is  a  closer  approximation  of  the  two  lateral  sets 
of  organs  on  the  median  line ;  for  the  oviducts  converge  towards  one 
another,  and  meet  on  the  median  line,  but  without  coalescing ;  so  that 
these  animals  have  a  true  "  double  uterus,"  opening  by  two  orifices  into 
the  vaginal  canal, — a  condition  which  is  sometimes  met  with  as  a  malfor- 
mation in  the  Human  female.  The  vaginal  canal,  however,  is  also 
double ;  which  is  less  frequently  observed  in  the  Human  species.  The 
two  preceding  orders  constitute  the  sub-class  of  hnplaeental  Mammals ; 
the  development  of  theit-  ova  within  the  uteri  being  cut  short  at  a  period 
anterior  to  the  formation  of  the  placenta  (§  818). — As  we  ascend 
through  the  series  of  Placental  Mammals,  we  find  the  lateral  coales- 
cence of  the  uterine  dilatations  of  the  Fallopian  tubes  becoming  more 
and  more  complete.  It  first  shows  itself  in  the  vagina,  which  is  every- 
where single,  although  a  trace  of  separation  into  two  lateral  halves  is 
seen  in  the  Mare,  Ass,  Cow,  Pig,  and  Sloth,  in  which  animals  it  is  tra- 
versed, in  the  virgin  state,  by  a  narrow  vertical  partition.  In  many  of 
the  Rodentia,  the  uterus  still  remains  completely  divided  into  two 
lateral  halves,  opening  into  the  vagina  by  separate  orifices ;  whilst  in 
others,  these  coalesce  at  their  lower  portion,  forming  a  rudiment  of  the 
true  "body"  of  the  uterus  of  the  Human  female.  This  part  increases 
in  the ,  more  elevated  Herbivora  and  Carnivora,  at  the  expense  of  the 
lateral  ununited  portions,  which  are  now  termed  the  "  cornua ;"  but 
even  in  the  lower  Quadrumana,  the  uterus  is  someWhat  cleft  at  its  sum- 
mit, and  the  "angles,"  into  which  the  oviducts  enter,  form  a  consider- 
able part  of  the  whole  organ.  As  we  ascend  through  the  Quadruma- 
nous  series  towards  Man,  we  find  the  "body"  of  the  uterus  increasing, 
and  the  "angles"  diminishing  in  proportion,  until  the  original  division 
is  completely  lost  sight  of,  except  in  the  slight  dilatation  of  the  cavity 
at  the  points  at  which  the  Fallopian  tubes  enter  it. 

794.  Having  thus  briefly  noticed  the  most  important  characters  of 
the  organs  provided  for  the  original  production  and  for  the  subsequent 
reception  of  the  ova,  we  have  now  to  inquire  into  the  history  of  their 
development. — The  essential  structure  of  the  ovule,  or  unfertilized  Qgg^ 
appears  to  be  the  same  in  all  animals.  It  consists  externally  of  a 
membranous  sac,  termed,  from  the  nature  of  its  contents,  the  vitelline 


448  OF  GENERATION  AND  DEVELOPMENT. 

memhrane,  or  yolk-bag.  The  vitellus,  or  yolk,  consists  chiefly  of  albu- 
men and  oil-globules ;  and  floating  in  this  fluid  is  seen  a  cell  of  peculiar 
aspect,  termed  the  germinal  vesicle,  upon  the  wall  of  which  is  a  very 
distinct  nucleus,  termed  the  germinal  spot. — The  layer  of  albumen  sur- 
rounding the  yolk,  and  termed  the  white  of  the  Bird's  egg,  together 
with  the  membrane  which  envelopes  this  and  forms  the  basis  of  the 
shell,  are  not  added  until  after  the  ovum  has  left  the  ovarium.  They 
are  not  present  in  the  eggs  of  many  of  the  lower  Invertebrata ;  these 
consisting  merely  of  the  parts  which  are  formed  within  the  ovarium. 

795.  The  structure  of  the  ovule  in  Mammals  differs  in  no  essential 
particular  from  that  just  described;  but  the  yolk  is  much  less  in 
amount,  than  in  the  ovules  of  Invertebrated  animals ;  since  only  the 
very  earliest  stages  of  the  development  of  the  embryo  are  to  take  place 
at  its  expense.  The  vitelline  membrane  is  of  peculiar  thickness  and 
transparency ;  and  as,  when  the  ovum  is  compressed  under  the  micro- 
scope, it  is  seen  as  a  broad  transparent  belt,  it  is  commonly  known  as 
the  zona  pellucida.  We  shall  find  that  the  ovule,  after  leaving  the 
ovarium  and  receiving  the  fertilizing  influence,  becomes  enclosed,  whilst 
passing  through  the  Fallopian  tube,  with  a  layer  of  albuminous  matter, 
which  represents  the  white  of  the  Bird's  egg ;  and  with  an  additional 
fibrous  envelope,  which  corresponds  with  the  membrane  enveloping  the 
latter.  This  fibrous  membrane,  termed  the  Chorion,  afterwards  becomes 
subservient,  however,  to  various  important  changes ;  by  means  of  which 
the  ovum  is  again  brought  into  connexion  with  the  parent,  to  derive 
from  the  blood  of  the  latter  the  materials  requisite  for  the  continued 
development  of  the  embryo.  These  changes  will  be  described  hereafter 
(§§811,818). 

796.  The  Ovisac  of  Mammalia  forms  the  inner  layer  of  what  is 
termed  the  Giraafian  follicle,  after  the  name  of  its  discoverer ;  and  in- 
stead of  closely  enveloping  the  ovulum,  as  it  does  in  oviparous  animals, 
it  contains  in  addition  to  it,  a  quantity  of  granular  matter,  consisting 
of  cells  arranged  in  membranous  layers,  together  with  fluid.  In  the 
immature  ovisac,  these  cells  occupy  nearly  the  whole  space  between  the 
ovisac  and  the  ovum,  but  they  gradually  dissolve  away,  especially  on 
the  side  nearest  the  surface  of  the  ovary ;  and  at  the  same  time  an  al- 
buminous fluid  is  effused  from  the  deeper  part  of  the  ovisac,  which 
pushes  before  it  the  residual  layer  of  cells  that  immediately  sur- 
rounds the  ovum  (forming  the  discus  proligerus),  and  thus  carries  it 
against  the  opposite  wall.  The  outer  layer  of  the  Graafian  follicle  is 
formed  by  a  thickening  and  condensation  of  the  surrounding  paren- 
chyma of  the  ovarium ;  and  it  is  quite  distinct  from  the  ovisac  which  it 
envelopes.  It  is  extremely  vascular,  and  is  evidently  destined  to 
afford  to  the  contained  structures  the  materials  for  their  development, 
which  they  receive  and  appropriate  by  their  own  powers  of  absorption 
and  assimilation. 

797.  The  Mammalian  Ovarium  may  be  seen,  even  in  the  foetal  ani- 
mal, to  contain  immature  ova,  enclosed  within  their  ovisacs ;  and  the 
several  parts  of  the  former  may  be  clearly  distinguished  in  those  which 
are  in  the  more  advanced  stages  of  development.  It  appears  that, 
during  the  period  of  childhood,  there  is  a  continual  rupture  of  the  ovi- 


I 


MENSTRUAL   DISCHARGE.  449 


sacs  (or  parent-cells),  and  a  discharge  of  ova,  at  the  surface  of  the  ova- 
rium ;  but  these  ova  never  attain  so  high  a  degree  of  development,  as  to 
ender  them  fit  for  impregnation.     Their  evolution  takes  place  more 
ompletelj,   as  well  as  more  rapidly,  at  the  period  of  puberty,  when 
there   is    a   greatly-increased  determination  of  blood   to   the   genital 
organs,  and  a  correspondingly-augmented  energy  in  their  nutritive  opera- 
tions.    At  this  epoch,  the  parenchyma  of  the  ovarium  is  crowded  with 
ovisacs ;  which  are  still  so  minute,  that  in  the  Ox,  according  to  Dr. 
Barry's  computation,  a  cubic  inch  would  contain  200  millions  of  them, 
ome  of  those  nearest  the  surface,  however,  are  continually  attaining 
creased  development ;  and  a  rupture  of  some  of  the  Graafian  follicles, 
nd  a  discharge  of  ova  prepared  for  impregnation,  from  the  exterior  of 
he  ovarium,  thenceforth  take  place,  with  more  or  less  tendency  to 
eriodicity,  during  the  whole  time  that  the  female  is  in  a  state  of  apti- 
ude  for  procreation. 

798.  In  the  Human  female,  the  period  of  Puberty  usually  occurs  be- 
een  the  13th  and  16th  years.    The  difi'erences  in  the  time  of  its  advent 

artly  depend  upon  individual  constitution,  and  partly  upon  various  ex- 
ernal  circumstances,  such  as  temperature,  habits  of  life,  &c.  As  a 
general  rule,  habitual  exposure  to  a  warm  atmosphere,  an  inert  life, 
sensual  indulgence,  and  circumstances  that  excite  the  sexual  feelings, 
favour  the  approach  of  Puberty ;  whilst  a  cold  climate  and  hardy  life 
retard  it.  The  appearance  of  the  Catamenial  discharge  usually  takes 
place  whilst  the  evolution  of  the  genital  organs  is  in  progress  ;  and  it  is  a 
decided  indication,  when  it  occurs,  that  the  aptitude  for  procreation  has 
been  attained.^  It  is  not  unfrequently  delayed  much  longer,  however ;  and 
its  absence. is  by  no  means  to  be  regarded  as  a  proof  of  inability  to  con- 
ceive. The  Catamenial  fluid,  as  it  proceeds  from  the  lining  membrane 
of  the  Uterus,  seems  to  be  nothing  else  than  Blood ;  but  in  its  passage 
through  the  vagina,  this  is  deprived  of  its  coagulating  power  by  admix- 
ture with  the  vaginal  mucus.  The  appearance  of  clots  in  the  discharge 
may  usually  be  regarded  as  an  indication  that  an  excess  of  blood  is 
escaping  from  the  uterine  surface.  In  some  cases  of  diflficult  Menstrua- 
tion, which  seem  to  depend  upon  a  state  of  low  inflammation  in  the 
Uterus,  the  fibrine  has  such  a  tendency  to  become  organized,  as  to  form 
shreds,  or  layers  of  false  membrane,  which  sometimes  plug  up  the  os 
uteri.  The  healthy  Menstrual  secretion  is  remarkable  for  its  very  acid 
character. — It  has  been  recently  maintained  that  this  periodical  dis- 
charge of  blood  from  the  lining  membrane  of  the  uterus  is  dependent 
upon  the  ovarian  oestrum;  but  there  seems  adequate  reason  for  the 
belief,  that,  although  the  two  phenomena  are  usually  consentaneous, 
yet  that  they  are  essentially  independent;  since  each  occasionally 
recurs  without  being  accompanied  by  the  other.  The  catamenial  dis- 
charge usually  makes  its  appearance  pretty  regularly  (save  during  preg- 
nancy and  lactation)  at  intervals  of  28  days ;  but  there  are  many  females 
in  whom  its  recurrence  takes  place  with  no  less  regularity  at  shorter  or 
at  longer  intervals.  The  duration  of  the  flow,  too,  is  subject  to  great 
variations ;  for  in  some  individuals  it  does  not  last  above  a  day  or  two, 
whilst  in  others  it  continues  a  week  or  more. 

799.  This  flux  of  blood  from  the  lining  membrane  of  the  Uterus  is 


450  OP  GENERATION  AND  DEVELOPMENT. 

not  confined  to  the  Human  female,  as  was  formerly  supposed;  but 
occurs  in  some  of  the  lower  Mammalia  in  the  state  of  heat^  or  periodi- 
cal aptitude  for  procreation,  at  which  time  the  ovarium  contains  ova 
ready  for  impregnation.  The  chief  peculiarity  attending  its  appearance 
in  the  Human  female,  is  its  regular  monthly  return.  In  the  natural 
condition  of  many  of  the  lower  Mammalia,  as  in  Oviparous  animals, 
the  period  of  heat  recurs  at  some  one  time  of  the  year, — usually  in 
the  spring ;  or,  in  the  smaller  and  more  prolific  species,  from  two  to 
six  times.  And  in  those  which  have  undergone  a  change  by  domesti- 
cation, the  recurrence  is  usually  irregular,  depending  upon  various 
circumstances  of  regimen,  temperature,  &c.  The  general  analogy 
between  the  Menstruation  of  the  Human  female  and  the  Heat  of  the 
lower  Mammalia, — consisting  in  the  peculiar  aptitude  for  impregnation 
which  then  exists  in  consequence  of  the  maturation  of  ova  in  the  ovarium, 
— cannot  now  be  questioned ;  but  it  appears  that  in  the  Human  female 
ova  may  be  matured  and  impregnated  at  any  part  of  the  period  which 
elapses  between  the  occurrences  of  the  Catamenial  discharge ;  though 
it  is  certain  that  the  aptitude  for  conception  is  much  greater,  during 
the  few  days  which  precede  and  follow  the  menstrual  period,  than  at 
any  intervening  time.  The  duration  of  the  period  of  aptitude  for  pro- 
creation, which  is  marked  by  the  continued  appearance  of  the  Cata- 
menia,  is  more  limited  in  Women  than  in  Men ;  usually  terminating  at 
about  the  45th  year.  It  is  sometimes  prolonged,  however,  for  ten  or 
even  fifteen  years  longer ;  but  cases  are  rare,  in  which  women  above  50 
years  of  age  have  borne  children.  There  is  usually  no  menstrual  flow 
during  pregnancy  and  lactation ;  in  fact  the  cessation  of  the  Cata- 
menia  is  usually  one  of  the  first  signs  indicating  that  conception  has 
taken  place.  It  is  by  no  means  uncommon,  however,  for  them  to 
appear  once  or  twice  subsequently  to  Conception ;  and  their  appearance 
during  Lactation,  especially  if  it  be  much  prolonged,  is  still  more  fre- 
quent ;  hence  it  might  be  inferred,  that  the  continuance  of  Lactation 
may  not  prevent  a  fresh  conception, — which  is  found  to  be  true  in 
practice. 

800.  We  shall  now  take  a  brief  survey  of  the  changes  which  occur 
in  the  Ovulum,  when  it  is  being  prepared  for  fecundation ;  and  of  the 
principal  features  of  its  subsequent  development.— Up  to  the  period 
when  the  Ovule  is  nearly  brought  to  maturity,  it  remains  suspended 
in  the  centre  of  the  cavity  of  the  Ovisac ;  but  it  then  begins  to  move 
towards  that  side  of  the  Graafian  follicle,  which  is  nearest  the  surface 
of  the  ovarium.  An  important  change  is  at  the  same  time  occurring 
in  the  Graafian  follicle  itself ;  for  whilst  the  part  with  which  the  ovule 
comes  in  contact  gradually  thins  away,  the  outer  or  vascular  layer  of 
the  remainder,  especially  on  that  side  most  deeply  imbedded  in  the 
ovary,  becomes  much  increased  in  thickness ;  and  a  great  increase 
takes  place  at  that  part,  in  the  cellular  layer  that  lines  the  ovisac, 
which  presents  a  reddish  glutinous  aspect.  This  subsequently  under- 
goes a  still  greater  augmentation,  and  becomes  more  fleshy  ;  projecting 
like  a  mass  of  granulations  from  the  interior  of  the  ovisac,  and 
receiving  blood-vessels  which  pass  into  it  from  the  vascular  membrane 
:that  surrounds  it.     At  the  same  time,  the  wall  of  the  Graafian  follicle 


FERTILIZATION   OF   THE   OVUM.  451 

is  thrown  into  wrinkles,  which  are  directed  towards  the  interior,  so  as 
to  occasion  the  contraction  of  the  cavity ;  and  thus  it  comes  to  he 
entirely  filled  with  the  new  growth,  the  centre  of  which  is  marked  by 
a  sort  of  stelliform  cicatrix.  This  substance  speedily  becomes  of  a 
paler  hue  than  at  first,  and  is  known  from  its  colour  as  the  corpus 
luteum. — The  escape  of  the  ovule  from  the  ovarium  involves  pro- 
cesses which  are  essentially  the  same,  whether  it  be  impregnated  or 
not ;  but  the  subsequent  changes  differ  in  the  two  cases,  so  that  the 
corpus  luteum  which  accompanies  the  pregnant  state  is  usually  a 
much  larger  and  more  highly-organized  body,  than  that  which  is 
found  in  the  ovary  of  the  unimpregnated  female.  This  difference 
may  be  due  in  part  to  the  absence,  in  the  latter  case,  of  that  special 
determination  of  blood  to  the  genital  organs,  which  takes  place  in  the 
former. — It  is  obvious,  then,  that  the  presence  of  a  small  and  imper- 
fect corpus  luteum  in  the  ovary,  merely  indicates  that  an  ovum  has 
been  matured  and  discharged,  and  affords  no  evidence  of  impregna- 
tion or  sexual  intercourse.  The  presence  of  a  large  and  character- 
istic corpus  luteum,  on  the  other  hand,  may  be  regarded  as  affording 
undoubted  evidence  that  impregnation  has  taken  place.  When  fully 
formed,  the  corpus  luteum  may  be  rather  more  than  half  an  inch  in 
one  of  its  diameters,  and  rather  less  in  the  other ;  it  usually  forms  a 
projection  on  the  surface  of  the  ovary,  and  occupies  from  one-fourth, 
to  one-half  of  the  whole  area  of  its  section.  It  is  frequently,  how- 
ever, much  smaller  than  this ;  and  on  the  whole  it  may  be  said  that 
the  presence  of  a  corpus  luteum  as  large  as  a  full-sized  pea,  is  toler- 
ably certain  evidence  of  impregnation.  After  delivery,  the  size  of  the 
corpus  luteum  rapidly  diminishes,  and  in  a  few  months  it  ceases  to  be 
recognisable  as  such ;  the  cicatrix  by  which  the  ovum  has  escaped, 
however,  remains  visible  for  some  time  longer. 

801.  The  increase  of  size  which  is  observable  in  the  ovule  that  is 
being  prepared  for  fecundation,  is  chiefly  due  to  an  augmentation  in  the 
substance  of  the  Yolk ;  and  this  also  becomes  more  firm  and  granular 
than  before.  But  the  most  curious  change  is  that  which  takes  place  in 
the  Germinal  Vesicle ;  for  this,  although  previously  in  the  centre  of  the 
yolk,  now  moves  up  towards  the  side  of  it  which  is  nearest  the  stirface 
of  the  ovary,  and  becomes  flattened  against  the  yolk-bag.  At  the  same 
time,  it  ceases  to  present  its  ordinary  pellucidity  a^d  becomes  obscure; 
and  this  alteration  appears  to  be  due  to  the  development  of  a  brood  of 
young  cells  in  its  interior.  From  the  recent  observations  of  Mr.  New- 
port and  others,  it  would  seem  that  it  then  bursts  and  sets  these  free, 
so  that  they  become  diffused  through  the  yolk ;  and  as  this  change  may 
happen  before  fecundation,  it  must  be  regarded  as  being  preparatory  to 
it,  or  at  any  rate  as  being  independent  of  it. 

802.  The  ova  thus  matured  and  prepared  for  fecundation,  are  dis- 
charged from  the  surface  of  the  ovary  by  the  process  already  described, 
whether  sexual  intercourse  take  place  or  not ;  and  being  received  into 
the  Fallopian  tubes,  they  are  by  them  conducted  towards  the  uterus. 
Their  transmission  may  be  effected  by  a  kind  of  peristaltic  movement 
which  is  observed  to  take  place  in  these  tubes  during  the  periods  of 
heat ;  or,  it  may  be,  by  the  action  of  the  cilia  which  line  them ;  the  di* 


452  OF   GENERATION  AND   DEVELOPMENT. 

rection  of  both  movements  being  the  same,— ^namely,  from  the  ovaries 
towards  the  uterus.  If  in  their  course  they  should  not  receive  the  fer- 
tillizing  influence,  they  appear  soon  to  die  and  to  disintegrate  ;  but  if  they 
should  be  impregnated  by  contact  with  the  spermatic  fluid,  they  almost 
immediately  begin  to  undergo  the  first  of  those  changes,  which  tend  to 
the  production  of  a  new  organism. 

803.  Much  discussion  has  taken  place,  with  regard  to  the  exact  point 
at  which  the  fertilization  of  the  ovulum  takes  place ;  but  this  does  not 
seem  to  be  a  matter  of  much  consequence,  as  we  find  the  order  of  the  difie- 
rent  steps  to  vary  considerably  in  difi*erent  classes  of  animals.  Thus  in 
many  aquatic  Mollusca,  and  even  in  a  large  proportion  of  the  class  of 
Fishes,  there  is  no  act  of  copulation  whatever ;  but  the  spermatic  fluid, 
when  emitted  by  the  male,  is  diffused  through  the  water,  and  fertilizes  the 
ova  which  have  been  deposited  by  the  female  in  his  neighbourhood.  In  the 
Frog,  again,  and  in  other  Reptiles,  the  spermatic  fluid  is  emitted  upon 
the  ova,  at  the  time  that  they  are  being  extruded  by  the  female.  In 
many  Insects  and  Crustacea,  in  which  a  single  congress  often  serves  to 
fertilize  many  thousand  eggs,  the  deposition  of  which  occupies  a  period 
of  several  weeks  or  months,  the  spermatic  fluid  is  received  and  stored 
up  in  a  saccular  dilatation  of  the  oviduct  of  the  female,  which  is  termed 
the  spermo-theea;  and  in  this  manner  it  serves  to  impregnate  the  ova,  as 
they  are  successively  developed,  and  are  conveyed  to  the  outlet  of  the 
oviduct.  In  Birds,  we  find  that  ova  are  often  set  free  from  the  ovarium 
in  a  state  of  full  maturity,  but  without  fertilization ;  and  that  they  re- 
ceive their  additional  layer  of  albumen  and  their  shelly  envelope,  in 
passing  down  the  oviduct,  so  as,  at  the  time  of  tlieir  deposition,  to  diff'er 
in  no  obvious  particular  from  fertile  eggs.  It  is  doubtful,  in  regard  to 
Mammalia,  whether  the  act  of  fertilization  takes  place  before  the  ovum 
has  been  completely  extricated  from  the  ovisac,  or  subsequently  to  its 
finally  quitting  the  ovarium  and  being  received  into  the  Fallopian  tube. 
It  is  quite  certain  that  the  spermatozoa  frequently,  if  not  invariably, 
find  their  way  to  the  surface  of  the  ovary,  being  carried  thither  by 
their  own  spontaneous  movements  ;  and  it  seems  on  the  whole  most  pro- 
bable, that  the  fertilization  of  the  ova  usually  takes  place  before  they 
have  entirely  escaped  from  the  ovisac,  or  whilst  they  are  still  in  the 
commencement  of  the  Fallopian  tube.  It  is  not  unlikely  that  the  place  of 
the  act  of  fecundation  varies,  according  to  the  point  at  which  the  ovule 
and  the  seminal  fluid  first  come  into  contact, — which  may  depend  upon 
the  degree  of  maturity  of  the  ova  at  the  period  of  copulation. 

804.  Everything  indicates  that  the  contact  of  the  Spermatozoon  with 
the  Ovulum  is  the  one  thing  needful  in  the  act  of  fecundation ;  and  there 
is  strong  reason  to  believe,  from  Mr.  Newport's  recent  observations,  that 
when  this  contact  occurs,  the  spermatozoa  undergo  solution ;  and  that  it 
is  in  the  absorption  of  the  product  of  that  solution  into  the  interior  of 
the  ovum  (thus  blending,  as  in  Plants,  the  contents  of  the  "sperm-cell" 
with  those  of  the  "germ-cell"),  that  the  act  of  fecundation  essentially 
consists.  Availing  himself  of  the  agency  of  caustic  potass,  which  has 
been,  found  to  be  a  powerful  solvent  of  the  spermatozoa,  Mr.  N.  applied 
this  agent  to  the  ova  at  determinate  periods  after  the  application  of 
these  bodies,  which  he  had  separated  from  the  liquor  seminis  by  filtra- 


i 


FERTILIZATION   OF  THE   OVUM. 


458 


Fig.  138. 


tion ;  and  he  found  that  when  the  interval  of  time  between  the  one 
application  and  the  other  was  only  one  or  two  seconds,  only  the  early 
stages  of  the  process  took  place,  and  no  embryo  was  produced ;  when 
an  interval  of  five  seconds  was  allowed,  very  few  embryos  were  produced 
from  a  large  number  of  ova ;  but  when  the  interval  was  fifteen  seconds 
or  more,  the  proportion  of  embryos  produced  was  much  greater.  Thus 
it  seems  obvious  that  time  is  an  important  element  in  the  fertilizing 
process ;  and  that  fertilization  may  be  incompletely  efi'ected,  for  want 
of  a  sufficient  penetration  of  the  product  of  the  diffluence  of  the  Sperma- 
tozoa. How  this  product  acts  upon  the  contents  of  the  ovum,  however, 
and  whether  one  or  many  of  the  cells  set  free  by  the  rupture  or  solution 
of  the  germinal  vesicle  are  fertilized  by  it,  have  not  yet  been  ascertained. 
805.  The  first  change  which  can  be  observed  to  be  consequent  upon 
fecundation  in  the  Mammalian  ovum  is  the  "  segmentation"  of  the  yolk; 
the  entire  mass  of  which,  though  previously 
compact  and  uniform,  resolves  itself,  first 
into  two,  then  into  four,  then  into  eight  seg- 
ments (Fig.  138) ;  each  segment  containing  a 
transparent  vesicle,  which  may  be  surmised 
to  be  a  descendant  of  the  original  germ-cell. 
By  a  continuance  of  the  same  process,  the/ 
whole  cavity  of  the  vitelline  sac,  or  zona  pel-/ 
lucida,  becomes  occupied  by  spherical  parti-j  - 
cles  of  yolk  (each  containing  a  pellucid  par-y\\< 
tide),  the  aggregation  of  which  gives  it  a  \ 
mulberry-like  appearance ;  and  by  its  fur- 
ther continuance,  the  component  cells  becom- 
ing more  and  more  minute,  the  mass  comes 
to  present  a  uniform  finely-granular  aspect. 
At  this  stage  it  does  not  appear  that  the  se- 
veral segments  of  the  yolk  have  a  distinct 
enveloping  membrane ;  but  an  envelope  is 
now  formed  around  each  of  them,  converting 
it  into  a  cell,  of  which  the  included  particle 
forms  the  nucleus.  This  happens  first  to  the 
peripheral  portions  of  the  mass ;  and  as  its 
cells  are  fully  developed,  they  arrange  them- 
selves at  the  surface  of  the  yolk  into  a  kind 
of  membrane ;  at  the  same  time  assuming  a 
pentagonal  or  hexagonal  shape  from  mutual 
pressure,  so  as  to  resemble  pavement  epithe- 
lium  (Fig.  139).  As  the  globular  masses  of  (^  ^ 
the  interior  are  gradually  converted  into  cells,  ^^--"^  •     *      •  x^  * 

O''  '        ProgressiTe  stages  m  the  segmenta- 

they  also  pass  to  the  surface  and  accumulate  tion  of  the  vltellus  of  the  Mammalian 
•  1  .!•  •  .1         ji'i  I*    ,1         Ovum: — A,  its  first  division  into  two 

there;  thus  increasmg  the  thickness  oi  the  halves:  b,  subdivision  of  each  half  into 
envelope  already  formed  by  the  more  super-  '^^^J^^Xl^^"'''"'''''''''''''''' 
ficial  layer  of  cells,  while  the  central  part  of 

the  yolk  remains,  filled  only  with  a  clear  fluid,  which  seems  to  be  the 
produce  of  the  liquefaction  of  some  of  the  interior  spherules.  By  this 
process,  the  external  part  of  the  yolk  is  converted  into  a  kind  of  secon- 


454 


OF  GENERATION  AND  DEVELOPMENT. 


dary  envelope,  constituting  the  germinal  membrane  ;  and  as  this  forms 
a  complete  sac  enveloping  the  liquefied  yolk  of  the  interior,  and  as  the 

Fig.  139. 


Latter  stage  in  the  segmentation  of  the  yolk  of  the  Mammalian  Ovum  ; — at  A  is  shown  the  "  mulberry 
mass"  formed  by  the  minute  subdivision  of  the  vitelline  spheres ;  at  B,  a  further  increase  has  brought  its 
sur£B«e  into  contact  wi^  the  vitelline  membrane,  against  which  the  spherules  are  flattened. 

whole  structure  of  the  future  embryo  originates  in  its  substance,  it  has 
been  termed  by  Bischoff  the  blastodermic  vesicle. 

806.  The  Blastodermic  Vesicle  very  soon  after  its  formation,  pre- 
sents at  one  point  an  opaque  roundish  spot,  which  is  produced  by  an 
accumulation  of  cells  and  nuclei  of  less  transparency  than  elsewhere ; 
and  it  is  within  this,  which  is  termed  the  area  germinativa,  that  all  the 
structures  of  the  permanent  organism  originate.  When  seen  in  section, 
this  mass  of  cells  presents  the  aspect  shown  at  Fig.  140,  c.  The  Ger- 
minal Membrane  increases  in  extent  and  thickness  by  the  production 
of  new  cells  ;  and  it  subdivides  into  two.  layers,  which,  although  both  at 
first  composed  of  cells,  soon  present  distinctive  characters,  and  are  con- 
cerned in  very  different  ulterior  operations.  The  outer  one  of  these  is 
commonly  known  as  the  serous  layer,  and  the  inner  as  the  mucous ; 
the  division  is  at  first  most  evident  in  the  neighbourhood  of  the  area 
germinativa ;  but  it  soon  extends  from  this  point,  and  implicates  nearly 
the  whole  of  the  germinal  membrane. 

807.  The  area  germinativa  soon  loses  the  rounded  form  which  it  at 
first  possessed,  and  becomes  first  oval,  and  then  pear-shaped.     Whilst 

Fig.  140. 


Plan  of  early  VUrine  Ovum.    Within  the  external  ring,  or  zona  pellucida,  are  the  blastodermic 
vesicle,  a  /  the  yolk,  h  ;  and  the  incipient  embryo  c. 

this  change  is  taking  place  in  it,  there  gradually  appears  in  its  centre 
a  clear  space,  termed  the  area  pellucida ;  and  this  is  bounded  externally 


GERMINAL  MEMBRANE.  455 

>y  a  more  opaque  circle  (whose  opacity  is  due  to  the  greater  accumula- 
[tion  of  cells  and  nuclei  in  that  part),  which  subsequently  becomes  the 
\mea  vasculosa.  In  the  formation  of  these  two  spaces,  both  the  serous 
[.and  mucous  layers  of  the  germinal  membrane  seem  to  take  their  share-; 
rbut  the  foundation  of  the  vertebral  column  and  nervous  centres  appears 
to  be  laid  chiefly  if  not  entirely  in  the  serous  layer ;  whilst  the  mucous 
is  afterwards  concerned  more  especially  in  the  formation  of  the  nutritive 
apparatus.  Between  these  a  third  layer  subsequently  makes  its  ap- 
pearance ;  which,  as  the  first  vessels  of  the  embryonic  structure  are 
formed  in  it,  is  termed  the  vascular  layer. 

808.  Thus  the  first  development  of  the  Mammalian  embryo  is  into 
a  sac,  enclosing  the  store  of  nutriment  that  has  been  prepared  for  it, — 
in  fact,  a  stomach  ;  and  we  shall  presently  see,  that  it  is  by  the  agency 
of  the  walls  of  this  sac,  that  the  nutrient  materials  which  it  encloses 
are  prepared  for  being  appropriated  to  the  development  of  the  more 
permanent  part  of  the  fabric,  which  is  to  be  evolved  from  the  centre  of 
the  mulberry  mass.  But  we  may  here  stop  to  notice  the  interesting 
fact,  that  the  development  of  the  ovum  in  the  lowest  classes  of  animals 
may  almost  be  said  to  cease  at  this  point ;  the  external  layer  of  the 
germinal  membrane  remaining  as  the  integument ;  the  internal  layer 
becoming  the  lining  of  the  stomach ;  and  the  space  occupied  by  the 
yolk  forming  the  digestive  cavity,  into  which  an  entrance  or  mouth  is 
formed,  by  the  thinning  away  of  the  germinal  membrane  at  a  certain 
point,  round  which  tentacula  or  prolonged  lips  are  usually  developed. 
This  is  the  essential  part  of  the  history  of  development  in  the  simpler 
Polypes ;  and  we  see  how  remarkably  it  corresponds  with  the  history  of 
development  of  the  lower  Cryptogamic  plants,  in  which  the  first-formed 
membranous  expansion,  or  primary  frond,  remains  as  the  permanent 
leaf. — In  the  Mammalia,  on  the  other  hand,  the  greater  part  of  the 
germinal  membrane,  and  of  the  cavity  which  it  forms,  have  a  merely 
temporary  purpose  ;  being  cast  ofi",  when  they  have  performed  their 
function,  like  the  cotyledons  of  Flowering  Plants. 

809.  During  the  time  which  is  occupied  by  these  important  changes, 
the  Ovum  passes  through  the  Fallopian  tubes,  and  makes  its  way  into 
the  Uterus.  During  its  transit  through  the  Fallopian  tubes,  the  Mam- 
malian ovum, — like  the  ovum  of  Birds  in  its  passage  through  the  ovi- 
duct,— receives  an  additional  layer  of  albuminous  matter  secreted  from 
the  walls  of  the  tube ;  and  this  is  surrounded  by  a  fibrous  membrane, 
whose  structure  and  mode  of  formation  have  been  described  on  a  former 
occasion  (§§  181,  182).  The  outer  layer  of  this  envelope,  in  the  egg 
of  the  Bird,  is  further  consolidated  by  the  deposition  of  particles  of  car- 
bonate of  lime  in  its  areolae ;  but  it  undergoes  no  higher  organization. 
In  the  Mammal,  however,  this  new  envelope  (termed  the  Chorion)  is  a 
formation  of  great  importance ;  being  the  medium  through  which  the 
whole  subsequent  nutrition  of  the  embryo  is  derived.  This  is  at  first 
taken  in  by  means  of  a  number  of  villous  processes,  proceeding  from 
the  entire  surface  of  the  Chorion,  and  giving  it  a  spongy  or  shaggy 
appearance ;  these  processes  (which  are  composed  of  nucleated  cells) 
serve  as  absorbing  radicles,  which  draw  in  the  fluids  afforded  by  the 
parent ;  and  they  thus  make  up  for  the  early  exhaustion  of  the  small 


456  OF  GENERATION  AND   DEVELOPMENT. 

supply  of  nutritious  matter  stored  up  in  the  ovum  itself.  The  con- 
tained embryo  appropriates  the  fluid  which  is  thus  imbibed,  by  simple 
absorption  through  its  surface ;  and  thus  it  is  nourished  until  a  more 
special  provision  for  its  development  comes  into  action.  The  structure 
of  this  organ,  termed  the  Placenta,  cannot  be  understood,  until  the 
concurrent  changes  in  the  lining  membrane  of  the  Uterus  have  been 
considered. 

810.  This  membrane,  in  its  natural  condition,  presents  on  its  free 
surface  the  orifices  of  numerous  cylindrical  follicles  ;  which  are  arranged 
parallel  to  each  other,  and  at  right  angles  to  the  surface.  In  the  spaces 
between  these  follicles,  the  blood-vessels  form  a  dense  capillary  network. 
When  impregnation  takes  place,  this  mucous  membrane  swells  and  be- 
comes lax  ;  its  capillaries  increase  in  size  ;  the  follicles  are  developed 
into  glandular  cavities,  and  become  turgid  with  a  white  epithelium  ;  and 
the  interfollicular  spaces  are  crowded  with  nucleated  cells,  which  fill  up 
the  meshes  of  the  capillary  network.  In  this  peculiar  condition,  the 
uterine  mucous  membrane  is  termed  the  Deeidua.  At  a  later  period, 
the  deeidua  may  be  found  to  consist  of  two  distinct  layers ;  the  deeidua 
vera,  lining  the  uterus  ;  and  the  deeidua  reflexa,  covering  the  exterior 
of  the  ovum.  Much  discussion  has  taken  place  with  regard  to  the 
mode  in  which  the  deeidua  reflexa  originates,  and  the  question  cannot 
even  now  be  considered  as  determined.  The  view  recently  put  forth  by 
Coste  is,  perhaps,  as  probable  as  any.  He  considers  that  the  ovum  on 
its  entrance  into  the  uterine  cavity,  is  partly  imbedded  in  its  thick  vas- 
cular lining  membrane,  and  that  this  swells  up  around  it,  like  the 
granulations  around  the  pea  in  an  issue ;  so  that  at  last  the  ovum  be- 
comes completely  invested  by  the  special  envelope  thus  formed,  which 
closes  in  around  it,  constituting  the  deeidua  reflexa,  and  which  is  at 
first  not  in  contact  with  the  deeidua  vera  at  any  part  save  where  it  has 
sprung  from  it.  As  the  ovum  increases  in  size,  the  deeidua  reflexa 
grows  with  it,  and  is  thus  gradually  brought  into  contact  with  the 
deeidua  vera  which  lines  the  uterus,  the  cavity  between  them  being 
obliterated ;  and  at  a  later  period,  the  two  coalesce,  so  that  they  are  no 
longer  distinguishable  from  each  other. 

811.  When  the  ovum  has  arrived  in  the  Uterus,  therefore,  and  the 
villous  tufts  of  its  chorion  are  developed,  these  come  into  contact,  in 
the  first  instance,  with  the  epithelial  layer  which  intervenes  between 
them  and  the  vascular  deeidua.  Through  this  cellular  membrane, 
therefore,  the  ovum  must  derive  its  nutriment  from  the  vascular  sur- 
face ;  and  it  cannot  be  deemed  improbable,  that  its  oflSce  is  to  draw 
from  the  subjacent  vessels  the  materials  which  are  to  serve  for  the 
nutrition  of  the  ovum,  and  to  present  it  to  the  villous  tufts  of  the 
chorion.  Each  of  these,  as  already  mentioned,  is  composed  of  an 
assemblage  of  nucleated  cells,  which  are  found  in  various  stages  of 
development ;  and  the  villus  seems  to  elongate  by  the  development  of 
new  cells  from  the  germinal  spot  at  its  free  extremity,  whilst,  like  the 
spongiole  of  the  plant,  it  draws  in  nutriment  from  the  soil  in  which  it 
is  imbedded.  On  the  other  hand,  the  Deeidua  at  this  early  period, 
appears  to  be  actively  employed  in  preparing  nutriment  for  the 
embryo ;  for  its  cellular  layer  is  so  abundant,  as  to  form  a  bed  into 


FORMATION   OF   DECIDUA,   AND   VILLI   OF   CHORION.  457 

which  the  tufts  of  the  chorion  are  received;  whilst  its  follicles  are 
enlarged  into  glandulse  of  sufficient  size,  to  allow  these  villi  (in  some 
Mammals  at  least)  to  extend  themselves  into  their  interior. — In  its 
earliest  grade  of  development,  as  already  remarked,  the  chorion  and 
its  villi  contain  no  vessels;  and  the  fluid  drawn  in  by  the  tufts  is 
communicated  to  the  embryo,  by  the  absorbing  powers  of  its  germinal 
membrane.  But  when  the  tufts  are  penetrated  by  blood-vessels,  and 
their  communication  with  the  embryo  becomes  much  more  direct,  the 
means  by  which  they  communicate  with  the  parent  are  found  to  be 
essentially  the  same ; — ^namely,  a  double  layer  of  cells,  one  layer 
belonging  to  the  foetal  tuft,  the  other  to  the  vascular  maternal  surface. 
(See  §  819.) 

812.  We  now  return  to  the  Embryo  itself;  the  general  history  of 
whose  development  has  been  already  traced,  up  to  the  period  at  which 
the  cluster  of  cells  in  the  Area  Germinativa  is  about  to  give  origin  to 
the  permanent  structures  of  the  foetus.  The  parts  first  formed  in  the 
embryo  of  Vertebrated  animals,  are  such  as  most  characteristically 
distinguish  them  from  all  others ; — namely,  the  Vertebral  Column,  and 
Spinal  Cord.  The  first  indication  of  these  consists  in  the  formation 
of  what  is  termed  the  primitive  trace^  which  is  a  shallow  groove,  lying 
between  two  oval  ridges  (Fig.  141,  v),  known  as  the  laminoe  dor  sales. 
The  form  of  these  is  changed  with  that  of  the  area  pellucida ;  at  first 
they  are  oval,  then  pear-shaped,  and  at  last  become  of  a  violin-shape. 
At  the  same  time,  they  rise  more  and  more  from  the  surface  of  the 
Area  pellucida,  so  as  to  form  ridges  of  higher  elevation,  with  a  deeper 
groove  between  them;  and  the  summits  of  these  ridges  tend  to 
approach  one  another,  and  gradually  unite,  so  as  to  convert  the  groove 
into  a  tube.  It  is  within  this,  that  the  Cerebro-spinal  Axis  is  after- 
wards formed ;  the  brain  being  developed  in  the  anterior  dilated  por- 
tion, and  the  spinal  cord  in  the  posterior  more  contracted  part.     The 

Fig.  141. 


The  germ  and  surrounding  parts,  from  a  more  advanced  Uterine  Ovum : — 6,  blastoderma,  or  germinal 
membrane ;  a  g,  area  germinativa;  c,  cephalic  extremity  of  the  germ;  v,  first  indications  of  vertebrae ;  q,  cau- 
dal extremity. 

former  remains  unclosed  much  longer  than  the  latter.  The  tube 
within  which  the  neural  axis  is  thus  enclosed,  and  which  is  entirely 
composed  of  nucleated  cells  (Fig.  16),  is  termed  the  Chorda  dorsalis ; 
and  it  retains  its  embryonic  type  in  many  of  the  lower  Fishes,  which 
never  possess  a  true  vertebral  column.     The  elements  of  the  vertebrae 


458 


OF  GENERATION  AND  DEVELOPMENT. 


are  developed  in  a  fibrous  membrane,  with  which  the  chorda  dorsalis 
subsequently  beeomes  invested ;  the  neural  arches  being  the  parts  first 
formed. 

813.  During  the  progress  of  this  change,  another  very  important  one 
is  taking  place,  which  has  reference  to  the  nutrition  of  the  embryo 
during  its  further  development.  This  is  the  formation  of  vessels  in  the 
substance  of  the  germinal  membrane ;  which  vessels  serve  to  take  up 
the  nourishment  supplied  by  the  yolk,  as  well  as  that  derived  from  the 
chorion  externally,  and  to  convey  it  through  the  tissues  of  the  embryo. 
These  vessels  are  first  seen  in  that  part  of  the  vascular  lamina  of  the 
germinal  membrane,  which  immediately  surrounds  the  embryo ;  and 
they  form  a  network,  bounded  by  a  circular  channel,  which  is  known 
under  the  name  of  the  Vascular  Area  (Fig.  142).  This  gradually 
extends  itself,  until  the  vessels  spread  over  the  whole  of  the  germinal 
membrane.  The  vessels  are  probably  formed  by  the  coalescence  of  the 
original  cells  of  the  layer ;  and  the  first  blood-discs  which  they  contain 
seem  to  originate  in  the  nuclei  of  these  cells.  This  network  of  vessels 
serves  to  receive  the  nutritious  matter  contained  in  the  yolk-bag,  and 
to  convey  it  to  the  embryo ;  but  the  act  of  absorption  seems  to  be  per- 
formed here  as  elsewhere,  by  cells,  a  layer  of  which  always  intervenes 
between  the  vascular  layer  and  the  yolk  itself.  These  cells  probably 
correspond  in  function  with  those  of  the  villi  of  the  intestinal  canal  in 
the  adult  (§  243) ;  as  the  vessels  of  the  yolk-bag,  or  temporary  diges- 

Fig.  142. 


^  Vascular  area  of  IbwVs  egg,  at  the  beginning  of  the  third  day  of  incubation  ;~a,  a,  yolk;  6,  b,  b,  b,  venous 
emus  bounding  the  area,  c,  aorta;  d,  punctum  saliens,  or  incipient  heart;  e,  e,  area  pellucida ;  jf^, /,  arteries 
of  the  vascular  area;  g,  g,  veins;  h,  eye. 

tive  cavity,  represent  those  of  the  alimentary  canal,  to  be  afterwards 
developed  from  a  portion  of  it.  The  vessels  of  the  yolk-bag  terminate 
in  two  large  trunks,  which  enter  the  embryo  at  the  point  that  after- 
wards becomes  the  umbilicus,  and  which  are  known  as  the  Omphalo- 
Mesenteric,  Meseraic,  or  Vitelline  vessels  (Fig.  146,  q,  r).  The  first 
movement  of  fluid  takes  place  towards  the  embryo ;  and  this  may  be 
witnessed  before  any  distinct  heart  is  evolved. 


I 


FORMATION   OF   VESSELS   AND   DIGESTIVE   CAVITY. 


459 


814.  The  formation  of  the  Heart  takes  place  in  a  thickened  portion 
of  the  Vascular  layer ;  by  the  liquefaction  of  the  interior  of  a  mass  of 
cells,  of  which  the  exterior  constitute  the  first  walls  of  the  cavity. 
These  gradually  acquire  firmness  and  consistency,  and  are  endowed 
with  a  contractile  power  that  enables  them  to  execute  regular  pulsa- 
tions. In  this  early  condition,  the  heart  is  known  as  the  punctum 
saliens  {d,  Fig.  142).  The  first  appearance  of  the  heart  in  the  Chick 
is  at  about  the  27th  hour ;  the  time  of  its  formation  in  Mammalia  has 
not  been  distinctly  ascertained. 

815.  Concurrently  with  the  formation  of  the  Vascular  system,  the 
production  of  the  permanent  Digestive  cavity  commences.  This  origi- 
nates in  the  separation  of  a  small  portion  of  the  yolk-bag,  lying  imme- 
diately beneath  the  embryo,  from  the  general  cavity,  in  the  following 
manner. — At  about  the  25th  hour  of  incubation,  in  the  Fowl's  egg,  the 
parts  of  the  germinal  membrane  which  lie  beyond  the  extremities,  and 


Fig.  143. 


Fig.  144. 


Diagram  of  Mammalian  Ovum  at  later  stage; 
the  digestive  cavity  beginning  to  be  separated 
from  the  yolk-sac,  and  the  amnion  beginning  to 
be  formed: — a,  chorion;  b,  yolk-sac;  c,  embryo;  d 
and  e,  folds  of  the  serous  layer  rising  up  to  form 
the  Amnion. 


The  Amnion  in  process  of  formation,  by  the 
arching-over  of  the  serous  lamina :— a,  the  cho- 
rion ;  b,  the  yolk-bag,  surrounded  by  serous  and 
vascular  laminae;  c,  the  embryo;  d,  e,  and/,  ex- 
ternal and  internal  folds  of  the  serous  layer, 
forming  the  amnion;  g,  incipient  allantois. 


which  spread  out  from  the  sides  of  the  embryo,  are  doubled-in,  so  as  to 
make  a  depression  upon  the  yolk;  and  their  folded  edges  gradually 
approach  one  another  under  the  abdominal  surface  of  the  embryo,  so  as 
at  last  to  meet  and  enclose  a  cavity,  which  is  at/first  simple  in  its  form, 
but  which  is  subsequently  rendered  more  complex  by  the  prolongation 
and  involution  of  its  walls  in  various  parts,  so  as  to  form  the  stomach 
and  intestinal  tube  (Figs.  143,  144,  145).  This  digestive  cavity  com- 
municates for  some  time  with  the  yolk-bag  (from  which  it  has  been  thus 
pinched-off,  as  it  were),  by  a  wide  opening,  that  is  left  by  the  imperfect 
meeting  of  the  folds  of  the  germinal  membrane  that  constitute  its  walls. 
In  the  Mammalia,  this  orifice  is  gradually  narrowed,  and  is  at  last  com- 
pletely closed ;  and  the  yolk-bag,  thus  separated,  is  afterwards  thrown 
off".  It  may  be  detected,  however,  upon  the  umbilical  cord,  up  to  a  late 
period  of  pregnancy,  and  is  known  as  the  Umbilical  vesicle  (Fig.  146,  t). 
In  Birds,  and  other  oviparous  animals,  the  whole  of  the  yolk-bag  is 


460 


OF   GENERATION  AND  DEVELOPMENT. 


ultimately  drawn  into  the  abdomen  of  the  embryo ;  the  former  gradu- 
ally shrinking,  as  its  contents  are  exhausted ;  and  the  latter  enlarging, 
so  as  to  receive  it  as  a  little  pouch  or  appendage.  In  Fishes,  the 
hatching  of  the  egg  very  commonly  takes  place  before  the  process  has 
been  completed ;  so  that  the  little  Fish  swims  about  with  the  yolk-bag 
hanging  from  its  body. 

816.  Whilst  these  processes  are  going  on  in  the  Vascular  and  Mu- 
cous layers  of  the  germinal  membrane,  a  remarkable  change  is  taking 
place  in  that  portion  of  the  Serous  lamina,  which  surrounds  the  Area 
pellucida.  This  rises  up  on  either  side  in  two  folds  (Fig.  143) ;  and 
these  gradually  approach  one  another,  at  last  meeting  in  the  space 
between  the  general  envelope  and  the  embryo,  so  as  to  form  an  addi- 
tional investment  to  the  latter.  As  each  fold  contains  two  layers  of 
membrane,  a  double  envelope  is  thus  formed  ;  of  which  the  outer  layer 
(Fig.  144,  c?,  e,  and  Fig.  145,  K)  afterwards  adheres  to  the  inner  sur- 
face of  the  chorion,  the  original  yolk-bag,  or  Zona  pellucida,  being  now 
lost  sight  of;  whilst  the  inner  one  (Fig.  144,  /,  /,  and  Fig.  145,  /) 
remains  as  a  distinct  sac,  to  which  the  name  of  Amnion  is  given.  This 
takes  place  during  the  third  day  in  the  Chick  ;  but  the  period  at  which 
it  occurs  in  the  Human  Ovum  has  not  yet  been  clearly  ascertained. 

817.  The  embryo,  like  the  adult,  has  need  of  Respiration ;  in  order 
that  the  carbonic  acid  set  free  in  the  Nutritive  operations  may  be  re- 
moved from  its  fluids.  In  Fishes,  the  surrounding  water  acts  with  suffi- 
cient power  upon  the  vessels  of  the  yolk-bag,  to  produce  the  required 
aeration,  up  to  the  time  when  the  gills  of  the  young  animal  are  ready 
to  come  into  play.  But  in  the  higher  oviparous  animals,  whose  deve- 
lopment proceeds  further  before  they  leave  the  egg,  a  more  special  pro- 
vision is  made  for  the  purpose.  A  bag,  termed  the  allantois,  sprouts 
(as  it  were)  from  the  lower  end  of  the  body  (Fig.  144,  ^) ;  and  gradu- 
ally enlarges,  passing  round  the  embryo  (Fig.  145,  g),  so  as  in  Birds 


Fig.  145. 


Diagram  representing  a  Human  Ovum  in  second  month :— a,  1,  smooth  portion  of  chorion ;  a,  2,  villoxis 
portion  of  chorion ;  k,  k,  elongated  villi,  beginning  to  collect  into  Placenta ;  b,  yolk-sac  or  umbilical  yesicle ; 
c,  embryo ;  /,  amnion  (inner  layer) :  g,  allantois ;  ft,  outer  layer  of  amnion,  coalescing  with  chorion. 


almost  completely  to  enclose  it,  intervening  between  the  germinal  mem- 
brane and  the  shell,  and  receiving  the  direct  influence  of  the  air  that 
penetrates  the  latter.     It  is  thus  the  temporary  lung  of  the  air-breathing 


RESPIRATION   OF   EMBRYO; — ALLANTOIS. 


461 


oviparous  animal ;  and  it  serves  for  the  aeration  of  its  fluids,  up  to  the 
time  when  it  quits  the  egg.  In  the  ovum  of  the  Mammal,  the  chief 
office  of  the  Allantois  is  to  convey  the  vessels  of  the  embryo  to  the  cho- 
rion ;  and  its  extent  bears  a  pretty  close  correspondence  with  the  extent 
of  surface  through  which  the  chorion  comes  into  vascular  connexion  with 
the  decidua, — this  extent  varying  considerably  in  the  different  orders  of 
Mammalia.  Thus  in  the  Carnivora,  whose  placenta  extends  like  a  band 
around  the  whole  ovum,  the  allantois  also  lines  the  whole  inner  surface 
of  the  chorion,  except  where  the  umbilical  vesicle  comes  into  contact 
with  it.  On  the  other  hand,  in  Man  and  the  Quadrumana,  whose  pla- 
centa is  restricted  to  one  spot,  the  allantois  conveys  the  foetal  vessels  to 
one  portion  only  of  the  chorion  (Fig.  146) ;  although,  according  to  Coste, 

Fig.  146. 


Diagram  of  the  Circulation  in  the  Human  Ovum,  at  the  commencement  of  the  formation  of  the  Placenta: 
— a,  venous  sinus,  receiving  all  the  systemic  veins;  &,  right  auricle;  o',  left  auricle;  c,  right  ventricle;  d, 
bulhus  aorticus,  subdividing  into  e,  e',  e",  branchial  arteries;  /,  arterial  trunk  formed  by  their  confluence; 
g,  vena  azygos  superior;  /i,  confluence  of  the  superior  and  inferior  azygos;^,  vena  cava  inferior;  k,  vena 
azygos  inferior;  m,  descending  aorta;  n,  n,  umbilical  arteries  proceeding  from  it;  o,  umbilical  vein;  q, 
omphalo-mesenteric  vein;  r,  omphalo-mesenteric  artery,  distributed  on  the  walls  of  the  vitelline  vesicle  t; 
V,  ductus  venosus;  y,  vitelline  duct;  «,  chorion.   * 

it  completely  surrounds  the  embryo.  When  these  vessels  have  reached 
the  Chorion,  they  ramify  in  its  substance,  and  send  filaments  into  its 
villi ;  and  in  proportion  as  these  villi  form  that  connexion  with  the 
uterine  structure  which  has  been  already  described  {§  811),  do  the  ves- 
sels increase  in  size.  They  then  pass  directly  from  the  foetus  to  the 
chorion ;  and  the  allantois,  which  is  no  longer  of  any  use,  ceases  to 
present  itself  as  a  distinct  sac.  The  lower  part  of  it,  however,  pinched 
off  (as  it  were)  from  the  rest,  remains  as  the  Urinary  bladder ;  and  the 


462  OP  GENERATION  AND  DEVELOPMENT. 

Urachus  or  suspensory  ligament  of  the  latter  represents  the  duct  by 
which  the  Allantois  was  originally  connected  with  the  abdominal  cavity. 

818.  The  connexion  which  is  thus  formed  between  the  Vascular  sys- 
tem of  the  fcetus  and  that  of  the  parent,  is  the  only  one  that  exists  in 
the  lower  Mammalia ;  which  are  thus  properly  designated  as  "  nonpla- 
cental."  Each  villus  of  the  Chorion  contains  a  capillary  loop  ;  this 
is  enclosed  in  a  layer  of  cells  ;  and  this  again  in  a  lamina  of  basement- 
membrane  ; — the  whole  forming  the  fcetal  tuft.  This  comes  into  contact 
with  the  cellular  decidua,  which  lies  upon  the  basement-membrane 
covering  the  vascular  layer  of  the  decidua.  Now  the  Placenta  is  com- 
posed of  these  very  elements,  arranged  in  a  more  complex  manner.  It 
is  formed  by  an  extension  of  the  vascular  tufts  of  the  Chorion  at  certain 
parts  ;  and  a  corresponding  adaptation,  on  the  part  of  the  Uterine  struc- 
ture, to  afford  to  these  an  increased  supply  of  nutritious  fluid.  These 
specially-prolonged  portions  are  scattered,  in  the  Ruminants  and  some 
other  Mammalia,  over  the  whole  surface  of  the  Chorion,  forming  what 
are  termed  the  Cotyledons ;  but  in  the  higher  orders,  and  in  Man,  they 
are  concentrated  in  one  spot,  forming  the  Placenta.  In  some  of  the 
lower  tribes,  the  maternal  and  foetal  portions  of  the  placenta  may  be 
very  easily  separated ;  the  former  consisting  of  the  thickened  decidua  ; 
and  the  latter  being  composed  of  the  prolonged  and  ramifying  vascu- 
lar tufts  of  the  Chorion,  which  dip  down  into  it.  But  in  the  Human 
placenta,  the  two  elements  are  mingled  together  through  its  whole 
substance. 

819.  The  fcetal  portion  of  the  Placenta  consists  of  the  branches  of 
the  umbilical  vessels ;  which  subdivide  at  the  point  at  which  they  enter 
the  mass,  and  form,  by  their  minute  ramifications,  a  large  part  of  its 
substance.  Each  villus  contains  a  capillary  vessel,  which  forms  a 
series  of  loops,  communicating  with  an  artery  on  the  one  side,  and  with 
a  vein  on  the  other;  but  the  same  capillary  may  enter  several  villi, 
before  re-entering  a  larger  vessel.  The  vessels  of  the  villi  (Fig.  147,  g) 
are  covered,  as  in  the  chorion,  by  a  layer  of  cells  (/),  enclosed  in  base- 
ment-membrane (e);  but  the  foetal  tuft  thus  formed  is  enclosed  in  a 
second  series  of  envelopes  (a,  5,  c),  derived  from  the  maternal  portion 
of  the  placenta ;  a  space  {d)  being  left  between  the  two,  however,  at 
the  extremity  of  the  tuft.  The  vascular  tufts  not  unfrequently  extend 
beyond  the  uterine  surface  of  the  placenta,  and  dip  down  into  the  ute- 
rine sinuses,  where  they  are  bathed  in  the  maternal  blood. — The  ma- 
ternal portion  of  the  Placenta  may  be  regarded  as  a  large  sac,  formed 
by  a  prolongation  of  the  internal  coat  of  the  great  uterine  vessels. 
Against  the  foetal  surface  of  this  sac,  the  tufts  just  described  may  be 
said  to  push  themselves,  so  as  to  dip  down  into  it,  carrying  before 
them  a  portion  of  its  thin  wall,  which  constitutes  a  sheath  to  each  tuft. 
In  this  manner,  the  whole  interior  of  the  placental  cavity,  is  intersected 
by  numerous  tufts  of  foetal  vessels,  disposed  in  fringes,  and  bound  down 
by  the  membrane  that  forms  its  proper  wall ;  just  as  the  intestines  are 
covered  and  held  in  their  places  by  the  peritoneum.  Now  as  this  dila- 
tation of  the  uterine  blood-vessels  carries  the  decidua  before  it,  every 
one  of  the  vascular  tufts  that  dips  down  into  it  will  be  covered  with  a 


I 


STRUCTURE   OF  PLACENTA. 


463 


yer  of  the  cellular  structure  of  the  latter  (Fig.  148,  and  Fig.  149,  e) ; 
and  this  will  also  form  a  part  of  all  the  bands  that  connect  and  tie 


Fig.  147. 


Fig.  148. 


Extremity  of  a  Placental  villus : — a,  external  mem- 
brane of  the  villus,  continuous  with  the  lining  mem- 
brane of  the  vascular  system  of  the  mother;  b,  external 
cells  of  the  villus,  belonging  to  the  placental  decidua ; 
c,  c,  germinal  centres  of  the  external  cells ;  d,  the  space 
between  the  maternal  and  foetal  portions  of  the  villus; 
c,  the  internal  membrane  of  the  villus,  continuous  with 
the  external  membrane  of  the  chorion ;  /,  the  internal 
cells  of  the  villus,  belonging  to  the  chorion;  g,  the  loop 
of  umbilical  vessels. 


Portion  of  the  external  mem- 
brane, with  the  external  cells, 
of  a  Placental  villus; — a,  cells 
seen  through  the  membrane ;  &, 
cells  seen  from  within  the  vil- 
lus; e,  cells  seen  in  profile  along 
the  edge  of  the  villus. 


down  the  tufts  (Fig.  149,  g).  The  blood  is  conveyed  into  the  cavity  of 
the  placenta  by  the  "curling  arteries,"  so  named  from  their  peculiar 
course  (Fig.  149,  c),  which  proceed  from  the  arteries  of  the  uterus ;  and 

Fig.  149. 


Diagram  illustrating  the  arrangement  of  the  Placental  Decidua : — a,  decidua  in  contact  with  the  interior 
of  the  uterus;  ft,  venous  sinus  passing  obliquely  through  it  by  a  valvular  opening;  c,  a  curling  artery 
passing  in  the  same  direction;  d,  the  lining  membrane  of  the  maternal  vascular  system,  passing  in  from 
the  artery  and  vein,  lining  the  bag  of  the  placenta,  and  covering  c,  e,  the  foetal  tufts,  passing  on  to  them 
from  their  stems  from  the  foetal  side  of  the  cavity,  also  by  the  terminal  decidual  bars/,/,  from  the  uterine 
side,  and  from  one  tuft  to  the  other  by  the  lateral  bar,  g;  h,  h,  separated  foetal  tufts,  showing  the  internal 
membrane  and  cells,  which,  with  the  loops  of  umbilical  vessels,  constitute  the  true  foetal  portion  of  the 
tufts. 

it  is  returned  by  large,  short,  straight  trunks,  which  pass  obliquely 
through  the  decidua  (Fig.  149,  5),  and  discharge  their  contents  into  the 
great  uterine  sinuses. 

820.  There  is  no  more  direct  communication  between  the  Mother 
and  Foetus  than  this ;  all  the  observations  which  have  been  supposed  to 
prove  a  direct  vascular  continuity,  being  certainly  fallacious.  The 
function  of  the  Placenta  is  manifestly  double.  The  foetal  tufts  draw, 
from  the  maternal  blood,  the  materials  which  are  required  for  the 
nutrition  of  the  embryo, — these  materials  having  been  first  selected 


464  OF  GENERATION  AND  DEVELOPMENT. 

and  partially  elaborated  by  the  two  sets  of  intervening  cells ;  and  in 
this  character,  the  foetal  tufts  resemble  the  villi  of  the  intestinal  surface, 
which  dip  down  into  the  fluids  of  the  alimentary  canal,  and  absorb  the 
nutritive  material  which  they  furnish.  But  the  Placenta  also  serves 
as  a  respiratory  organ ;  aerating  the  blood  of  the  foetus,  by  exposing  it 
to  the  influence  of  the  oxygenated  blood  of  the  Mother ;  and  in  this 
respect  the  foetal  tufts  bear  a  close  correspondence  with  the  gills  of 
aquatic  animals,  bringing  the  blood  into  relation  with  a  surrounding 
fluid  medium  containing  oxygen,  which  is  imbibed  by  the  blood  in 
exchange  for  the  carbonic  acid  given  ofi".  And  it  is  probable,  too, 
that  the  Placenta  is  to  be  regarded  as  an  excreting  organ ;  serving  for 
the  removal,  through  the  maternal  blood,  of  excrementitious  matter, 
whose  continued  circulation  in  the  blood  of  the  foetus  would  be  prejudi- 
cial to  it. 

821.  The  formation  of  the  Human  Placenta  commences  in  the  latter 
part  of  the  second  month  of  utero-gestation ;  during  the  third,  it 
acquires  its  proper  character ;  and  it  subsequently  goes  on  increasing, 
in  accordance  with  the  growth  of  the  ovum.  The  vessels  of  the  Uterus 
undergo  great  enlargement  throughout ;  but  especially  at  the  part  to 
which  the  Placenta  is  attached;  and  the  blood,  in  moving  through 
them,  produces  a  peculiar  murmur,  which  is  usually  audible  with  dis- 
tinctness at  an  early  period  of  pregnancy,  and  which  may  be  regarded 
(when  dile  care  is  taken  to  avoid  sources  of  fallacy)  as  one  of  its  most 
unequivocal  physical  signs.  The  sound  is  most  commonly  heard  near 
the  situation  of  the  Fallopian  tube  of  the  right  side ;  and  it  corresponds 
with  the  pulse  of  the  mother. 

822.  It  would  be  inconsistent  with  the  character  and  objects  of  this 
Treatise,  to  follow,  in  any  detail,  the  history  of  the  development  of  the 
Foetus,  during  its  intra-uterine  life ;  and  a  general  account  of  the  evo- 
lution of  most  of  the  chief  organs,  has  been  given  in  connexion  with 
that  of  their  structure.  The  condition  of  the  Circulating  apparatus, 
however,  at  the  period  of  birth,  deserves  especial  notice.  A  general 
account  of  the  development  of  the  simple  pulsating  trunk,  which  con- 
stitutes its  first  form,  into  the  four-cavitied  heart  of  the  higher  Verte- 
brata,  and  of  the  conversion  of  the  single  trunk  proceeding  from  it, 
with  its  four  pairs  of  branchial  arches,  into  the  aorta  and  pulmonary 
arteries,  with  their  chief  subdivisions,  has  been  already  given  (§  566), 
Up  to  the  time  of  birth,  however,  the  partition  between  the  Auricles  is 
incomplete ;  a  large  aperture,  the  foramen  ovale,  existing  in  it.  There 
is  also  a  direct  communication  between  the  pulmonary  artery  and  the 
aorta,  by  the  ductus  arteriosus;  and  another  direct  channel  between 
the  umbilical  vein  and  the  yena  cava,  by  the  ductus  venosus. 

823.  The  following  is  the  course  of  the  Circulation  of  the  Blood  in 
the  Foetus.  The  fluid  brought  from  the  Placenta  by  the  umbilical  vein 
(Fig.  150,  3),  is  partly  conveyed  at  once  to  the  vena  cava  ascendens,  by 
means  of  the  ductus  venosus  (5),  and  partly  flows  through  two  trunks 
(4,  4),  that  unite  with  the  portal  vein  (7)  returning  the  blood  from  the 
intestines,  into  the  substance  of  the  liver,  thence  to  be  returned  to  the 
vena  cava  by  the  hepatic  vein.  Having  thus  been  transmitted  through  the 
two  great  depurating  organs,  the  placenta  and  the  liver,  the  blood  that 


rCETAL   CIRCULATION. 


465 


enters  the  vena  cava  is  purely  arterial 
in  its  character ;  but  being  mixed  in 
the  vessels  with  the  venous  blood  that 
is  returned  from  the  trunk  and  lower 
extremities,  it  loses  this  character  in 
some  degree,  by  the  time  that  it 
reaches  the  heart.  In  the  right 
auricle,  which  it  then  enters,  it  would 
also  be  mixed  with  the  venous  blood 
which  is  brought  down  from  the  head 
and  upper  extremities  by  the  de- 
scending cava;  were  it  not  that  a 
very  curious  provision  exists,  to  im- 
pede (if  it  does  not  entirely  prevent) 
any  further  admixture.  This  con- 
sists in  the  arrangement  of  the  Eusta- 
chian valve,  which  directs  the  arterial 
current  (that  flows  upwards  through 
the  ascending  cava)  into  the  left  side 
of  the  heart,  through  the  foramen 
ovale,  whilst  it  directs  the  venous 
current  (that  is  being  returned  by  the 
descending  cava)  into  the  right  ven- 
tricle. When  the  ventricles  contract, 
the  arterial  blood  contained  in  the 
left  is  propelled  into  the  ascending 
Aorta,  and  supplies  the  branches  that 
proceed  to  the  head  and  upper  ex- 
tremities, before  it  undergoes  any 
further  admixture  ;  whilst  the  venous 
blood  contained  in  the  right  ventricle, 
is  forced  into  the  Pulmonary  artery, 
and  thence  through  the  ductus  arte- 
riosus (17),  which  is  like  a  continua- 
tion of  its  trunk,  into  the  descending 
aorta,  mingling  with  the  arterial  cur- 
rent which  that  vessel  previously  con- 
veyed, and  thus  supplying  the  trunk 
and  lower  extremities  with  a  mixed 
fluid.  A  portion  of  this  is  conveyed, 
by  the  umbilical  arteries,  to  the  Pla- 
centa ;  in  which  it  undergoes  the 
renovating  influence  of  the  maternal 
blood,  and  from  which  it  is  returned 
in  a  state  of  purity. 

824.  Hence  the  head  and  superior 
extremities,  whose  development  is 
required  to  be  in  advance  of  that 
of  the  lower,  are  supplied  with  blood 
nearly  as  pure  as  that  which  returns 
from  the  placenta ;   whilst  the   rest 

30 


The  Foetal  Circulation : — 1.  The  umbilical  cord, 
consisting  of  the  umbilical  Tain  and  two  um- 
bilical arteries;  proceeding  from  the  placenta 
(2).  3.  The  umbilical  vein  dividing  into  three 
branches;  two  (4,  4)  to  be  distributed  to  the 
liver ;  and  one  (5),  the  ductus  venosus,  which 
enters  the  inferior  vena  cava  (6).  7.  The  portal 
vein,  returning  the  blood  from  the  intestines,  and 
uniting  with  the  right  hepatic  branch.  8.  The 
right  auricle ;  the  course  of  the  blood  is  denoted 
by  the  arrow,  proceeding  from  8,  to  9,  the  left 
auricle.  10.  The  left  ventricle;  the  blood  fol- 
lowing the  arrow  to  the  arch  of  the  aorta  (11), 
to  be  distributed  to  the  branches  given  ofif  by  the 
arch  to  the  head  and  upper  extremities.  The  ar- 
rows 12  and  13,  represent  the  return  of  the  blood 
from  the  head  and  upper  extremities  through 
the  jugular  and  subclavian  veins,  to  the  supe- 
rior vena  cava  (14),  to  the  right  aviricle  (8),  and 
in  the  course  of  the  arrow  through  the  right 
ventricle  (15),  to  the  pulmonary  artery  (16).  17. 
The  ductus  arteriosus,  which  appears  to  be  a 
proper  continuation  of  the  pulmonary  artery; 
the  offsets  at  each  side  are  the  right  and  left 
pulmonary  artery  cut  off;  these  are  of  extremely 
small  size  as  compared  with  the  ductus  arteriO' 
sus.  The  ductus  arteriosus  joins  the  descending 
aorta  (18, 18),  which  divides  into  the  common 
iliacs,  and  these  into  the  internal  iliacs,  which 
become  the  hypogastric  arteries  (19),  and  return 
the  blood  along  the  umbilical  cord  to  the  pla- 
centa; while  the  other  divisions,  the  external 
iliacs  (20),  are  continued  into  the  lower  extremi- 
ties. The  arrows  at  the  terminations  of  these 
vessels  mark  the  return  of  the  venous  blood  by 
the  veins  to  the  inferior  cava. 


466  OF   GENERATION  AND   DEVELOPMENT. 

of  the  body  receives  a  mixture  of  this,  with  what  has  previously  cir- 
culated through  the  system.  The  Pulmonary  arteries  convey  little 
or  no  blood  through  the  lungs ;  the  current  of  blood,  propelled  from  the 
right  ventricle,  passing  directly  onwards  through  the  ductus  arteriosus, 
into  the  aorta. — At  birth,  however,  the  course  of  the  circulation  under- 
goes great  changes,  that  it  may  be  adapted  to  the  new  mode,  in  which 
the  infant  is  henceforth  to  obtain  its  nutrition  and  to  c^arry  on  its  respi- 
ration. As  soon  as  the  lungs  are  distended  by  the  first  inspiration,  a 
portion  of  the  blood  of  the  pulmonary  artery  is  diverted  into  them,  and 
there  undergoes  aeration ;  and,  as  this  proportion  increases,  with  the 
full  activity  of  the  lungs,  the  ductus  arteriosus  gradually  shrinks,  and  its 
cavity  finally  becomes  obliterated.  At  the  same  time,  the  foramen  ovale 
is  closed  by  a  valvular  fold ;  and  thus  the  direct  communication  between 
the  two  auricles  is  cut  off.  When  these  changes  have  been  accom- 
plished, the  circulation,  which  was  before  carried  on  upon  the  plan  of 
that  of  the  higher  Reptiles  (§  563),  becomes  that  of  the  complete  warm- 
blooded animal ;  all  the  blood  which  has  been  returned  in  a  venous  state 
to  the  right  side  of  the  heart,  being  transmitted  through  the  lungs,  be- 
fore it  can  reach  the  left  side,  or  be  propelled  from  its  arterial  trunks. — 
It  is  by  no  means  unfrequent,  however,  for  some  arrest  of  development 
to  prevent  the  completion  of  these  changes ;  and  various  malformations, 
involving  an  imperfect  discharge  of  the  circulating  and  respiratory 
functions,  may  hence  result. 

825.  The  average  length  of  time,  which  elapses  between  Conception 
and  Parturition,  in  the  Human  female,  appears  to  be  280  days,  or  40 
weeks.  There  can  be  little  doubt,  however,  that  Gestation,  may  be 
occasionally  prolonged  for  one,  two,  or  even  three  weeks,  beyond  that 
period ;  such  prolongation  not  being  at  all  unfrequent  amongst  the  lower 
animals  ;  and  numerous  well-authenticated  instances  of  it,  in  the  Human 
female,  being  upon  record.  Upon  what  circumstances  this  departure 
from  the  usual  rule  is  dependent,  has  not  yet  been  ascertained ;  but  it 
is  a  remarkable  circumstance,  ascertained  by  the  observations  of  cattle- 
breeders,  that  the  male  has  an  influence  upon  the  length  of  gestation, — 
a  large  proportion  of  cows  in  calf  by  certain  bulls  exceeding  the  usual 
period,  and  a  small  proportion  falling  short  of  it.  In  such  cases,  we 
must  attribute  the  prolongation  of  the.  period  to  some  peculiarity  in  the 
embryo,  derived  from  its  male  parent. 

826.  The  shortest  period  at  which  Gestation  may  terminate,  consis- 
tently with  the  life  of  the  child,  has  not  yet  been  precisely  ascertained ; 
the  difficulty  of  determining  the  precise  date  of  conception  being  usually 
such,  in  this  case  as  in  the  preceding,  as  to  prevent  the  exact  length 
of  the  Gestation  from  being  known.  Thus,  the  commencement  of  preg- 
nancy being  fixed  by  the  time  of  the  cessation  of  the  Catamenia,  when 
there  is  no  more  definite  guide,  it  is  obvious  that  the  act  of  Conception 
may  have  taken  place  during  any  part  of  the  interval  that  has  elapsed 
since  the  last  monthly  period ;  and  thus  a  doubt  may  exist  as  to  the 
length  of  the  Gestation,  to  the  extent  of,  from  one  to  three  weeks.  There 
are  very  satisfactory  cases  on  record,  in  which,  from  the  degree  of  de- 
velopment of  the  infant  at  birth,  as  well  as  from  other  circumstances, 
it  might  be  certainly  known  not  to  have  attained  26  or  27  weeks,  or 


LENGTH   OF   GESTATION.  467 

little  more  than  six  months ;  and  in  which,  by  careful  treatment,  the 
infant  was  reared  in  a  condition  of  health  and  vigour.     And  there  is 
reason  to  believe,  that  infants  have  lived  for  some  time,  and  might  pro- 
bably have  been  reared  under  better  management,  that  were  born  a»- 
early  as  the  24th  or  25th  week. 

827.  The  act  of  Parturition,  by  which  the  foetus  is  expelled  from  the 
Uterus,  is  accomplished  in  part  by  the  contractile  power  of  the  Uterus 
itself;  and  in  part  by  the  combined  operation  of  the  various  mus- 
cles, which  press  upon  the  abdominal  cavity,  and  which  effect  the  expul- 
sion of  the  faeces  and  urine.  No  definite  account  can  be  given  of  the 
reasons,  why  this  change  should  take  place  at  the  period  which  has  been 
mentioned  as  its  usual  date  ;  but  we  are  as  much  in  the  dark  in  regard 
to  other  periodic  phenomena  of  Animal  life ;  and  we  must  probably 
look  for  its  source  in  the  maturation  of  the  placental  structure,  which 
prepares  it  for  detachment  (like  the  dropping-off  of  a  ripe  fruit),  and  in 
the  complete  evolution  of  the  contractile  tissue  of  the  uterus,  the  con- 
tractions of  which  may  be  considered  to  commence  spontaneously  when 
it  has  attained  a  certain  epoch  in  its  growth,  just  as  do  those  of  the 
heart  in  the  embryo  (§  814).  For  some  days  previously  to  the  com- 
mencement of  labour,  there  is  usually  a  slow  contraction  of  the  fibres 
of  the  fundus  and  body  of  the  uterus,  and  a  yielding  of  those  of  the 
cervix;  so  that  the  child  lies- lower,  and  the  size  of  the  abdomen  dimi- 
nishes. This  slow  contraction  is  probably  not  dependent  upon  any  act 
of  the  nervous  system ;  but  upon  the  direct  excitement  of  the  contrac- 
tility of  the  muscular  substance  of  the  uterus.  When  labour  properly 
commences,  however,  the  Spinal  system  of  nerves  comes  into  play,  and 
the  uterine  contractions  are  of  a  reflex  nature.  As  before,  however, 
the  act  of  contraction  is  confined  to  the  fundus  and  body  of  the  uterus ; 
the  fibres  of  the  cervix  uteri,  and  of  the  vagina,  being  in  a  state  of  re- 
laxation, which  allows  them  to  yield  to  the  pressure  of  the  child's  head. 
In  the  first  stage  of  labour,  the  Uterine  contractions  appear  to  be  alone 
concerned ;  and  it  is  not  until  the  head  of  the  child  is  passing  through 
the  OS  uteri,  and  is  entering  the  vagina,,  that  the  assistance  of  the  ab- 
dominal muscles  is  called  in.  These  act,  in  the  first  instance,  as  in 
ordinary  expiration  ;  but  their  power  is  much  increased  by  the  voluntary 
retention  of  the  breath,  so  that  the  whole  of  their  contractile  force  may 
be  applied  to  the  expulsion  of  the  foetus.  In  a  later  stage  of  labour, 
this  retention  of  the  breath  becomes  involuntary,  during  the  accession  of 
the  "pains;"  and  the  expulsion  of  the  foetus  is  commonly  effected  with 
considerable  force,  especially  if  the  previous  resistance  has  been  con- 
siderable. 

828.  The  same  action  which  expels  the  foetus,  usually  detaches  the 
placenta ;  and  if  the  uterus  contract  with  sufficient  force,  after  this  has 
been  thrown  off,  the  orifices  of  the  vessels  which  communicated  with  it 
are  so  effectually  closed,  that  little  or  no  hemorrhage  from  that  source 
takes  place.  When  efficient  contractions  do  not  occur,  they  may  fre- 
quently be  excited  by  pressure  upon  the  uterus  itself ;  by  the  applica- 
tion of  cold  to  the  abdominal  surface,  to  the  extremities,  and  (in  severe 
hemorrhage)  to  the  entire  body ;  or  by  the  application  of  the  child  to 
the  nipple,  which  will  frequently  at  once  aucceed  in  producing  the  de- 


468  OF  GENERATION  AND  DEVELOPMENT. 


1 


sired  effect.  The  efficacy  of  these  means, — the  latter  in  particular, — 
obviously  depends  upon  the  influence  of  the  spinal  cord  and  its  nerves 
upon  the  muscular  fibres  of  the  uterus ;  the  application  of  cold  to  the 
surface,  or  the  irritation  of  the  nipple,  occasioning  a  reflex  action  in 
the  uterus.  But  it  is  probable  that  this  organ  has  also  considerable  power 
of  contracting,  independently  of  the  nervous  system  ;  thus  there  are 
■well-authenticated  cases  on  record,  in  which  the  foetus  has  been  expelled 
after  the  somatic  death  (§  Qb)  of  the  parent ;  which  must  have  been  in 
consequence  of  the  persistence  of  the  independent  contractility  of  the 
Uterus,  and  the  relaxed  state  of  all  the  parts  through  which  the  child 
had  to  make  its  exit. 

829.  The  cause  of  the  occasional  occurrence  of  the  parturient  efforts 
at  an  unusually  early  period,  is  as  little  understood  as  that  of  their  ordi- 
nary action.  There  are  some  individuals,  in  whom  this  regularly  happens 
at  a  certain  month ;  so  that  it  seems  to  be  an  action  natural  to  them. 
In  many  cases,  however,  it  may  be  traced  to  some  undue  exertion  of 
body,  or  mental  excitement ;  and  not  unfrequently  to  a  general  constitu- 
tional irritability,  which  renders  the  system  liable  to  be  deranged  by 
very  trifling  causes.  Premature  labour  is  always  to  be  prevented,  if 
possible,  being  injurious  alike  to  both  mother  and  child ;  and  for  this  pre- 
vention we  have  chiefly  to  rely  upon  rest  and  tranquillity  of  mind  and 
body,  and  upon  the  careful  avoidance  of  all  those  exciting  cau&es,  which 
are  liable  to  produce  uterine  contractions  by  their  operation  upon  the 
nervous  system ;  whilst,  at  the  same  time,  any  measures  which  will  in- 
vigorate the  body,  without  stimulating  it,  should  not  be  overlooked. 

830.  A  peculiar  preparation  is  made,  in  the  females  of  the  class  Mam- 
malia, for  the  sustenance  of  the  infant  during  a  long  period  after  birth. 
This  consists  in  the  secretion  of  a  fluid,  from  the  glands  termed  Mam- 
mary^ which  contains  all  the  elements  that  are  required  for  the  develop- 
ment of  the  body  of  the  infant,  during  the  first  year.  These  glands 
present  themselves  in  an  almost  rudimentary  state,  in  some  of  the  non- 

placental  animals  of  the  class ;  consisting  only  of 
Fig.  151.  a  few  large  follicles,  which  open  separately  upon 

the  surface  (Fig.  110).  In  the  higher  Mammalia, 
how  ever,  we  find  it  composed  of  vast  numbers  of 
minute  follicles,  clustered  together  upon  excre- 
tory ducts.  The  general  arrangement  of  these, 
in  the  human  subject,  is  seen  in  Fig.  151 ;  and  in 
Fig.  115,  the  character  of  the  follicles  them- 
-,     .   ^.       ,      ,.       ,    selves,  and  of  the  secreting  epithelial  cells  they 

Termination    of    portion    of  .'  ,  °i     i  •    i  •/•    • 

milk-duct  in  follicles;  from  a  coutaiu,  as  sccu  Under  a  much  higher  magniiymg 
CcK)pS"^niarged'four  times.  '  powcr,  has  bccn  already  sliowu.  Each  Mammary 
gland  consists  of  a  number  of  glandulse,  which 
are  held  together  by  areolar  and  fibrous  tissue ;  this  arrangement  may 
probably  have  reference  to  the  mobility,  which  it  is  requisite  that  the 
different  parts  of  the  mass  should  possess,  one  upon  the  other,  in  con- 
sequence of  its  situation  upon  the  pectoralis  muscle.  The  ducts  con- 
verge and  unite  together ;  so  as  at  last  to  form  ten  or  twelve  principal 
trunks,  which  terminate  in  the  nipple.  At  the  base  of  the  nipple,  these 
tubes  dilate  into  reservoirs,  which  extend  beneath  the  areola,  and  to 


MAMMAKY  GLAND.  469 

some  distance  into  the  gland,  when  the  breast  is  in  a  state  of  lactation. 
These,  which  are  much  larger  in  many  of  the  lower  Mammalia  than 
they  are  in  the  Human  female,  seem  to  have  for  their  office  to  contain 
a  store  of  milk,  sufficient  to  supply  the  immediate  wants  of  the  child_ 
when  it  is  first  applied  to  the  breast ;  so  that  it  shall  not  be  disappointed, 
but  shall  be  induced  to  proceed  with  sucking,  until  the  draught  be  oc- 
casioned (§  836). 

831.  The  Mammary  gland  may  be  detected  at  an  early  period  of  foetal 
existence,  and  it  then  presents  no  difference  in  the  male  and  female ; 
and  it  continues  to  grow,  in  each  sex,  in  proportion  to  the  body  at 
large,  up  to  the  period  of  puberty.  At  that  epoch,  however,  the  gland 
begins  to  undergo  a  great  enlargement  in  the  female ;  and  by  the  age 
of  twenty,  it  attains  its  full  size  previous  to  lactation.  Even  then,  how- 
ever, the  milk-follicles  cannot  be  injected  from  the  tubes.  During  preg- 
nancy, the  mammary  glands  receive  a  greatly-increased  quantity  of 
blood.  This  determination  often  commences  very  early  :  and  produces 
a  feeling  of  tenderness  and  distension,  which  is  a  valuable  sign  (where 
it  occurs  in  conjunction  with  others)  of  conception  having  taken  place. 
The  vascularity  of  the  gland  continues  to  increase  during  pregnancy ; 
and,  at  the  time  of  parturition,  its  lobulated  character  can  be  distinctly 
felt.  The  follicles  cannot  be  readily  injected,  however,  until  the  gland 
is  in  a  state  of  complete  functional  activity ;  i.  e.,  during  lactation.—^ 
The  Mammary  gland  of  the  Male  does  not  undergo  this  increase  of  deve- 
lopment, except  under  certain  peculiar  circumstances  to  be  presently 
noticed  (§  836) ;  and  it  remains  a  sort  of  miniature  picture  of  that  of  the 
female,  varying  in  diameter  from  that  of  a  large  pea  to  an  inch  or  even 
two  inches. 

832.  The  Milk,  secreted  by  the  Mammary  glands,  consists  of  Water, 
holding  in  solution  the  peculiar  Albuminous  substance  termed  Oaseine, 
and  various  Saline  ingredients,  together  with  (in  most  cases)  a  certain 
form  of  Sugar ;  and  having  Oleaginous  globules  suspended  in  it.  These 
globules  appear  to  be  surrounded  by  a  thin  pellicle,  which  keeps  them 
asunder,  so  long  as  the  milk  remains  at  rest. — The  existence  of  these 
elements  in  ordinary  Milk,  as  that  of  the  Cow,  is  made  apparent  by  the 
processes  to  which  it  is  subjected  in  domestic  economy.  If  it  be  allowed 
to  stand  for  some  time,  exposed  to  the  air,  a  large  part  of  the  oleagi- 
nous globules  come  to  the  surface,  in  consequence  of  their  inferior  spe- 
cific gravity ;  and  thus  is  formed  the  cream,  whicji  includes  also  a  con- 
siderable amount  of  caseine,  with  the  sugar  and  salts  of  the  milk.  These 
may  be  partly  separated  by  the  continued  agitation  of  the  cream,  as  in 
the  process  of  churning  ;  this,  by  rupturing  the  envelopes  of  the  oil-glo- 
bules, separates  it  into  butter,  formed  by  their  aggregation,  and  butter- 
milk, containing  the  caseine,  sugar,  &c.  A  considerable  quantity  of 
caseine,  however,  is  still  entangled  with  the  oleaginous  matter ;  and  this 
has  a  tendency  to  decompose,  so  as  to  render  the  butter  rancid.  It 
may  be  separated  by  keeping  the  butter  melted  at  a  temperature  of  180°, 
when  the  caseine  will  fall  to  the  bottom,  leaving  the  butter  pure  and 
much  less  liable  to  change ;  an  operation  which  is  commonly  known  as 
the  clarifying  of  butter. — The  Milk,  after  the  cream  has  been  removed, 
still  contains  the  greater  part  of  its  caseine  and  sugar.     If  it  be  k«pt 


470  OF   GENERATION  AND   DEVELOPMENT. 

long  enough,  a  spontaneous  change  takes  place  in  its  composition ;  an 
incipient  change  in  the  caseine  being  the  cause  of  the  conversion  of  the 
sugar  into  lactic  acid ;  and  this  coagulating  the  caseine,  by  precipitating 
it  in  small  flakes.  The  same  precipitation  may  be  accomplished  at  any 
time  by  the  agency  of  various  acids,  especially  the  acetic,  which  does 
not  act  upon  Albumen ;  but  Caseine  cannot  be  coagulated,  like  albu- 
men, by  the  influence  of  heat  alone.  The  most  complete  coagulation 
of  Caseine  is  effected  by  the  agency  of  the  dried  stomach  of  the  calf, 
known  as  rennet;  which  exerts  so  powerful  an  influence  as  to  coagulate 
the  caseine  of  1,800  times  its  weight  of  milk.  It  is  thus  that,  as  in 
the  making  of  cheese,  the  curd  is  separated  from  the  whey ;  the  former 
consisting  chiefly  of  the  caseine ;  whilst  the  latter  contains  a  large 
proportion  of  the  saline  and  saccharine  matter,  which  entered  into  the 
original  composition  of  the  milk.  These  may  be  readily  separated  by 
evaporation. 

833.  The  principal  characters  of  Caseine  have  been  already  stated 
(§  172). — The  Oleaginous  matter  consists,  like  the  fats  in  general,  of 
the  two  substances,  elaine  and  stearine ;  but  it  also  contains  another 
substance  peculiar  to  it,  which  is  termed  hutyrine.  This  last  (to  which 
the  characteristic  smell  and  taste  of  butter  are  due)  is  conveyed  by 
saponification  into  three  volatile  acids,  of  strong  animal  odour,  to  which 
the  names  of  butyric,  capric,  and  caproic  acids  have  been  given.  This 
change  may  be  eff'ected,  at  any  period,  by  treating  the  butyrine  with 
alkalies ;  but  it  may  also  take  place  by  spontaneous  decomposition,  which 
is  favoured  by  time  and  moderate  warmth. — The  Sugar  of  Milk  is  pecu- 
liar as  containing  nearly  12  per  cent,  of  water :  so  that  it  may  be  con- 
sidered as  really  a  hydrate  of  sugar.  It  is  nearly  identical  in  its  com- 
position with  starch ;  and  may,  like  it,  be  converted  into  true  sugar  by 
the  agency  of  sulphuric  acid.  But  it  is  chiefly  remarkable  for  its 
proneness  to  conversion  into  lactic  acid,  under  the  influence  of  a  fer- 
ment or  decomposing  azotized  substance. — The  Saline  matter  contained 
in  Milk  appears  to  be  nearly  identical  with  that  of  the  blood ;  with  a 
larger  proportion,  however,  of  the  phosphates  of  lime  and  magnesia, 
which  amount  to  2  or  2J  parts  in  1000.  These  are  held  in  solution 
chiefly  by  the  Caseine,  which  has  a  remarkable  power  of  combining 
with  them. 

834.  Thus  ordinary  Milk  contains  the  three  classes  of  organic  prin- 
ciples, which  form  the  chief  part  of  the  food  of  animals, — namely,  the 
albuminous,  the  saccharine,  and  the  oleaginous  j  together  with  the  mi- 
neral elements,  which  ^are  required  for  the  development  and  consolida- 
tion of  the  fabric  of  the  infant.  It  would  appear,  however,  that  the 
combination  of  all  these  is  not  necessary ;  but  rather  has  reference  to 
the  composition  of  the  food  on  which  the  animal  is  destined  to  be  after- 
wards supported.  Thus  it  has  been  lately  shown  that,  in  the  Carnivora, 
the  milk  contains  no  sugar ;  which  principle  is  altogether  wanting  in 
the  food  of  the  adult.  Amongst  the  difi'erent  species  of  Herbivorous 
animals,  the  proportion  of  the  several  ingredients  varies  considerably  ; 
and  it  is  also  liable  to  considerable  variation  in  accordance  with  the 
nature  of  the  food,  the  amount  of  exercise  taken  by  the  animal  that 
afibrds  it,  and  other  circumstances.     Thus  in  the  milk  of  the  Cow,  Goat, 


COMPOSITION   OF   MILK.  471 

and  Sheep,  the  average  proportions  of  Caseine,  Butter,  and  Sugar  are 
nearly  the  same  one  with  another,  each  amounting  to  from  3  to  5  per 
cent.  In  the  milk  of  the  Ass  and  Mare,  on  the  other  hand,  the  pro- 
portion of  Caseine  is  under  2  per  cent.,  the  oleaginous  constituents  are 
scarcely  traceable,  whilst  the  sugar  and  allied  substances  rise  to  nearly 
9  per  cent.  In  the  human  female,  the  saccharine  and  oleaginous  ele- 
ments are  both  present  in  large  amount ;  whilst  the  Caseine  forms  a 
moderate  proportion. — The  proportion  of  the  saccharine  and  oleaginous 
elements  appears  to  be  considerably  affected  by  the  amount  in  which 
these  are  present  in  the  food ;  and  by  the  degree  in  which  the  quantity 
ingested  is  consumed  by  the  respiratory  process.  Thus,  a  low  external 
temperature,  and  out-door  exercise,  by  increasing  the  production  of 
carbonic  acid  from  the  lungs,  occasion  the  consumption  of  the  oleagi- 
nous and  saccharine  matters,  which  might  otherwise  pass  into  the 
milk,  and  thus  diminish  the  amount  of  cream.  On  the  other  hand,  exer- 
cise favours  the  secretion  of  caseine  ;  which  would  seem  to  show,  that 
this  ingredient  is  derived  from  the  disintegration  of  the  azotized  tissues. 
Thus  in  Switzerland,  the  cattle  which  pasture  in  exposed  situations,  and 
which  are  obliged  to  use  a  great  deal  of  muscular  exertion,  yield  a  very 
small  quantity  of  butter,  but  an  unusually  large  proportion  of  cheese ; 
yet  the  same  cattle,  when  stall-fed,  give  a  large  quantity  of  butter,  and 
very  little  cheese. 

835.  The  Milk  first  secreted  after  parturition,  known  as  the  Colos- 
trum, is  very  different  from  ordinary  milk,  and  possesses  a  strongly- 
purgative  action,  which  is  useful  in  clearing  the  bowels  of  the  infant, 
from  the  various  secretions  which  have  accumulated  in  them  at  birth, 
constituting  the  meconium.  The  Colostrum,  when  examined  with  the 
Microscope,  is  found  to  contain  a  multitude  of  large  yellow  granulated 
corpuscles  ;  each  of  which  seems  composed  of  a  number  of  small  grains 
aggregated  together.  The  Colostric  character  is  sometimes  retained 
for  some  time  after  birth,  and  severely  affects  the  health  of  the  infant. 
This  may  happen  without  any  peculiarity  in  the  ordinary  characters 
of  the  secretion,  which  has  all  the  appearance  of  healthy  milk  ;  but  th4 
Microscope  at  once  detects  the  difference,  by  the  presence  of  the  colos- 
tric corpuscles. 

836.  The  formation  of  this  Secretion  is  influenced  by  the  Nervous 
system,  to  a  greater  degree,  perhaps,  than  that  of  any  other.  The 
process  may  go  on  continuously,  to  a  slight  degree,  during  the  whole 
period  of  lactation ;  but  it  is  only  in  animals  that  have  special  reser- 
voirs for  the  purpose,  that  any  accumulation  of  the  fluid  can  take 
place.  In  the  Human  female,  as  we  have  seen,  these  are  so  minute  as 
to  hold  but  a  trifling  quantity  of  milk ;  and  the  greater  part  of  the 
secretion  is  actually  formed  whilst  the  child  is  at  the  breast.  The 
irritation  of  the  nipple  produced  by  the  act  of  suction,  and  the  mental 
emotion  connected  with  it,  concur  to  produce  an  increased  flow  of 
blood  into  the  gland,  which  is  known  to  Nurses  as  the  draught ;  and 
thus  the  secretion  is  for  the  time  greatly  augmented.  The  draught 
may  be  produced  simply  by  the  emotional  state  of  mind,  as  by  the 
thought  of  the  child  when  absent ;  and  the  irritation  of  the  nipple  may 
alone  occasion  it ;  but  the  two  influences  usually  act  simultaneously. 


4Y2  OF  GENERATION  AND  DEVELOPMENT. 

The  most  remarkable  examples  of  the  influence  of  such  stimuli  on  the 
Mammary  secretion,  are  those  in  which  milk  has  been  produced  by 
girls  and  old  women,  and  even  by  men,  in  quantity  sufficient  for  the 
support  of  an  infant.  The  application  of  the  child  to  the  nipple  in 
order  to  tranquillize  it,  the  irritation  produced  by  its  efibrts  at  suction, 
and  the  strong  desire  to  furnish  milk,  seem  in  the  first  instance  to 
occasion  an  augmented  nutrition  of  the  gland,  so  that  it  becomes  fit  for 
the  performance  of  its  function  ;  and  then  to  produce  in  it  that  state 
of  functional  activity,  the  result  of  which  is  the  production  of  Milk. 

837.  It  is  not  only  in  this  way^  that  the  Mammary  secretion  is 
influenced  by  the  condition  of  the  mind ;  for  it  is  peculiarly  liable  to 
be  afiected  as  to  quality,  by  the  habitual  state  of  the  feelings,  or  even 
by  their  temporary  excitement.  Thus  a  fretful  temper  not  only  lessens 
the  quantity  of  milk,  but  makes  it  thin  and  serous,  and  gives  it  an 
irritating  quality ;  and  the  same  effect  will  be  produced  for  a  time  by  a 
fit  of  anger.  Under  the  influence  of  grief  or  anxiety,  the  secretion  is 
either  checked  altogether,  or  it  is  diminished  in  amount,  and  deteriorated 
in  quality.  The  secretion  is  usually  checked  altogether  by  terror ;  and 
under  the  influence  of  violent  passion,  it  may  be  so  changed  in  its 
characters,  as  to  produce  the  most  injurious  and  even  fatal  consequences 
to  the  infant.  So  many  instances  are  now  on  record,  in  which  children, 
that  have  been  suckled  within  a  few  minutes  after  the  mothers  have 
been  in  a  state  of  violent  rage  or  terror,  have  died  suddenly  in  convul- 
sive attacks,  that  the  occurrence  can  scarcely  be  set  down  as  a  mere 
coincidence;  and  certain  as  we  are  of  the  deleterious  effects  of  less 
severe  emotions  upon  the  properties  of  the  milk,  it  does  not  seem  un- 
likely that,  in  these  cases,  the  bland  nutritious  fluid  should  be  converted 
into  a  poison  of  rapid  and  deadly  operation. 

838.  Of  the  quantity  of  Milk  ordinarily  secreted  by  a  good  Nurse, 
it  is  impossible  to  form  any  definite  idea ;  as  the  amount  which  can  be 
artificially  drawn,  affords  no  criterion  of  that  which  is  ordinarily  secreted 
at  the  time  of  the  draught.  The  quantity  which  can  be  squeezed  from 
either  breast  at  any  one  time,  and  which,  therefore,  must  have  been 
contained  in  its  tubes  and  reservoirs,  is  about  two  ounces.  The  amount 
secreted  will  depend  upon  several  circumstances ;  such  as  the  nature 
and  amount  of  the  ingesta ;  the  state  of  bodily  health ;  and  the  condi- 
tion of  the  mind.  An  adequate  but  not  excessive  supply  of  nutritious 
food,  in  which  the  farinaceous,  oleaginous,  and  albuminous  principles 
are  duly  blended ;  a  vigorous  but  not  plethoric  constitution,  regular 
habits,  and  moderate  exercise,  together  with  a  cheerful  and  tranquil 
temper,  altogether  produce  the  most  beneficial  influence  upon  the 
secretion.  It  is  seldom  that  stimulating  liquors,  -^hich  are  so  commonly 
indulged  in,  are  anything  but  prejudicial;  but  the  unmeasured  con- 
demnation of  them,  in  which  some  writers  have  indulged,  is  certainly 
injudicious  ;  as  experience  amply  demonstrates  the  improvement  in  the 
condition  both  of  mother  and  infant,  which  occasionally  results  from 
the  moderate  employment  of  them. — In  the  administration  of  medicines 
to  the  mother,  it  is  very  desirable  that  the  tendency  of  soluble  saline 
substances  to  pass  into  the  milk,  and  thus  to  affect  the  child,  should  be 
borne  in  mind.     The  vegetable  substances  used  in  medicine  seem  to 


GENERAL  FUNCTIONS   OF  NERVOUS   SYSTEM.  473 

have  mucli  less  disposition  to  pass  off  by  this  secretion ;  and  they  are 
consequently  to  be  preferred  during  lactation. 

839.  From  the  close  correspondence  which  exists,  between  the  ele- 
ments of  the  Milk  and  those  of  the  Blood,  it  is  evident  that  we  cannot 
expect  to  trace  the  existence  of  the  former,  as  such,  in  the  circulating 
current.  It  is  interesting,  however,  to  remark,  that  a  preparation 
appears  to  be  taking  place  in  the  laboratory  of  the  system,  for  the  pro- 
duction of  this  secretion,  long  before  the  period  of  parturition.  The 
Urine  of  pregnant  women  almost  invariably  contains  a  peculiar  sub- 
stance termed  kiestine,  which  is  nearly  related  to  caseine,  and  which 
disappears  from  the  urine  as  soon  as  lactation  has  fully  commenced. 
It  would  seem,  therefore,  that  a  compound  of  this  nature  is  in  course 
of  preparation  during  pregnancy;  and  that  it  is  eliminated  by  the 
kidney,  until  the  Mammary  Gland  is  prepared  for  the  active  perform- 
ance of  its  functions. — That  the  Kidney  may  relieve  the  system  from 
the  accumulation  of  other  constituents  of  the  mammary  secretion, 
appears  from  a  case  recently  put  on  recond ;  in  which  the  urine  of  a 
parturient  female,  who  did  not  suckle  her  infant,  was  found  to  contain 
a  considerable  quantity  of  butyric  acid,  during  several  days.  There  can 
be  no  doubt  that,  in  ordinary  states  of  the  system,  this  secretion  can- 
not be  required  for  the  depuration  of  the  blood,  since  it  does  not  occur 
in  the  male  at  all,  and  is  present  in  the  female  at  particular  times  only. 
But  these  facts  afford  ground  to  believe  that,  when  the  process  is  going 
on,  certain  products  are  generated  in  the  system,  which  are  not  found 
there  at  other  times.  And  it  is  quite  certain  that  the  sudden  checking 
of  the  secretion,  or  the  reabsorption  of  the  fluid  already  poured  out, 
occasioning  an  accumulation  of  these  substances  in  the  circulating  cur- 
rent, may  give  rise  to  very  injurious  consequences.  Some  very  curious 
instances  are  on  record,  in  which  a  transference  of  the  secreting  power 
to  some  other  surface  has  taken  place  under  such  circumstances ;  so  as 
to  relieve  the  system  from  the  accumulation  in  question. 


CHAPTER  XII. 

OF  THE  NERVOUS  SYSTEM  AND  ITS  ACTIONS. 

1.    General  View  of  the  operations,  of  which  the  Nervous  System  is  the 

instrument. 

840.  We  have  now  considered  the  entire  series  of  those  operations, 
which  make  up  the  vegetative  or  organic  life  of  the  Animal ;  including  those 
functions  by  which  the  germ  is  prepared,  by  which  it  is  nourished  until 
it  can  be  left  to  its  own  powers,  by  which  its  continued  development  is 
effected  until  the  fabric  characteristic  of  the  adult  has  been  built  up, 
and  by  which  the  normal  constitution  is  maintained  through  a  length- 
ened period, — so  long  as  the  necessary  materials  are  supplied,  and  no 


474  OF   THE   NERVOUS   SYSTEM    AND   ITS   ACTIONS. 

check  or  hindrance  is  interposed,  by  externf^l  influences,  to  that  regular 
sequence  of  changes,  on  which  the  continuance  of  its  powers  depends. 
In  this  survey  it  will  have  been  perceived,  that  the  essential  parts  of 
these  operations  are,  in  Animals  as  in  Plants,  completely  independent 
of  the  influence  of  that  which  constitutes  the  peculiar  endowment  of 
Animals ;  namely,  the  Nervous  System. 

a.  The  Reduction  of  the  food  in  the  Stomach,  by  the  solvent  power 
of  the  gastric  fluid,  is  a  purely  chemical  operation,  with  which  the  Ner- 
vous System  has  nothing  whatever  to  do,  excepting  that  it  perhaps 
accelerates  the  process,  by  stimulating  the  Muscular  coat  of  the  stomach 
to  that  peculiar  series  of  contractions,  which  keeps  the  contents  of  the 
cavity  in  continual  movement,  and  favours  the  action  of  the  solvent 
upon  it. 

h.  In  the  process  of  Absorption^  by  which  the  nutritive  materials, 
with  other  substances,  are  introduced  into  the  vessels,  the  Nervous  Sys- 
tem has  no  participation ;  this  being  a  purely  vegetative  operation,  partly 
dependent  upon  the  simple  physical  conditions  which  produce  Endos- 
mose,  and  partly  on  a  process  of  cell-growth. 

c.  The  Assimilation  of  the  new  material,  efi^ected,  as  we  have  seen 
reason  to  believe,  by  another  set  of  independent  cells,  can  receive  but 
little  influence  from  the  Nervous  System,  and  is  obviously  capable  of 
taking  place  without  its  aid. 

d.  The  Circulation  of  the  Blood,  again,  though  dependent  in  part 
upon  the  impulsive  power  of  a  Muscular  organ,  the  Heart,  is  not  on  that 
account  brought  into  closer  dependence  upon  the  Nervous  System ;  for 
we  have  seen  that  the  contractions  of  the  heart  result  from  its  own 
inherent  powers,  so  as  to  continue  after  it  has  been  completely  detached 
from  the  body ;  and  that  the  capillary  power,  which  is  the  chief  agent 
in  the  movement  of  the  blood  in  the  lower  animals,  and  which  exerts  an 
important  subsidiary  action  in  the  higher,  is  the  result  of  the  exercise 
of  certain  affinities  between  the  blood  and  the  surrounding  tissues,  in 
which  the  Nervous  System  can  have  no  immediate  concern. 

e.  The  act  of  Nutrition,  in  which  every  tissue  draws  from  the  circu- 
lating blood  the  materials  for  its  own  continued  growth  and  develop- 
ment, and  by  which  it  incorporates  these  with  its  own  substance,  is  but 
a  continuance  of  the  same  kind  of  operation,  as  that  which  takes  place 
in  the  early  development  of  the  embryo,  long  anteriorly  to  the  first 
appearance  of  the  nervous  system, — namely,  a  process  of  cell-develop- 
ment and  metamorphosis,  which  must  be,  from  its  very  nature,  indepen- 
dent of  Nervous  agency. 

/.  The  same  may  be  said  of  the  Secreting  operation  in  general ;  for 
this  essentially  consists  in  the  separation  of  certain  products  from  the 
blood,  by  cells  situated  upon  free  surfaces ;  which  thus  remove  those 
products  from  the  interior  of  the  fabric. 

'9'  -^^^  *^®  interchange  of  oxygen  and  carbonic  acid,  which  takes 
place  between  the  atmosphere  and  the  venous  blood,  when  brought  into 
mutual  relation  in  the  lungs,  and  which  is  the  essential  part  of  the  func- 
tion of  Respiration,  is  an  operation  of  a  merely  physical  character,  with 
which  the  Nervous  system  can  have  no  direct  concern. 

h  Finally,  the  development  of  the   "  sperm-germ-cells"  in  the  one 


GENERAL   FUNCTIONS   OF   NERVOUS   SYSTEM-  475 

sex,  and  of  the  ova  containing  germ-cells  in  the  other,  the  subsequent 
fertilization  of  the  latter  by  the  former,  and  the  changes  consequent 
upon  that  act,  together  making  up  the  function  of  Creneration,  may  be 
all  regarded  as  modifications  of  the  ordinary  Nutritive  processes ;  and 
are  effected,  like  these,  by  the  inherent  powers  of  the  parts  concerned 
in  them,  at  the  expense  of  the  materials  supplied  by  the  blood,  without 
any  direct  dependence  upon  the  Nervous  system. 

841.  Still,  although  the  various  processes,  which  make  up  the  essen- 
tial part  of  the  nutritive  operations,  in  Animals  as  in  Plants,  are  no 
more  dependent  on  any  peculiar  influence  derived  from  a  Nervous  sys- 
tem, in  the  former,  than  they  are  in  the  latter,  it  must  be  evident,  from 
the  details  already  given,  that  there  must  be  in  Animals  various  acces- 
sory changes,  which  are  requisite  for  the  continuance  of  the  former,  and 
which  can  only  be  effected  by  the  peculiar  powers  with  which  Animals 
are  endowed. — Thus,  to  commence  with  Digestion  ;  this  preliminary 
process,  which  the  nature  of  the  food  of  the  plant  renders  unnecessary 
for  its  maintenance,  can  only  be  accomplished  by  the  introduction  of  the 
food  into  a  cavity  or  sac,  in  which  it  may  be  submitted  to  the  action  of 
the  solvent  fluid.  The  operation  of  grasping  and  swallowing  the  food, 
wherever  it  is  performed,  is  accomplished  through  the  agency  of  the 
Nervous  system ;  and  if  it  be  checked  by  the  loss  of  Nervous  power,  the 
Digestive  process  must  cease  for  want  of  material. — So,  again,  although 
interchange  of  gaseous  ingredients  between  the  atmosphere  and  the 
circulating  fluid  may  take  place  with  sufiicient  energy  in  Plants  and  the 
lower  Animals,  through  the  mere  exposure  of  the  general  surface  to  the 
atmosphere,  yet  we  find  that,  in  all  the  higher  Animals,  certain  move- 
ments are  requisite,  for  the  continual  renewal  of  the  air  or  water  which 
are  in  contact  with  one  side  of  the  respiratory  surface,  and  of  the  blood 
which  is  in  relation  with  the  other :  for  the  direction  of  which  move- 
ments a  Nervous  system  is  requisite. — In  the  excretory  processes, 
moreover,  the  removal  of  the  effete  matters  from  the  body  can  only  be 
accomplished,  in  the  higher  Animals,  by  certain  combined  movements ; 
the  object  of  which  is,  to  take  up  the  products  that  are  separated  by 
the  action  of  the  proper  secreting  cells,  and  to  carry  them  to  the  exterior 
of  the  body,  there  to  be  set  free  ;  and  these  combined  movements  can 
only  be  effected  by  the  agency  of  the  Nervous  system. — Lastly,  in  the 
act  of  Reproduction,  the  arrangement  of  the  sexual  organs  in  Animals 
requires  that  a  certain  set  of  movements  should  be  adapted  to  bring 
together  the  contents  of  the  "sperm-cells"  of  the  male,  and  of  the  "germ- 
cells"  of  the  female  ;  and  also  for  the  expulsion  of  the  ovum  from  the 
body  of  the  latter,  in  a  state  of  more  or  less  advanced  development. 
For  these  movements  a  special  arrangement  is  made,  in  the  construction 
of  the  Nervous  system,  and  in  the  application  of  its  peculiar  powers. 

842.  Thus  we  see  that,  although  the  Organic  functions  of  the  Animal 
are  essentially  independent  of  the  Nervous  System,  this  system  affords 
the  conditions  which  are  requisite  for  their  continued  maintenance ; 
being  the  instrument  whereby  the  muscles  are  called  into  action  for  the 
performance  of  the  various  combined  actions,  that  constitute  the  mecha- 
nism (so  to  speak)  by  which  the  Vegetative  part  of  the  fabric  is  com- 
bined with  the  Animal  portion  of  the  organism.    We  are  not  to  suppose, 


476  OF  THE  NERVOUS   SYSTEM  AND   ITS   ACTIONS. 

however,  that  every  movement  which  takes  place  in  the  Animal  body  is 
dependent  upon  the  Nervous  System  ;  for  we  have  seen  that  the  Muscu- 
lar tissue  may  be  employed  to  perform  contractions  excited  by  stimuli 
applied  to  itself,  and  that  it  may  thus  execute  a  set  of  movements  in 
which  the  nervous  system  has  no  direct  participation.  And  it  is  desirable 
that  the  Student  should  observe,  that  these  are,  in  all  instances,  those 
most  directly  connected  with  the  Vegetative  functions,  and,  at  the  same 
time,  those  of  the  simplest  and  most  straightforward  character. — Thus, 
the  peristaltic  movement,  by  which  the  alimentary  and  fsecal  matters 
are  propelled  along  the  Intestinal  tube,  results  from  the  direct  excite- 
ment of  the  contractility  of  its  muscular  walls,  and  is  entirely  indepen- 
dent of  Nervous  agency ;  and  this  movement  is  accomplished  by  the 
successive  contraction  of  the  different  fasciculi  surrounding  the  tube, 
which  take  up  (as  it  were)  each  others'  action  (§  352).  So  again,  'the 
successive  contractions  and  dilatations  of  the  cavities  of  the  Heart, 
which  perform  so  important  a  part  in  the  Circulation  of  the  blood,  are 
the  result  of  the  properties  inherent  in  that  organ  ;  the  muscular  fibres 
of  which  are  excited  to  a  peculiar  rhythmical  and  consentaneous  con- 
traction, by  the  flow  of  blood  into  the  cavities  when  dilating.  More- 
over, in  the  Excretory  ducts  of  various  glands,  we  find  a  Muscular  coat, 
by  which  the  fluids  secreted  in  the  glands  are  propelled  towards  their 
outlet  on  the  exterior  of  the  body,  or  on  one  of  its  free  internal  surfaces. 

843.  In  these  instances,  then,  we  observe  that  .the  simple  Contractility 
of  Muscular  structure,  excited  by  direct  stimulation,  is  applied  to  effect 
the  movements  most  closely  connected  with  the  Organic  functions.  With 
the  processes,  therefore,  which  take  place  in  \hQ  'penetralia  of  the  system, 
the  Nervous  System  has  no  direct  concern.  Its  ofiice  is  to  guard  the 
portals  for  entrance  and  exit ;  and  to  fill  those  chambers,  which  admit 
the  new  materials  from  the  external  world ;  or  to  empty  the  receptacles, 
which  collect  from  the  interior  of  the  system  the  effete  matters  that  are 
to  be  cast  out  from  it.  And  we  find  that,  for  these  ofiices,  the  Nervous 
system  is  employed  in  its  very  simplest  mode  of  operation  ; — that  which 
does  not  involve  Sensation,  Intelligence,  Will,  or  even  Instinct  (in  the 
proper  sense  of  that  term),  but  which  may  take  place  independently  of 
all  consciousness, — by  the  simple  reflexion  of  an  impression,  conveyed 
to  a  ganglionic  centre  by  one  set  of  fibres  proceeding  towards  it  from 
the  circumference,  along  another  set  which  passes  from  it  to  the  mus- 
cles, and  calls  them  into  operation  (§  394).  This  reflex  function,  there- 
fore, is  the  simplest  application  of  the  Nervous  System  in  the  Animal 
body.  We  shall  presently  see  reason  to  believe,  that  a  very  large  pro- 
portion of  the  movements  of  many  of  the  lower  animals  are  of  this  reflex 
character ;  and  that  they  are  not  necessarily  accompanied  by  sensation, 
although  this  may  usually  be  aroused  by  the  same  cause  which  produces 
them.  As  we  rise,  however,  in  the  scale  of  Animal  existence,  we  find 
the  reflex  movements  forming  a  smaller  and  smaller  proportion  of  the 
whole ;  until,  in  Man,  they  constitute  so  limited  a  part  of  the  entire 
series  of  movements  of  which  the  Nervous  system  is  the  agent,  that  their 
very  existence  has  been  overlooked. 

844.  But  the  main  purpose  of  the  Nervous  System  is  to  serve  as  the 


DEPENDENCE   OF   MENTAL   ACTIONS   UPON   SENSATIONS.  477 

instrument  of  the  PsyeJiical^  powers,  which  are  the  distinguishing 
attribute  of  the  Animal.  It  has  been  already  pointed  out,  that  the  pos- 
session of  Consciousness  (or  of  the  capability  of  receiving  sensations), 
and  the  power  of  executing  Spontaneous  Movements  (that  is,  movements 
which  are  not  immediately  dependent  upon  external  stimuli),  constitute 
the  essential  features  in  which  the  Animal  differs  from  the  Plant.  All 
the  other  differences  in  structure,  that  respectively  characterize  these 
two  classes  of  living  beings,  are  subordinate  to  this  one  leading  distinc- 
tion,— the  presence  of  a  Nervous  system,  and  of  its  peculiar  attributes 
in  the  one,^-and  its  absence  in  the  other.  Now  when  we  attempt  to 
analyze  those  peculiar  attributes,  we  may  resolve  them,  like  the  pro- 
perties of  the  material  body,  into  different  groups.  We  find  that  the 
first  excitement  of  all  mental  changes,  whether  these  involve  the  action 
of  the  feelings  or  of  the  reason,  depends  upon  sensations ;  which  are 
produced  by  impressions  made  upon  the  nerves  of  certain  parts  of  the 
body,  and  are  conveyed  by  these  to  a  particular  ganglionic  centre, 
which  is  termed  the  sensorium, — being  the  part  in  which  Sensation,  or 
the  capability  oi feeling  external  impressions,  especially  resides. 

845.  Now  there  are  numerous  actions,  especially  among  the  lower 
Animals,  which  seem  to  be  as  far  removed  from  the  influence  of  the 
Will,  and  as  little  directed  by  Intelligence,  as  the  Reflex  movements 
themselves;  but  which,  nevertheless,  depend  upon  sensation  for  their 
excitement.  The  sensation  may  immediately  direct  the  movement,  and 
may  call  the  muscular  apparatus  into  action  in  such  a  manner,  as,  with- 
out any  calculation  of  consequences,  any  intentional  adaptation  of  means 
to  ends,  any  exertion  of  the  reason,  or  any  employment  of  a  discrimi- 
nating Will,  to  produce  an  action,  or  train  of  actions,  as  directly  and 
obviously  adapted  to  the  well-being  of  the  individual,  as  we  have  seen 
those  of  the  reflex  character  to  be.  Of  this  we  have  an  excellent 
example  in  the  act  of  Sneezing ;  the  purpose  of  which  is  obviously  to 
expel  from  the  nasal  passages  those  irritating  matters,  the  sense  of 
whose  presence  excites  the  complicated  assemblage  of  muscular  move- 
ments concerned  in  the  operation.  This  class  of  actions  may  be  appro- 
priately termed  the  Consensual;  and  under  it  we  may  include  most  of 
those  purely  instinctive  actions  of  the  lower  animals,  which,  being 
prompted  by  sensations,  cannot  be  assigned  to  the  reflex  group.  These 
seem  to  make  up,  with  the  reflex,  nearly  the  whole  of  the  Animal 
functions  in  many  tribes ;  but  they  are  found  to  be  gradually  brought 
under  the  domination  of  the  Intelligence  and  Will,  as  we  rise  towards 
Man,  in  whom  those  faculties  are  most  strongly  developed,  so  as  to 
keep  the  Consensual  as  well  as  the  Reflex  actions  quite  in  subordination 
to  the  more  elevated  purposes  of  his  existence. — Closely  allied,  however, 
to  these,  are  the  purely  Emotional  movements  ;  in  which  the  sensation 
excites  a  mental  feeling  or  impulse,  that  reacts  upon  the  muscular 
system  without  giving  rise  to  any  distinct  idea,  and  consequently 
without  having  called  the  intellect  and  will  into  exercise.  In  fact, 
these  emotional  movements  are  often  performed  in  opposition  to  the 

•*  This  term,  derived  from  the  Greek  -{vxyi,  is  used  to  designate  the  sensorial  and 
mental  endowments  of  Animals,  in  the  most  comprehensive  acceptation  of  those  terms. 


478  OF  THE  NERVOUS   SYSTEM  AND   ITS   ACTIONS. 

strongest  efforts  of  the  will  to  restrain  them  ;  as  when  laughter  is 
provoked  by  some  ludicrous  sight  or  sound,  or  by  the  remembrance  of 
such,  at  an  unseasonable  time.  It  is  probable,  from  the  strong  mani- 
festations of  emotion  exhibited  by  many  of  the  lower  animals,  that 
some  of  the  actions  which  we  assemble  under  the  general  designation 
of  instinctive,  are  to  be  referred  to  this  group. 

846.  There  are  many  sensations,  however,  which  do  not  thus  imme- 
diately give  rise  to  muscular  movements ;  their  operation  being  rather 
that  of  stimulating  to  action  the  Intellectual  powers.  There  can  be 
little  doubt  that  all  Mental  processes  are  dependent,  in  the  first  instance, 
upon  Sensations,  which  serve  to  the  Mind  the  same  kind  of  purpose 
that  food  and  air  fulfil  in  the  economy  of  the  body.  If  we  could 
imagine  a  being  to  come  into  the  world  with  its  mental  faculties  fully 
prepared  for  action,  but  destitute  of  any  power  of  receiving  sensations, 
these  faculties  would  never  be  aroused  from  the  condition  in  which  they 
are  in  profound  sleep ;  and  the  being  must  remain  in  a  state  of  com- 
plete unconsciousness,  because  there  is  nothing  of  which  it  can  be  made 
conscious,  no  kind  of  idea  which  can  be  aroused  within  it.  But  after 
the  mind  has  once  been  in  active  operation,  the  destruction  of  all  future 
power  of  receiving  sensations  would  not  reduce  it  again  to  the  inactive 
condition.  For  sensations  are  so  stored  up  in  the  mind  by  the  power 
of  Memory,  that  they  may  give  rise  to  ideas  at  any  future  time ;  and 
thus  the  mind  may  feed,  as  it  were,  upon  the  past.  Now  the  ideas 
which  are  excited  by  sensations,  and  which  are  coloured  by  the  state  of 
Feeling  which  accompanies  them,  become  the  subjects  of  Reasoning 
processes .  more  or  less  complex,  sometimes  of  the  utmost  brevity  and 
simplicity,  sometimes  of  the  most  refined  and  intricate  nature.  These 
reasoning  processes,  when  they  result  in  a  determination  to  execute  a 
particular  movement,  execute  that  movement  by  an  act  of  Volition ; 
the  peculiar  character  of  which  is  that  it  is  the  expression  of  a  definite 
'purpose,  of  a  designed  adaptation  of  means  to  ends,  on  the  part  of  the 
individual  performing  it,  instead  of  being  the  result  of  the  mere  blind, 
indiscriminating  impulse  which  seems  to  be  the  mainspring  of  the 
instinctive  operations.  It  is  in  Man  that  we  find  the  highest  develop- 
ment of  the  reasoning  faculties  ;  but  it  is  quite  absurd  to  limit  them  to 
him,  as  some  have  done,  since  no  impartial  observer  can  doubt  that 
many  of  the  lower  animals  can  execute  reasoning  processes,  as  complete 
m  their  way  as  those  of  Man,  though  much  more  limited  in  their  scope. 

847.  Thus,  then,  w^e  have  to  consider  the  Nervous  system  under  four 
heads ; — first,  as  the  instrument  of  the  Reflex  actions  ; — second,  as  the 
instrument  of  the  Consensual  actions  ; — third,  as  the  instrument  of  the 
Emotional  actions ; — and  fourth,  as  the  instrument  of  the  Intellectual 
processes  and  of  Voluntary  movements.  There  is  reason  to  believe 
that  the  Nervous  Centre  from  which  the  muscles  derive  their  impulse  to 
contract,  is  the  same,  whether  the  movement  be  prompted  by  an  impres- 
sion which  does  not  excite  the  consciousness,  by  a  sensation,  by  an 
emotion,  or  by  a  volition;  and  that  this  instrument  may  be  played  upon, 
so  to  speak,  by  other  centres,  which  minister  to  these  functions  respec- 
tively. In  order  that  the  relations  of  the  component  parts  of  the 
Nervous  apparatus  may  be  better  understood,  it  will  be  desirable  to 


t 

m 


NERVOUS   SYSTEM   OF   EADIATA.  479 


take  a  brief  survey  of  its  comparative  structure  in  the  principal  groups 

of  Animals  ;  and  to  inquire  what  actions  may  be  justly  attributed  to  its 
veral  divisions  in  each  instance, — commencing  with  those  in  which 
e  structure  is  the  simplest,  and  the  variety  of  actions  the  smallesT; 
d  passing  on  gradually  to  those  in  which  the  structure  is  increased  in 

complexity  by  the  addition  of  new  and  distinct  parts,  and  in  which  the 

actions  present  a  corresponding  variety. 

2.    Comparative  Structure  and  Actions  qfthe  Nervous  System. 

848.  From  what  has  been  already  said  (§  373-9)  of  the  characters 
of  the  two  elementary  forms  of  the  Nervous  tissue,  it  is  evident  that  no 
Nervous  system  can  exist,  in  which  both  these  forms  should  not  be 
present.  We  look,  therefore,  for  ganglia,  composed  of  the  vesicular 
nervous  substance,  and  serving  as  the  centres  of  nervous  power ;  and 
for  cords  or  trunks,  composed  of  the  tubular  substance,  and  serving  to 
communicate  between  the  ganglia  and  the  parts  with  which  they  are  to 
be  functionally  connected.  Now  it  is  quite  certain  that,  at  present,  no 
such  Nervous  apparatus  can  be  detected  in  many  of  the  lowest  Animals  ; 
and  some  Physiologists  have  had  recourse  to  the  supposition  of  their 
possessing  a  "diffused"  nervous  system;  that  is,  of  their  possessing 
nervous  particles,  in  a  separate  form,  incorporated,  as  it  were,  with 
their  tissues.  But  we  have  seen  that  each  tissue  possesses  its  own  pro- 
perties, and  can  perform  its  own  actions  independently  of  the  rest ; — 
that  even  the  contractility  of  Muscular  fibre  is  by  no  means  dependent 
upon  the  Nervous  system,  though  usually  called  into  play  through  its 
means ; — and  that  the  simplest  office  of  a  Netvous  System  is  to  pro- 
duce a  muscular  movement  in  respondence  to  a  certain  impression  ; 
which  action  requires  that  it  should  have  an  internuncial  or  commu- 
nicating power,  only  to  be  exercised  (so  far  as  we  at  present  know)  by 
continuous  fibres.  The  apparent  absence  of  a  Nervous  system  is 
doubtless  to  be  attributed,  in  many  instances,  to  the  general  softness  of 
the  tissues  of  the  body,  which  prevents  it  from  being  clearly  made  out 
among  them.  And  it  is  to  be  remembered,  that,  on  the  principles 
already  stated,  we  should  expect  to  find  it  bearing  a  much  smaller 
proportion  to  the  entire  structure,  in  the  lowest  Animals,  whose 
functions  are  chiefly  Vegetative, — than  in  the  highest,  in  which  the 
vegetative  functions  seem  destined  merely  foi^  the  development  of 
the  Nervous  and  Muscular  systems,  and  for  the  sustenance  of  their 
powers. 

849.  Among  the  Radiated  classes,  the  parts  of  whose  bodies  are 
arranged  in  a  circular  manner  around  the  mouth,  and  repeat  each  other 
more  or  less  precisely,  the  Nervous  system  presents  a  corresponding 
form.  In  the  Star-fish,  for  example,  which  is  one  of  the  highest  of 
these  animals,  it  forms  a  ring,  which  surrounds  the  mouth ;  this  ring 
consists  of  nervous  cords,  which  form  communications  between  the 
several  ganglia,  one  of  which  is  placed  at  the  base  of  each  ray.  The 
number  of  these  ganglia  corresponds  with  that  of  the  rays  or  arms ; 
being  jive  in  the  common  Star-fish ;  and  from  nine  to  fifteen,  in  the 
species  possessing  those  several   numbers  of   members.     The  ganglia 


480  OF   THE   NERVOUS    SYSTEM   AND   ITS   ACTIONS. 

appear  to  be  all  similar  to  one  another  in  function,  as  they  are  in  the 
distribution  of  their  branches ;  every  one  of  them  sending  a  large  trunk 
along  its  own  ray,  and  two  small  filaments  to  the  organs  in  the  central 
disk.  The  rays  being  all  so  similar  in  structure,  as  to  be  exact  repeti- 
tions of  each  other,  it  would  appear  that  none  of  the  ganglia  can  have 
any  controlling  power  over  the  rest.  All  the  rays  (in  certain  species) 
have  at  their  extremities  what  seem  to  be  very  imperfect  eyes  ;  and  so 
far  as  these  can  aid  in  directing  the  movements  of  the  animal,  it  is  ob- 
vious that  they  will  do  so  towards  all  sides  alike.  Hence  there  is  no 
one  part,  which  corresponds  to  the  head  of  higher  animals ;  and  the 
ganglia  of  the  nervous  system,  like  the  parts  they  supply,  are  but  repe- 
titions of  one  another,  and  are  capable  of  acting  quite  independently. 
Each  would  perform  its  own  individual  functions  if  separated  from  the 
rest ;  but,  in  the  entire  animal,  their  actions  are  all  connected  with  each 
other  by  the  circular  cord,  which  passes  from  every  one  of  the  five  gan- 
glia to  those  on  either  side  of  it.  We  shall  find  that,  in  Articulated 
and  Vertebrated  animals,  there  is  a  similar  repetition  of  corresponding 
ganglia  on  the  two  sides  of  the  median  plane  of  the  body ;  and  that 
these  are  connected  by  transverse  bands,  analogous  in  function  to  the 
circular  cord  of  the  Star-fish.  Moreover,  we  shall  see  a  like  repetition 
of  ganglia,  almost  or  precisely  similar  in  function,  in  passing  from  one 
extremity  of  these  animals  to  the  other ;  and  these  ganglia  are  con- 
nected by  longitudinal  cords,  whose  function  is  in  like  manner  co7nmiS' 
sural. — From  the  best  judgment  we  can  form  of  the  actions  of  the  Star- 
fish, by  comparing  them  with  the  corresponding  actions  of  higher  ani- 
mals, we  may  fairly  regard  the  greater  number  of  them  as  simply  reflex  ; 
being  performed  in  direct  respondence  to  external  stimuli,  the  impres- 
sion made  by  which  is  propagated  to  one  or  more  of  the  ganglia,  and 
excites  in  them  a  motor  impulse.  How  far  the  movements  of  these 
animals  are  indicative  of  sensation^  we  have  not  the  power  of  deter- 
mining ;  but  it  may  be  safely  affirmed,  that  they  aflford  no  indication  of 
the  exercise  of  reasoning  faculties  or  of  voluntary  power. 

850.  Perhaps  the  simplest  form  of  a  Nervous  system  is  that  pre- 
sented by  certain  of  the  lower  Mollusca ;  for  the  body  not  here  pos- 
sessing any  repetition  of  similar  parts,  the  nervous  system  is  destitute 
of  that  multiplication  of  ganglia  which  we  see  in  the  Star-fish ;  whilst 
the  limited  nature  of  the  animal  powers  involves  a  corresponding  sim- 
plicity in  the  integral  parts  of  their  instrument.  The  animals,  to 
which  reference  is  here  made,  form  the  class  Tunicata,  which  is  inter- 
mediate, in  many  respects,  between  the  ordinary  Molluscs  and  the  Zoo- 
phytes. They  consist  essentially  of  an  external  membranous  bag  or 
tunic,  within  which  is  a  muscular  envelope,  and  again  within  this  a 
respiratory  sac,  which  may  be  considered  as  the  dilated  pharynx  of  the 
animal.  At  the  bottom  of  this  last,  is  the  entrance  to  the  stomach; 
which,  with  the  other  viscera,  lies  at  the  lower  end  of  the  muscular 
sac.  The  external  enveloped  have  two  orifices;  a  mouth,  to  admit 
water  into  the  pharyngeal  sac  ;  and  an  anal  orifice,  for  the  expulsion 
of  the  water  which  has  served  for  respiration,  and  of  that  which  has 
passed  through  the  alimentary  canal,  together  with  the  faecal  matter, 
the  ova,  &c.     A  current  of  water  is  continually  being  drawn  into  the 


I 


NERVOUS   SYSTEM   OF   MOLLUSCA.  481 

pharyngeal  sac,  by  the  action  of  the  cilia  that  line  it ;  and  of  this,  a 
part  is  driven  into  the  stomach,  conveying  to  it  the  necessary  supply 
of  aliment  in  a  very  finely-divided  state;  whilst  a  part  is  destined 
merely  for  the  aeration  of  the  circulating  fluid,  and  is  transmitted 
more  directly  to  the  anal  orifice,  after  having  served  that  purpose. 
These  animals  are  for  the  most  part  fixed  to  one  spot,  during  all  but 
the  earliest  period  of  their  existence ;  and  they  give  but  little  external 
manifestation  of  life,  beyond  the  continual  entrance  and  exit  of  the 
currents  already  adverted  to,  which,  being  efiected  by  ciliary  action,  is 
altogether  independent  of  the  nervous  system  (§  234).  When  any 
substance  is  drawn  in  by  the  current,  however,  the  entrance  of  which 
would  be  injurious,  it  excites  a  general  contraction  of  the  mantle  or 
muscular  envelope ;  and  this  causes  a  jet  of  water  to  issue  from  one  or 
both  orifices,  which  carries  the  ofiending  body  to  a  distance.  And, 
in  the  same  manner,  if  the  exterior  of  the  body  be  touched,  the 
mantle  suddenly  and  vij)lently  contracts,  and  expels  the  contents  of  the 
sac. 

851.  These  are  the  only  actions,  so  far  as  we  know,  which  the  Ner- 
vous system  of  these  animals  is  destined  to  perform.  They  do  not  ex- 
hibit the  least  trace  of  eyes,  or  of  other  organs  of  special  sense ;  and 
the  only  parts  that  appear  peculiarly  sensitive,  are  the  small  tentacula, 
or  feelers,  that  guard  the  oral  orifice.  Between  the  two  apertures  in 
the  mantle,  we  find  a  solitary  ganglion,  which  receives  branches  from 
both  orifices,  and  sends  others  over  the  muscular  sac.  This,  so  far  as 
we  know  at  present,  constitutes  the  whole  nervous  system  of  the  animal ; 
and  it  is  fully  sufficient  to  account  for  the  movements  which  have  been 
described.  For  the  impression  produced  by  the  contact  of  any  hard 
substance  with  the  tentacula,  or  with  the  general  surface  of  the  mantle, 
being  conveyed  by  the  afferent  fibres  of  this  ganglion,  will  excite  in  it 
a  reflex  motor  impulse ;  which,  being  transmitted  to  the  muscular  fibres 
of  the  contractile  sac,  as  well  as  to  those  circular  bands  that  surround 
the  orifices  and  act  as  sphincters^  will  produce  the  movements  in  ques- 
tion. 

852.  In  the  Conchifera,  or  Molluscs  inhabiting  bivalve  shells,  there 
are  invariably  two  ganglia,  having  difierent  functions.  The  larger  of 
these  (Plate  II.,  Fig.  1,  c\  corresponding  to  the  single  ganglion  of  the 
Tunicata,  is  situated  towards  the  posterior  end  of  the  body  (that  is,  the 
end  most  distant  from  the  mouth),  in  the  neighbourhood  of  the  posterior 
muscle  that  draws  the  valves  together ;  and  its  branches  are  distributed 
to  that  muscle,  to  the  mantle,  to  the  gills  (d,  d),  and  to  the  siphons  {e, 
e),  by  which  the  water  is  introduced  and  carried  off".  But  we  find 
another  ganglion,  or  rather  pair  of  ganglia  (a,  a),  situated  near  the 
front  of  the  body,  either  upon  the  oesophagus,  or  at  its  sides ;  these 
ganglia  are  connected  with  the  very  sensitive  tentacula  which  guard 
the  mouth ;  and  they  may  be  regarded  as  presenting  the  first  approach, 
both  in  position  and  functions,  to  the  brain  of  higher  animals.  In  the 
Oyster^  and  others  of  the  lower  Conchifera,  which  have  no  foot,  these 
are  the  only  principal  ganglia :  but  in  those  having  a  foot, — which  is  a 
muscular  tongue-like  organ, — we  find  an  additional  ganglion  {h)  con- 
nected with  it.     This  is  the  case  in  the  Solen,  or  animal  of  the  Razor- 

31 


482  OF   THE  NERVOUS  SYSTEM  AND   ITS   ACTIONS. 

shell ;  whose  foot  is  a  very  powerful  boring  instrument,  enabling  it  to 
penetrate  deeply  into  the  sand. — Here,  then,  we  have  three  distinct 
kinds  of  ganglionic  centres ;  every  one  of  which  may  be  doubled,  or 
repeated  on  the  two  sides  of  the  body.  First,  the  cephalic  ganglia,  a,  a, 
which  are  probably  the  sole  instruments  of  sensation  and  of  the  consen- 
sual movements ;  these  are  almost  invariably  double,  being  connected 
together  by  a  transverse  band,  which  arches  over  the  oesophagus.  Se- 
cond, the  pedal  ganglion,  h,  which  is  usually  single,  in  conformity  with 
the  single  character  of  the  organ  it  supplies ;  but  in  one  very  rare 
Bivalve  Mollusc,  the  foot  is  double,  and  the  pedal  ganglion  is  double 
also.  Third,  the  respiratory  ganglion,  c,  which  frequently  presents  a 
form  that  indicates  a  partial  division  into  two  halves,  corresponding 
with  the  repetition  of  the  organs  it  supplies  on  the  two  sides  of  the 
body.  Besides  these  principal  centres,  we  meet  with  numerous  smaller 
ones  upon  the  nervous  cords  (/,  f,  and  g,  g\  which  proceed  from  them 
to  the  diflferent  parts  of  the  general  muscular  envelope  or  mantle. 

853.  Now  it  will  be  observed,  that  the  two  cephalic  ganglia  a,  a,  are 
connected  with  the  pedal  ganglion,  h,  by  means  of  a  pair  of  trunks  pro- 
ceeding from  the  former  to  the  latter  ;  and  that  they  are,  in  like  man- 
ner, separately  connected  with  the  respiratory  or  branchial  ganglion,  c. 
There  is  good  reason  to  believe,  that  the  pedal  and  branchial  ganglia 
minister  to  the  purely  reflex  action  of  the  organs  they  respectively  sup- 
ply ;  and  that  they  would  serve  this  purpose  as  well,  if  altogether  cut  off 
from  connexion  with  the  cephalic  ganglia :  whilst  the  cephalic,  being  the 
instruments  of  the  actions  which  are  called  forth  by  sensation,  exert  a 
general  control  and  direction  over  the  movements  of  the  animal,  through 
the  medium  of  the  trunks  by  which  they  communicate  with  the  ganglia 
in  immediate  connexion  with  the  muscular  apparatus.  It  is  difficult, 
however,  to  make  satisfactory  experiments  upon  this  subject  in  these 
animals,  their  movements  being  for  the  most  part  slow  and  feeble,  and 
their  nervous  system  not  readily  accessible ;  and  our  idea  of  the  re- 
spective functions  of  their  ganglia  is  chiefly  founded  upon  the  distribu- 
tion of  their  nerves,  and  upon  the  analogous  operations  of  the  ganglia 
that  correspond  to  them  in  other  animals. 

854.  In  ascending  through  the  series  of  the  Mollusca,  we  find  the 
Nervous  system  increasing  in  complexity,  in  accordance  with  the  gene- 
ral organisation  of  the  body ;  the  addition  of  new  organs  of  special 
sensation,  and  of  new  parts  to  be  moved  by  muscles,  involving  the 
addition  of  new  ganglionic  centres,  whose  functions  are  respectively 
adapted  to  these  purposes.  But  we  find  no  other  multiplication  of 
similar  centres,  than  a  doubling  on  the  two  sides  of  the  body ;  excepting 
in  a  few  cases,  where  the  organs  they  supply  are  correspondingly  mul- 
tiplied. We  have  a  very  characteristic  example  of  this  in  the  arms  of 
the  Cuttle-fish,  which  are  furnished  with  great  numbers  of  contractile 
suckers,  every  one  possessing  a  ganglion  of  its  own.  Here  we  can  trace 
very  clearly  the  distinction  between  the  reflex  actions  of  each  individual 
sucker,  depending  upon  the  powers  of  its  own  ganglion  ;  and  the  move- 
ment prompted  by  sensation  which  results  from  its  connexion  with  the 
cephalic  ganglia.  ^  The  nervous  trunk,  which  proceeds  to  each  arm,  may 
be  distinctly  divided  into  two  tracts ;  in  one  of  which  are  contained 


I 


NERVOUS   SYSTEM   OF   MOLLUSCA.  483 

the  ganglia  which  peculiarly  appertain  to  the  suckers,  and  which  are 
connected  with  them  by  distinct  filaments ;  whilst  in  the  other  there  is 
nothing  but  fibrous  structure,  forming  a  direct  communication  between 
these  and  the  cephalic  ganglia ;  so  that  each  sucker  has  a  separate 
relation  with  a  ganglion  of  its  own,  whilst  all  are  alike  connected  with 
the  cephalic  ganglia,  and  are  placed  under  their  control.  We  see  the 
results  of  this  arrangement,  in  the  modes  in  which  the  contractile  power' 
of  the  suckers  may  be  called  into  operation.  When  the  animal  embraces 
any  substance  with  its  arm  (being  directed  to  this  action  by  its  sight  or 
other  sensation)  it  can  bring  all  the  suckers  simultaneously  to  bear  upon 
it ;  evidently  by  a  voluntary  or  instinctive  impulse  transmitted  along 
the  connecting  cords,  that  proceed  from  the  cephalic  ganglia  to  the 
ganglia  of  the  suckers.  On  the  other  hand,  any  individual  sucker  may 
be  made  to  contract  and  attach  itself,  by  placing  a  substance  in  con- 
tact with  it  alone ;  and  this  action  will  take  place  equally  well,  when 
the  arm  is  separated  from  the  body,  or  even  in  a  small  piece  of  the 
arm  .when  recently  severed  from  the  rest, — thus  proving  that,  when  it 
is  directly  excited  by  an  impression  made  upon  itself,  it  is  a  reflex  act, 
quite  independent  Of  the  cephalic  ganglia,  not  involving  sensation,  and 
taking  place  through  the  medium  of  its  own  ganglion  alone. 

855.  In  the  Molluscous  classes,  generally  speaking,  the  Nervous 
system  bears  but  a  small  proportion  to  the  whole  mass  of  the  body ; 
and  the  part  of  it  which  ministers  to  the  general  movements  of  the 
fabric,  is  often  small  in  proportion  to  those  which  serve  some  special 
purpose,  such  as  the  actions  of  respiration.  This  is  what  we  should 
expect  from  the  general  inertness  of  their  character,  and  from  the  small 
amount  of  muscular  structure  which  they  possess.  On  the  other  hand, 
in  the  Articulated  classes,  in  which  the  locomotive  apparatus  is  highly 
developed,  and  its  actions  of  the  most  energetic  kind,  we  find  the  Ner- 
vous system  almost  entirely  subservient  to  this  function.  In  its  usual 
form,  it  consists  of  a  chain  of  ganglia,  connected  by  a  double  cord  ; 
commencing  in  the  head,  and  passing  backwards  through  the  body  (Plate 
II.,  Fig.  2).  The  ganglia,  though  they  usually  appear  single,  are 
really  double ;  being  composed  of  two  equal  halves,  sometimes  closely 
united  on  the  median  line,  but  occasionally  remaining  separate,  like  the 
cephalic  ganglia  of  the  Solen  (Fig.  1,  a,  a),  and  being  united  together 
by  a  transverse  commissural  trunk.  In  like  manner,  the  longitudinal 
cord,  though  really  double  (as  seen  in  the  upper  part  of  Fig.  2),  often 
appears  to  be  single,  in  consequence  of  the  close  approximation  of  its 
lateral  halves  (as  in  the  lower  part  of  Fig.  2).  In  general  we  find  a 
ganglion  in  each  segment ;  giving  off  nerves  to  the  muscles  of  the  legs, 
as  in  Insects,  Centipedes,  &c. ;  or  to  the  muscles  that  move  the  rings  of 
the  body,  where  no  extremities  are  developed,  as  in  the  leech,  worm,  &c. 
In  the  lower  Vermiform  (or  worm-like)  tribes,  especially  in  the  marine 
species,  the  number  of  segments  is  frequently  very  great,  amounting 
even  to  several  hundreds ;  and  the  number  of  ganglia  follows  the  same 
proportion.  Whatever  be  their  degree  of  multiplication,  they  seem  but 
repetitions  of  one  another ;  the  functions  of  each  segment  being  the 
same  with  those  of  the  rest.  The  cephalic  ganglia,  however,  are  always 
larger  and  more  important ;  they  are  connected  with  the  organs  of 


484  OF   THE  NERVOUS   SYSTEM  AND   ITS  ACTIONS. 

special  sense ;  and  they  evidently  possess  a  power  of  directing  and  con- 
trolling the  movements  of  the  entire  body ;  whilst  the  power  of  each 
ganglion  of  the  trunk  is  confined  to  its  own  segment. — The  longitudinal 
ganglionic  cord  of  Articulata  occupies  a  position  which  seems  at  first 
sight  altogether  different  from  that  of  the  nervous  system  of  Yertebrated 
animals ;  being  found  in  the  neighbourhood  of  the  ventral  or  inferior 
surface  of  their  bodies;  instead  of  lying  just  beneath  their  dorsal  or 
upper  surface.  There  is  reason,  however,  for  regarding  the  whole  of 
the  body  of  these  animals  as  having  an  inverted  position ;  so  that  they 
may  be  considered  as  really  crkwling  upon  their  backs.  On  this  view, 
their  longitudinal  nervous  tract  corresponds  with  the  spinal  cord  of 
Vertebrata  in  position,  as  we  shall  find  that  it  does  in  function. 

856.  We  shall  draw  our  chief  illustrations  of  the  structure  of  the 
nervous  system  in  the  Articulated  series,  from  the  class  of  Insects  ;  in 
which  it  has  been  particularly  examined.  In  these  animals,  the  number 
of  segments  never  exceeds  twelve  (exclusive  of  the  head),  either  in  their 
larva,  pupa,  or  imago  states  ;  and  the  total  number  of  pairs  of  ganglia, 
therefore,  never  exceeds  thirteen,  including  the  cephalic  ganglia.  These, 
in  the  larva,  are  nearly  equal  in  size,  one  to  another  (Plate  II.,  Fig.  2, 
a,  and  1-12) ;  ^;he  functions  of  the  different  segments  of  the  body  being 
almost  uniform ;  and  the  development  of  the  organs  of  special  sense  not 
being  such,  as  to  involve  any  considerable  predominance  in  the  size  of 
the  cephalic  ganglia.  We  observe,  at  the  anterior  extremity,  the  pair 
of  cephalic  ganglia  {a) ;  from  which  proceeds,  on  each  side,  a  cord  of 
communication  to  the  first  ganglion  (1)  of  the  trunk.  This  double  cord, 
with  the  ganglia  above  and  below,  thus  forms  a  ring,  which  embraces 
the  oesophagus ;  the  cephalic  ganglia  being  situated  on  the  upper  side 
of  it,  whilst  the  ganglionic  column  of  the  trunk  lies  beneath  the  alimen- 
tary canal  along  its  whole  length.  In  the  SpJdnx  ligustri,  or  Privet 
Hawk-moth,  the  nervous  system  of  whose  larva  is  here  represented,  the 
last  two  segments  of  the  body  are  drawn  together,  as  it  were,  into  one ; 
and  instead  of  distinct  11th  and  12th  ganglia,  we  find  but  a  single  mass, 
nearly  double  the  size  of  the  rest,  and  obviously  formed  of  the  elements 
that  would  have  otherwise  gone  to  form  the  two. 

857.  When  the  structure  of  the  chain  of  ganglia  is  more  particularly 
inquired  into,  it  is  found  to  consist  of  two  distinct  tracts  ;  one  of  which 
is  composed  of  nervous  fibres  only,  and  passes  backwards  from  the 
cephalic  ganglia,  over  the  surface  of  all  the  ganglia  of  the  trunk; 
whilst  the  other  includes  the  ganglia  themselves.  Hence  every  part  of 
the  body  has  two  sets  of  nervous  connexions ;  a  direct  one  with  the 
ganglion  of  its  own  segment,  and  an  indirect  with  the  cephalic  ganglia. 
Impressions  made  upon  the  afferent  fibres,  which  proceed  from  any  part 
of  the  body  to  the  cephalic  ganglia,  become  sensations  when  conveyed 
to  the  latter ;  whilst,  in  respondence  to  these,  the  influence  of  sensa- 
tions received  by  the  cephalic  ganglia,  and  operating  through  them, 
harmonizes  and  directs  the  general  movements  of  the  body,  by  means 
of  the  communicating  cords  proceeding  from  them.  For  the  reflex 
operations,  on  the  other  hand,  the  ganglia  of  the  ventral  cord  are  suffi- 
cient ;  each  one  ministering  to  the  actions  of  its  own  segment,  and,  to 
a  certain  extent  also,  to  those  of  other  segments.     It  has  been  ascer- 


NERVOUS   SYSTEM   OF   ARTICULATA.  485 

tained  by  the  careful  dissections  of  Mr.  Newport,  that  of  the  fibres  con- 
stituting the  roots,  by  which  the  nerves  are  implanted  in  the  ganglia, 
some  pass  into  the  vesicular  matter  of  the  ganglion,  and,  after  coming 
into  relation  with  its  vesicular  substance,  pass  out  again  on  the  same 
side  (Fig.  152,  /,  k) ;  whilst  a  second  set,  after  traversing  the  vesicular 


Portion  of  the  ganglionic  tract  of  Pohjdesnius  maculatus  :—b,  inter-ganglionic  cord;  c,  anterior  net-res;  d, 
posterior  nerves ;  /,  k,  fibres  of  reflex  action ;  g,  h,  commissural  fibres ;  i,  longitudinal  fibres,  softened  and  en- 
larged, as  they  pass  through  ganglionic  matter. 

matter,  passes  out  by  the  trunks  proceeding  from  the  opposite  side  of 
the  same  ganglion ;  and  a  third  set  runs  along  the  portion  of  the  cord 
which  connects  the  ganglia  of  different  segments,  and  enters  the  ner- 
vous trunks  that  issue  from  them,  at  a  distance  of  one  or  more  ganglia 
above  or  below.  Thus  it  appears,  that  an  impression  conveyed  by  an 
afferent  fibre  to  any  ganglion,  may  excite  a  motion  in  the  muscles  of 
the  same  side  of  its  own  segment ;  or  in  those  of  the  opposite  side ;  or 
in  those  of  segments  at  a  greater  or  less  distance,  according  to  the 
point  at  which  the  efferent  fibres  leave  the  cord. 

858.  The  general  conformation  of  Articulated  animals,  arid  the 
arrangement  of  the  parts  of  their  nervous  system,  render  them  pecu- 
liarly favourable  subjects  for  the  study  of  the  reflex  actions ;  some  of 
the  principal  phenomena  of  which  will  now  be  described.  If  the  head 
of  a  Centipede  be  cut  off,  whilst  it  is  in  motion,  the  body  will  continue 
to  move  onwards  by  the  action  of  its  legs ;  and  the  same  will  take  place 
in  the  separate  parts,  if  the  body  be  divided  into  several  distinct  por- 
tions. After  these  actions  have  come  to  an  end,  they  may  be  excited 
again,  by  irritating  any  part  of  the  nervous  centres,  or  the  cut  extre- 
mity of  the  nervous  cord.  The  body  is  moved  forwards  by  the  regular 
and  successive  action  of  the  legs,  as  in  the  natural  state ;  but  its  move- 
ments are  always  forwards,  never  backwards,  and  are  only  directed  to 
one  side  when  the  forward  movement  is  checked  by  an  interposed  ob- 
stacle. Hence,  although  they  might  seem  to  indicate  consciousness 
and  a  guiding  will,  they  do  not  so  in  reality ;  for  they  are  carried  on, 
as  it  were,  mechanically ;  and  show  no  direction  of  object,  no  avoidance 
of  danger.  If  the  body  be  opposed  in  its  progress  by  an  obstacle  of 
not  more  than  half  of  its  own  height,  it  mounts  over  it,  and  moves  directly 
onwards,  as  in  its  natural  state ;  but  if  the  obstacle  be  equal  to  its  own 
height,  its  progress  is  arrested,  and  the  cut  extremity  of  the  body  re- 


486  OF  THE  NERVOUS   StSTBM  AND  ITS  ACTIONS. 

mains  forced  up  against  the  opposing  substance,  the  legs  still  continuing 
to  move. — If,  again,  the  nervous  cord  of  a  Centipede  be  divided  in  the 
middle  of  the  trunk,  so  that  the  hinder  legs  are  cut  off  from  connexion 
with  the. cephalic  ganglia,  they  will  continue  to  move,  but  not  in'  har- 
mony with  those  of  the  fore  part  of  the  body ;  being  completely  para- 
lysed, as  far  as  the  animal's  controlling  power  is  concerned ;  though 
sdll  capable  of  performing  reflex  movements,  by  the  influence  of  their 
own  ganglia,  which  may  thus  continue  to  propel  the  body,  in  opposition 
to  the  determinations  of  the  animal  itself. — The  case  is  still  more  re- 
markable, when  the  nervous  cord  is  not  merely  divided,  but  a  portion 
of  it  is  entirely  removed  from  the  middle  of  the  trunk ;  for  the  anterior 
legs  still  remain  obedient  'to  the  animal's  control ;  the  legs  of  the  seg- 
ments from  which  the  nervous  cord  has  been  removed,  are  altogether 
motionless ;  whilst  those  of  the  posterior  segments  continue  to  act, 
through  the  reflex  powers  of  their  own  ganglia,  in  a  manner  which 
shows  that  the  animal  has  no  power  of  checking  or  directing  them. 

859.  The  stimulus  to  the  reflex  movements  of  the  legs,  in  the  fore- 
going cases,  appears  to  be  given  by  the  contact  of  the  extremities  with 
the  solid  surface  on  which  they  rest.  In  other  cases,  the  appropriate 
impression  can  only  be  made  by  the  contact  of  liquid ;  thus  a  Dytiscus 
(a  kind  of  water-beetle)  having  had  its  cephalic  ganglia  removed,  re- 
mained motionless,  so  long  as  it  rested  upon  a  dry  surface ;  but  when 
cast  into  water,  it  executed  the  usual  swimming  motions  with  great 
energy  and  rapidity,  striking  all  its  comrades  to  one  side  by  its  vio- 
lence, and  persisting  in  these  for  more  than  half  an  hour.  Other 
movements,  again,  may  be  excited  through  the  respiratory  surface. 
Thus,  if  the  head  of  a  Centipede  be  cut  off,  and,  while  it  remains  at 
rest,  some  irritating  vapour  (such  as  that  of  ammonia  or  muriatic  acid) 
be  caused  to  enter  the  air-tubes  on  one  side  of  the  trunk,  the  body  will 
be  immediately  bent  in  the  opposite  direction,  so  as  to  withdraw  itself 
as  much  as  possible  from  the  influence  of  the  vapour ;  if  the  same  irri- 
tation be  then  applied  on  the  other  side,  the  reverse  movement  will 
take  place ;  and  the  body  may  be  caused  to  bend  in  two  or  three  diffe- 
rent curves,  by  bringing  the  irritating  vapour  into  the  neighbourhood 
of  different  parts  of  either  side.  This  movement  is  evidently  a  reflex 
one,  and  serves  to  withdraw  the  entrances  of  the  air-tubes  from  the 
source  of  irritation ;  in  the  same  manner  as  the  acts  of  coughing  and 
sneezing  in  the  higher  animals  cause  the  expulsion,  from  their  air-pas- 
sages, of  solid,  liquid,  or  gaseous  irritating  matters,  which  may  have 
found  their  way  into  them. 

860.  From  these  and  similar  facts  it  appears,  that  the  ordinary 
movements  of  the  legs  and  wings  of  Articulated  animals  are  of  a  reflex 
nature,  and  may  be  effected  solely  through  the  ganglia  with  which 
these  organs  are  severally  connected ;  whilst  in  the  perfect  being,  they 
are  harmonized,  controlled,  and  directed  by  the  instinctive  guidance, 
which  depends  upon  sensations  acting  through  the  cephalic  ganglia  and 
the  fibres  proceeding  from  them.  There  is  strong  reason  to  believe, 
that  the  operations  to  which  these  ganglia  are  subservient,  are  almost 
entirely  of  a  consensual  nature  ;  being  immediately  prompted  by  sensa- 
tions, chiefly  those  of  sight,  and  seldom  involving  any  processes  of  a 


REFLEX  AND  CONSENSUAL  ACTIONS  OF  INSECTS.       487 

truly  rational  character.  When  we  attentively  consider  the  hahits  of 
these  animals,  we  find  that  their  actions,  though  evidently  directed  to 
the  attainment  of  certain  ends,  are  very  far  from  being  of  the  same 
spontaneous  nature,  or  from  possessing  the  same  designed  adaptation 
of  means  to  ends,  as  those  performed  by  ourselves,  or  by  the  more  in- 
telligent Vertebrata,  under  like  circumstances.  We  judge  of  this  by 
their  unvarying  character,  the  difierent  individuals  of  the  same  species 
executing  precisely  the  same  movements  when  the  circumstances  are 
the  same ;  and  by  the  very  elaborate  nature  of  the  mental  operations 
which  would  be  required,  in  many  instances,  to  arrive  at  the  same 
results  by  an  efi'ort  of  reason.  Of  such  we  cannot  have  a  more  remark- 
able example,  than  is  to  be  found  in  the  operations  of  Bees,  Wasps, 
and  other  social  Insects ;  which  construct  habitations  for  themselves, 
upon  a  plan  which  the  most  enlightened  human  intelligence,  working 
according  to  the  most  refined  geometrical  principles,  could  not  surpass ; 
but  which  yet  do  so  without  education  communicated  by  their  parents, 
or  progressive  attempts  of  their  own,  and  with  no  trace  of  hesitation, 
confusion,  or  interruption, — the  difi'erent  individuals  of  a  community  all 
labouring  efi"ectively  for  one  common  purpose,  because  their  instinctive 
or  consensual  impulses  are  the  same. 

861.  It  is  interesting  to  remark  that,  in  the  change  from  the  Larva 
to  the  perfect  or  Im.ago  state  of  the  Insect,  the  Cephalic  ganglia 
undergo  a  great  increase  in  size.  (Plate  II.,  Fig.  3,  a,  a,)  This 
evidently  has  reference  to  the  increased  development  of  the  organs  of 
special  sense  in  the  latter;  the  eyes  being  much  more  perfectly 
formed ;  antennae  and  other  appendages  used  for  feeling  being  evolved ; 
and  rudimentary  organs  of  hearing  and  smell  being  added.  In 
respondence  to  the  new  sensations,  which  the  animal  must  thus 
acquire,  a  great  number  of  new  instinctive  actions  are  manifested; 
indeed  it  may  be  said,  that  the  instincts  of  the  perfect  Insect  have 
frequently  nothing  in  common  with  those  of  the  Larva.  The  latter 
have  reference  to  the  acquirement  of  food ;  the  former  chiefly  relate 
to  the  acts  of  reproduction,  and  to  the  provisions  requisite  for  the  de- 
posit and  protection  of  the  eggs  and  the  early  nutrition  of  the  young. 
— We  find  another  important  change  in  the  nervous  system  of  the 
adult  or  perfect  Insect ;  namely,  the  concentration  of  the  ganglionic 
matter  of  the  ventral  cord  in  the  thoracic  region  (g,  /) ;  with  the  three 
segments  of  which,  the  three  pairs  of  legs  and  the  two  pairs  of  wings 
are  connected.  The  nine  segments  of  the  4bdomen,  in  the  perfect 
Insect,  give  attachment  to  no  organs  of  motion,  and  are  seldom  them- 
selves very  moveable ;  and  we  find  that  the  ganglia  which  correspond 
with  them  have  undergone  no  increase  in  size,  but  have  rather  dimi- 
nished, and  have  sometimes  almost  completely  disappeared.  Where 
the  last  segment,  however,  is  furnished  with  a  particularly  moveable 
appendage,  such  as  a  sting,  or  an  ovipositor,  we  always  find  a  large 
ganglion  in  connexion  with  it. 

862.  These  ganglia  of  the  ventral  cord  evidently  correspond  in 
function  with  the  'pedal  ganglion  of  the  Mollusca;  being  so  many 
repetitions  of  it ;  in  accordance  with  the  number  of  members.  We 
have  now  to  speak  of  a  system  of  respiratory  ganglia,  which  also  are 


488  OF  THE   NERVOUS  SYSTEM  AND   ITS   ACTIONS. 

repeated  in  like  manner,  in  accordance  with  the  condition  of  the 
respiratory  apparatus ;  this  being  dififused  through  the  whole  body,  in 
most  of  the  Articulata,  instead  of  being  restricted  to  one  spot  as  in  the 
Mollusca.  The  system  of  respiratory  nerves  consists  of  a  chain  of 
minute  ganglia,  lying  upon  the  larger  cord,  and  sending  off  its  delicate 
nerves  between  those  that  proceed  from  the  ganglia  of  the  latter,  as 
seen  in  Fig.  2.  These  respiratory  ganglia  and  their  nerves  are  best 
seen  in  the  thoracic  portion  of  the  cord,  where  the  cords  of  communica- 
tion between  the  pedal  ganglia  diverge  or  separate  from  one  another. 
And  this  is  particularly  the  case  in  the  Pupa  state,  when  the  whole 
cord  is  being  shortened,  and  their  divergence  is  increased.  The  tho- 
racic portion  of  the  cord,  in  the  Pupa  of  the  Sphinx  ligustri,  is  shown 
in  Plate  II.,  Fig.  4 ;  where  «,  6,  and  c,  represent  the  2d,  3d,  and  4th 
double  ganglia  of  the  ventral  cord;  c?,  d^  the  cords  of  connexion 
between  them,  here  widely  diverging  laterally;  and  g,  e,  the  small 
respiratory  ganglia,  which  are  connected  with  each  other  by  delicate 
filaments  that  pass  over  the  ganglia  of  the  ventral  cord,  and  which  send 
off  lateral  branches,  that  are  distributed  to  the  air-tubes  and  other  parts 
of  the  respiratory  apparatus,  and  communicate  with  those  of  the  other 
system. 

863.  Besides  the  respiratory  system  of  ganglia  and  nerves,  there  is 
in  Insects,  as  in  some  Molluscs,  a  set  of  minute  ganglia,  which  is  espe- 
cially connected  with  the  acts  of  mastication  and  swallowing,  its  fila- 
ments being  distributed  to  the  muscles  of  the  mouth  and  pharynx,  and 
some  of  its  ganglia  being  even  found  on  the  stomach,  where  that  organ 
is  remarkable  for  its  muscular  powers.  The  number  and  arrangement 
of  these  ganglia  vary  considerably  in  different  animals,  even  in  those 
of  the  same  group :  but  some  traces  of  this  distinct  system,  which  is 
designated  as  the  stomato-gastrie,  may  always  be  found.  One  of  the 
minute  ganglia  appertaining  to  it,  and  forming  its  anterior  termination, 
is  seen  to  lie  on  the  median  line,  in  front  of  the  great  cephalic  ganglia, 
in  Plate  II.,  Fig.  3,  c.  From  this  a  trunk  passes  backwards  along  the 
oesophagus ;  which  may  be  likened  to  the  oesophageal  branches  of  the 
Par  vagum  in  Yertebrata.  Two  other  small  ganglia  communicating 
with  this,  are  seen  at  d,  d. 

864.  We  are  not  without  traces,  moreover,  among  Invertebrated 
animals,  of  the  Sympathetic  system  of  the  higher  classes ;  though  it  is 
quite  a  mistake  to  compare  the  entire  system  of  nerves  and  ganglia  in 
the  former,  with  the  Sympathetic  system  of  the  latter,  as  was  formerly 
done.  The  chief  distribution  of  the  branches  of  the  Sympathetic  of 
Vertebrata  is  upon  the  walls  of  the  blood-vessels,  and  upon  the  muscular 
substance  of  the  heart  and  alimentary  canal ;  and  it  is  by  the  passage 
of  ^  some  of  the  filaments,  from  the  system  of  minute  ganglia  just 
pointed  out,  to  the  dorsal  vessel,  that  we  recognise  it  as  combining  the 
functions  of  the  Sympathetic  with  those  of  the  gastric  and  cardiac  por- 
tions of  the  Par  vagum.  It  will  be  remembered  that  there  is  a  frequent 
inosculation  between  these  two  nerves,  even  in  the  highest  animals. 

865.  Thus  we  have  seen  that,  in  Invertebrated  animals,  the  Nervous 
System  consists  of  a  series  of  isolated  ganglia,  connected  together  by 
fibrous  trunks.     The  number  of  these  ganglia,  and  the  variety  of  their 


NERVOUS   SYSTEM   OF   INVERTEBRATA.  489 

function,  entirely  depend  upon  the  number  and  variety  of  the  organs  to 
be  supplied.  In  the  lowest  Mollusca,  the  regulation  of  the  ingress  and 
egress  of  water  seems  almost  the  only  function  to  be  performed ;  and 
here  we  have  but  a  single  ganglion.  In  the  Star-fish,  we  have  five  or 
more  ganglia ;  but  they  are  all  repetitions  one  of  another,  and  are  ob- 
viously the  centres  of  action  to  the  several  segments  to  which  they 
respectively  belong,  neither  having  a  predominance  over  the  rest.  And 
in  the  higher  Mollusca,  and  in  Articulata,  we  have  a  ganglion,  or  more 
commonly  a  pair  of  ganglia,  situated  at  the  anterior  extremity  of  the 
body,  connected  with  the  organs  of  special  sensation,  and  evidently  ex- 
erting a  dominant  influence  over  the  rest.  In  the  lower  Mollusca,  we 
have  but  a  single  ganglion  for  general  locomotion ;  but  this  is  doubled 
laterally,  and  repeated  longitudinally  in  ijie  Articulata,  in  accordance 
with  the  multiplication  of  their  locomotive  organs,  so  as  to  form  the 
ventral  cord.  In  like  manner,  the  Mollusca  possess  a  single  ganglionic 
centre  for  the  respiratory  movements;  and  this  is  repeated  in  every 
segment  of  the  Articulata,  forming  a  chain  of  respiratory  ganglia,  which 
regulates  the  actions  of  the  extensively-difiused  respiratory  apparatus  of 
these  animals.  The  acts  of  mastication  and  deglutition,  again,  in  both 
sub-kingdoms,  are  immediately  dependent  upon  a  distinct  set  of  gan- 
glionic centres ;  which  are  connected,  however,  like  the  preceding,  with 
the  cephalic  ganglia.  And  we  have  further  seen,  that,  wherever  special 
organs  are  developed,  whose  operations  depend  upon  muscular  contrac- 
tion, ganglionic  centres  are  developed  in  immediate  relation  with  them ; 
so  as  to  enable  them  to  act  by  their  simple  reflex  power,  as  well  as 
under  the  direction  of  the  cephalic  ganglia ;  as  in  the  case  of  the  suckers 
of  the  Cuttle-fish. — Now  when  we  inquire  into  the  relation  of  the 
cephalic  ganglia  of  Invertebrata  with  the  Brain  of  the  higher  Verte- 
brated  animals,  we  find  that  these  organs  cannot  be  compared  in  their 
totality ;  for  that  the  former  are  the  representatives  of  a  certain  portion 
only,  and  that  usually  but  a  small  one,  of  the  latter.  The  cephalic 
ganglia  of  the  Centipede,  for  example,  receive  nerve-trunks  from  the 
eyes,  the  antennae,  and  other  sensory  organs,  and  give  off"  motor  nerves 
to  the  diff'erent  moveable  parts  of  the  head ;  and  the  history  of  their 
development,  which  has  been  studied  by  Mr.  Newport,  shows  that  they 
may  be  considered  as  the  coalesced  ganglia  of  the  four  segments  of 
which  the  anterior  part  of  the  head  is  composed ;  whilst  the  first  sub- 
oesophageal  ganglia  are  formed  by  the  coalescence  of  the  four  segments 
entering  into  the  composition  of  the  posterior  part  of  the  head.  The 
increased  bulk  of  the  cephalic  ganglia  in  the  higher  Articulata,  and 
especially  in  the  perfect  Insect,  is  obviously  for  the  most  part  dependent 
upon  the  increased  development  of  the  visual  apparatus,  for  we  find  it 
everywhere  proportional  to  it ;  and  thus  we  may  look  upon  them  as 
mainly  optic  ganglia,  serving  to  direct  the  actions  of  the  animal  through 
the  sense  of  sight. — There  is  no  part  of  these  organs  which  can  be  con- 
sidered as  superadded  to  the  ganglionic  masses  which  are  the  immediate 
centres  of  the  cephalic  nerves ;  consequently  there  is  nothing  which 
can  be  likened  either  to  the  Cerebrum  or  to  the  Cerebellum  of  Verte- 
brata.  And  the  representative  of  these  cephalic  ganglia  in  the  Verte- 
brated  Encephalon,  is  that  series  of  ganglionic  centres  at  the  base  of 


490  OF   THE  NERVOUS   SYSTEM   AND   ITS  ACTIONS. 

the  brain,  which  constitute  (as  we  shall  presently  find)  its  fundamental 
portion,  and  with  which  all  the  cephalic  nerves  are  immediately  con- 
nected. 

866.  When  we  direct  our  attention  to  the  nervous  system  of  the 
Vertebrated  series,  we  perceive  that  it  differs  from  that  of  the  Inver- 
tebrated  classes  we  have  been  considering,  in  two  remarkable  features. 
In  these  last,  it  has  seemed  but  as  a  mere  appendage  to  the  rest  of 
the  system,  designed  to  bring  its  several  parts  into  more  advantageous 
relation.  On  the  other  hand,  in  the  Vertebrata,  the  whole  structure 
appears  subservient  to  it,  and  designed  but  to  carry  its  purposes  into 
operation. — Again,  in  the  Invertebrata,  we  do  not  find  any  special 
adaptation  of  the  organs  of  support  for  the  protection  of  the  Nervous 
System ;  for  it  is  either  enclosed,  with  the  other  soft  parts  of  the  body, 
in  one  general  hard  tegument,  as  in  the  Star-fish  and  other  Echinoder- 
mata,  and  in  Insects,  Crustacea,  and  other  Articulata ;  or  it  receives  a 
still  more  imperfect  protection,  or  even  none  at  all,  as  in  the  Mollusca. 
Now  in  the  Vertebrata,  we  find  a  special  and  complex  bony  apparatus, 
adapted  in  the  most  .perfect  manner  for  the  protection  of  the  Nervous 
system ;  and  it  is,  in  fact,  the  possession  of  a  jointed  spinal  column, 
and  of  its  cranial  expansion,  which  best  characterizes  the  group. 

867.  The  Nervous  System  of  Vertebrata  is  not  merely  remarkable 
for  its  high  development,  relatively  to  the  remainder  of  the  structure  : 
it  is  also  distinguished  by  the  possession  of  parts,  to  which  we  have 
nothing  analogous  in  the  lower  tribes  ;  and  by  the  mode  in  which  these 
are  concentrated  and  combined,  so  as  to  form  one  continuous  mass, 
instead  of  consisting  of  a  series  of  scattered  ganglia. — The  chief  parts 
which  are  newly  introduced  (so  to  speak)  in  this  sub-kingdom,  are  the 
Cerebral  Hemispheres  and  Cerebellum ;  of  which  there  are  no  traces 
whatever  in  the  lower  Articulata  and  Mollusca,  and  but  very  uncertain 
representations  in  the  highest.  These  are  superimposed,  as  it  were, 
upon  the  cephalic  ganglia  connected  with  the  organs  of  special  sense, 
and  upon  the  cords  that  connect  them  with  the  first  ganglion  of  the 
trunk. — Again,  we  find  that  the  locomotive  ganglia,  which  formed  the 
long  knotted  cord  of  the  Articulata,  are  united  with  the  centres  of  the 
respiratory  system,  and  with  those  of  the  stomato-gastric  system,  to 
form  one  continuous  tract,  which  commences  anteriorly  from  the  gan- 
glia of  special  sense,  and  runs  backwards*  without  interruption,  in  the 
canal  of  the  Vertebral  column,  forming  the  spinal  cord.  This  is  a  con- 
tinuous instead  of  an  interrupted  ganglionic  mass ;  it  is  composed  of 
two  lateral  halves,  precisely  similar  to  each  other ;  and  each  of  these 
consists  of  two  parts,  as  distinct  from  each  other  as  the  two  tracts  in 
the  ventral  cord  of  the  Articulata, — namely,  a  fibrous  structure,  which 
connects  every  part  of  it  with  the  Encephalon  (or  collection  of  nervous 
masses  within  the  cranium),  and  which  also  serves  to  connect  together 
the  different  parts  of  the  cord  itself, — and  a  vesicular  portion,  which 
forms  the  proper  centre  of  the  greater  part,  if  not  the  whole,  of  the 
fibres  entering  into  the  roots  of  those  nerves.  The  anterior  portion  of 
the  Spinal  cord,  which  is  prolonged  into  the  cranium,  and  comes  into 

*  When  we  speak  of  the  Vertebrata  generally,  their  bodies  are  of  course  supposed  to 
be  in  a  horizontal  position, — not  vertical,  as  in  Man. 


I 

NERVOUS   SYSTEM   OF   VERTEBRATA.  491 

immediate  relation  with  the  Encephalon,  is  termed  the  Medulla  Oblon- 
gata. It  is  in  this,  that  the  centres  of  the  respiratory  and  stomato- 
gastric  nerves  are  found ;  the  situation  of  these  important  ganglia  within 
the  cranium,  being  obviously  destined  to  protect  them  from  those  inju- 
ries, to  which  the  Spinal  Cord  itself  is  liable.  '     ~ 

868.  Thus,  then,  we  are  led  to  recognise  in  the  Nervous  system  of 
Vertebrata  the  following  fundamental  parts. — 1.  A  system  of  ganglia 
subservient  to  the  reflex  actions  of  the  organs  of  locomotion,  and  cor- 
responding with  the  chain  of  pedal  or  locomotive  ganglia  that  makes 
up  the  chief  part  of  the  ventral  cord  of  the  Articulata ;  in  this  system, 
the  gray  or  vesicular  matter  forms  one  continuous  tract,  which  occupies 
the  interior  of  the  Spinal  Cord. — 2.  A  ganglionic  centre  for  the  move- 
ments of  respiration,  and  another  for  those  of  mastication  and  degluti- 
tion ;  these,  with  part  of  the  preceding,  make  up  the  proper  substance 
of  the  Medulla  Oblongata. — 3.  A  series  of  ganglia,  in  immediate  con- 
nexion with  the  organs  of  Special  Sense  ;  these  are  situated  within  the 
cranium,  at  the  anterior  extremity  of  the  Medulla  Oblongata ;  and,  in 
the  lowest  Vertebrata,  they  constitute  by  far  the  largest  portion  of  the 
entire  Encephalon. — 4.  The  Cerebellum,  which  is  a  sort  of  off-shoot 
from  the  upper  extremity  of  the  Medulla  Oblongata,  lying  behind  the 
preceding. — 5.  The  Cerebral  Hemispheres,  a  pair  of  ganglionic  masses, 
which  lie  upon  the  ganglia  of  special  sense,  capping  them  over  more 
or  less  completely,  according  to  their  relative  development. — These  last 
two  organs  exist  in  the  lowest  Vertebrata,  as  in  Invertebrated  animals 
generally,  in  quite  a  rudimentary  state ;  but  their  development,  rela- 
tively to  other  parts  of  the  Encephalon,  and  to  the  entire  bulk  of  the 
animal,  increases  as  we  ascend  the  scale ;  so  that  in  Man  and  the  higher 
Mammalia  they  constitute  by  far  the  largest  portion  of  the  Nervous 
centres,  and  are  essential  to  the  greater  part  of  the  operations  of  the 
Nervous  system.  The  development  of  the  Cerebral  Hemispheres  holds 
a  close  relation  with  the  increase  of  the  Intelligence,  and  with  the  pre- 
dominance of  the  Will  over  the  involuntary  impulses.  The  increased 
size  of  the  Cerebellum,  on  the  other  hand,  seems  connected  with  the 
necessity  which  exists,  for  the  adjustment  and  combination  of  the  loco- 
motive powers,  when  the  variety  in  the  movements  performed  by  the 
animal  is  great,  and  a  more  perfect  harmony  is  required  among  them. 
— A  sketch  of  the  mode  in  which  these  different  parts  are  combined 
and  arranged  in  the  several  classes  of  Vertebrata,  and  of  their  relative 
development  in  each,  will  aid  us  in  the  subsequent  more  detailed  exami- 
nation of  their  functions. 

869.  In  the  class  of  Fishes,  taken  as  a  whole,  the  Encephalon  bears 
a  much  smaller  proportion  to  the  Spinal  Cord,  than  in  the  higher  Ver- 
tebrata. In  the  curious  Amphioxus,  or  Lancelot,  there  is  no  discover- 
able nervous  mass  anterior  to  the  Medulla  Oblongata;  and  we  have  here, 
therefore,  an  animal  regularly  formed  upon  the  plan  which  occasionally 
presents  itself  as  a  monstrosity  in  Man, — namely,  having  the  Spinal 
Cord  and  Medulla  Oblongata  for  the  whole  of  the  nervous  centres,  and 
being  anencephalous,  or  destitute  of  any  proper  encephalon.  In  some 
of  the  lowest  Vermiform  (worm-like)  Fishes,  such  as  the  Lamprey,  the 
cephalic  masses  are  very  little  more  developed  in  proportion  to  the 


492  OF   THE   NERVOUS   SYSTEM   AND   ITS   ACTIONS. 

Spinal  Cord,  than  are  the  cephalic  ganglia  of  Insects  in  reference  to 
their  chain  of  ventral  ganglia.  But  as  the  organs  of  special  sense  ac- 
quire a  more  complete  evolution,  we  find  the  ganglia  connected  with 
them  presenting  a  greatly-increased  size.  On  opening  the  cranial 
cavity  of  a  Fish,  we  usually  observe  four  nervous  masses  (three  of  them 
in  pairs)  lying,  one  in  front  of  the  other,  nearly  in  the  same  line  with 
the  Spinal  cord.  The  first  or  most  anterior  of  these  are  the  Olfactory 
ganglia  (Plate  II.,  Figs.  §,  6,  7,  a),  or  the  ganglia  of  the  nerves  of 
smell;  the  nature  of  which  is  known,  from  their  being  situated  at  the 
origin  of  the  Olfactory  nerves.  In  the  shark  and  some  other  Fishes, 
these  are  separated  from  the  rest  by  peduncles  or  foot-stalks  ;  a  fact 
of  much  interest,  as  explaining  the  arrangement  which  we  find  in  Man. 
What  is  commonly  termed  the  trunk  of  his  Olfactive  nerve  is  really  the 
commissure  connecting  the  Olfactive  ganglion  (known  as  the  bulbous 
enlargement  that  lies  upon  the  cribriform  plate  of  the  Ethmoid  bone) 
"with  the  other  portions  of  his  Encephalon  :  the  proper  fibres  of  the 
nerve  being  those  which  come  ofi"  from  this  ganglion,  in  the  numerous 
branches  that  proceed  from  it  into  the  nasal  cavity. — Behind  the  Olfac- 
tive ganglia  is  a  pair  of  masses,  6,  h,  of  which  the  relative  size  varies 
greatly  in  different  Fishes.  Thus  in  the  Perch,  whose  Encephalon  is 
here  figured,  their  size  is  intermediate  between  that  of  the  first  and 
third  pairs ;  being  as  much  inferior  to  that  of  the  third,  as  it  is  superior 
to  that  of  the  first.  On  the  other  hand,  in  the  Shark  and  several  other 
Fishes,  they  are  considerably  larger  than  the  succeeding  pair.  These 
second  ganglia  are  commonly  considered  as  the  rudiments  of  the  Cere- 
bral Hemispheres  ;  but  there  seems  reason  for  regarding  them  as  being 
chiefly  the  representatives  of  the  Corpora  Striata ;  the  existence  of  a 
cerebrum  being  only  indicated  by  a  thin  layer  of  vesicular  matter, 
which  overlies  the  ventricle  that  is  found  in  these  bodies  in  the  brains 
of  Cartilaginous  Fishes  alone. — Behind  them,  and  forming  the  third 
pair  of  ganglionic  masses,  c,  c?,  are  two  large  bodies,  from  which  the 
optic  nerves  arise ;  these  evidently  represent  the  Optic  ganglia,  which 
constitute  the  principal  mass  of  the  cephalic  ganglia  in  Insects  and  the 
higher  Mollusca,  and  with  which  the  Corpora  Quadrigemina  of  higher 
Vertebrata  partly  correspond;  but  they  probably  represent  also  the 
Thalami  Optici  of  the  brain  of  Man  and  the  higher  animals. — At  the 
back  of  these,  overlying  the  top  of  the  spinal  cord,  is  a  single  mass,  d^ 
the  Cerebellum.  This,  also,  varies  greatly  in  its  relative  dimensions, 
being^  much  more  highly  developed  in  the  active  and  rapacious  Sharks, 
than  it  is  in  Fishes  of  inferior  muscular  energy  and  variety  of  move- 
ment.—-The  Spinal  Cord  e^  is  divided  at  the  top  by  a  fissure,  which  is 
most  wide  and  deep  beneath  the  cerebellum,  where  there  is  a  complete 
separation  between  its  two  halves.  This  opening  corresponds  to  that, 
through  which  the  oesophagus  passes  in  the  Invertebrata ;  but  as  the 
entire  nervous  mass  of  Vertebrated  animals  lies  above  the  alimentary 
canal  (or  nearer  the  dorsal  surface),  it  does  not  serve  the  same  purpose 
in  them ;  and  in  the  higher  classes,  the  fissure  is  almost  entirely  closed 
by  the  union  of  the  two  halves  on  the  median  plane,  the  fourth  ven- 
tricle, however,  being  a  remnant  of  it.  This  cavity  is  partly  seen  in 
Fig.  7,  which  is  a  vertical  section  of  the  brain  whose  upper  and  under 


NERVOUS   CENTRES   OF   REPTILES.  493 

surfaces  are  shown  in  Figs.  5  and  6. — In  the  lateral  strands  of  the 
Medulla  Oblongata,  close  to  the  fourth  ventricle,  there  is  a  pair  of 
ganglionic  centres  (characterized  by  the  presence  of  vesicular  matter), 
in  which  the  Auditory  nerve  terminates ;  and  these  are  sometimes  deve- 
loped as  distinct  ganglionic  enlargements.  Other  separate  ganglia, 
sometimes  of  considerable  size,  are  very  commonly  found  at  the  origin 
of  the  Par  Vagum. — It  is  curious  to  notice  the  very  large  comparative 
size  of  the  Pineal  gland  (/),  and  of  the  Pituitary  body  (A),  in  this  class ; 
the  functions  of  these  organs  are  entirely  unknown. 

870.  The  analogy  of  the  Optic  lobes  of  Fishes  to  the  Corpora  Quad- 
rigemina  and  Thalami  Optici  of  the  fully-formed  brain  of  the  higher 
Vertebrata,  is  not  so  complete  as  it  is  to  certain  parts  which  occupy  their 
place  at  an  earlier  period.  In  the  Human  Embryo,  at  about  the  6th 
week,  the  Encephalon  consists  of  a  series  of  vesicles  arranged  in  a  line 


Human  Embryo  of  sixth  week,  enlarged  about  three  times : — a,  vesicle  of  corpora  quadrigemina ;  b,  yesicle 
of  cerebral  hemispheres  ;  c,  vesicle  of  thiilami  optici  and  third  ventricle ;  d,  vesicle  for  cerebellum  and  medulla 
oblongata;  e,  auditory  vesicle ;  /,  olfactory  fossa;  h,  liver;  *♦  caudal  extremity. 

with  each  other  ;  of  which  those  that  represent  the  cerebrum  (5,  Fig. 
153)  are  the  smallest,  whilst  that  which  represents  the  cerebellum  (d)  is 
the  largest.  Between  the  cerebral  and  the  cerebellic  vesicles,  are  two 
others,  (<?,  and  a),  of  which  the  posterior  one  is  the  Optic  ganglion,  and 
answers  to  the  Tubercula  Quadrigemina ;  whilst  the  anterior  contains 
the  Third  Ventricle,  and  corresponds  in  some  degree  to  the  Thalami 
Optici.  This  condition  is  precisely  represented  in  the  Lamprey ;  but  in 
most  Fishes,  the  optic  ganglia,  and  the  parts  surrounding  the  third  ven- 
tricle, form  but  one  lobe  ;  so  that  the  third  ventricle  seems  hollowed 
out  of  the  optic  ganglia,  as  shown  in  Fig.  7,  c,  (Plate  II.) 

871.  The  Encephalon  of  Reptiles  does  not  show  any  considerable 
advance  in  its  general  structure,  above  that  of  the  higher  Fishes.  The 
Cerebral  Hemispheres  (Plate  II.  Figs.  8,  9,  10,  b)  are  always  much 
larger  than  the  Olfactive  and  Optic  ganglia ;  and  they  generally  cover- 
in  the  latter  (<?,  c)  in  part,  by  their  posterior  extremities.  The  Cere- 
bellum is  almost  invariably  of  small  proportionate  dimensions  ;  and  this 
is  especially  the  case  in  the  Frog,  in  which  it  does  not  even  cover-in  the 
fourth  ventricle.  This  low  development  of  the  Cerebellum  in  Reptiles, 
is  what  might  be  anticipated  from  the  general  inertness  of  those  ani- 
mals, and  the  want  of  variety  in  their  movements.     The  Spinal  Cord  is 


494  OF   THE    NERVOUS    SYSTEM   AND   ITS   ACTIONS. 

still  very  large,  in  proportion  to  the  nervous  masses  contained  in  the 
skull ;  and,  as  we  shall  hereafter  see,  its  power  of  keeping  up  the  move- 
ments of  the  body,  after  it  has  been  cut  oiF  from  all  connexion  with  the 
brain,  is  very  considerable. — We  find  that,  in  Reptiles,  as  in  Fishes,  the 
Spinal  Cord  may  have  a  nearly  uniform  size  from  one  extremity  to  the 
other,  like  the  ventral  cord  of  the  lower  Articulata ;  or  it  may  present 
considerable  enlargements  at  particular  spots,  like  the  ganglionic  cord 
in  the  thoracic  regions  of  Insects.  This  difference  depends  upon  the 
degree  of  development  of  the  special  locomotive  organs.  Thus  in  the 
Eel  and  Serpent,  whose  movements  are  accomplished  by  the  undulations 
of  the  entire  trunk,  and  which  are  destitute  of  members,  we  find  a  uni- 
form development  of  ganglionic  matter  in  the  spinal  cord.  On  the  other 
hand,  in  the  Flying-fish,  in  which  the  pectoral  fins  or  anterior  extremi- 
ties effect  the  greater  part  of  the  propulsion  of  the  body,  we  find  a  great 
ganglionic  enlargement  of  the  Spinal  cord,  at  the  part  with  which  the 
nerves  of  those  members  are  connected :  in  the  Frog,  whose  movements 
are  chiefly  effected  by  the  posterior  extremities,  we  find  a  similar  enlarge- 
ment at  the  roots  of  the  crural  nerves  :  and  in  the  Turtles  and  Lizards, 
the  two  pairs  of  whose  members  are  nearly  equal  in  function,  and  serve 
to  effect  the  principal  movements  of  the  body,  we  find  an  anterior  and 
posterior  enlargement  of  the  Spinal  Cord,  corresponding  to  the  parts 
with  which  the  nerves  of  these  members  are  connected. 

872.  We  find  in  Birds  a  considerable  advance  in  the  character  of  the 
Encephalon,  towards  that  which  it  presents  in  Mammalia.  The  Cere- 
bral Hemispheres  (Plate  II.,  Figs.  11,  12,  13,  h)  are  greatly  increased 
in  size ;  and  they  cover-in,  not  merely  the  olfactory  ganglia,  but  in 
great  part  also  the  optic  ganglia.  The  former  are  of  comparatively 
small  size  ;  the  organ  of  smell  in  Birds  not  being  much  developed.  The 
latter  are  very  large,  in  conformity  with  the  acuteness  of  sight  which  is 
highly  characteristic  of  the  class.  The  cerebellum  is  of  large  size,  as 
we  should  expect  from  the  number  and  complexity  of  the  muscular 
movements  performed  by  animals  of  this  class ;  but  it  is  still  undivided 
into  hemispheres.  The  Spinal  Cord  is  still  of  considerable  size  in  com- 
parison with  the  Encephalon  ;  and  it  is  much  enlarged  at  the  points 
whence  the  legs  and  wings  originate.  In  the  species  which  have  the 
most  energetic  flight,  such  as  the  Swallow,  the  enlargement  is  the 
greatest  where  the  nerves  of  the  wings  come  off;  but  in  those  which, 
like  the  Ostrich,  move  principally  by  running  on  the  ground,  the  poste- 
rior enlargement,  from  which  the  legs  are  supplied  with  nerves,  is  much 
the  more  considerable. 

873.  In  the  Mammalia  we  find  the  size  and  general  development  of 
the  Encephalon  presenting  a  gradual  increase,  as  we  ascend  the  series, 
from  the  non-placental  Monotremes  and  Marsupials,  towards  Man.  In 
the  former,  the  Hemispheres  exhibit  no  convolutions  ;  and  the  great 
transverse  commissure,  or  connecting  band  of  fibrous  structure,  termed 
the  corpus  callosum,  is  deficient.  As  we  rise  through  the  true  viviparous 
division  of  the  class,  we  notice  a  gradually-increasing  prolongation  of 
the  Cerebral  Hemispheres  backwards ;  so  that  first  the  optic  ganglia, 
and  then  the  cerebellum,  are  covered-in  by  them.  The  latter  partly 
shows  itself,  however,  in  all  but  Man  and  the  Quadrumana,  when  we 


NERVOUS   CENTRES    OF   MAMMALIA — SPINAL   CORD.  495 

look  at  the  brain  from  above  downwards :  as  we  see  in  the  Encephalon 
of  the  Sheep  (Plate.  II.,  Figs.  14,  15,  d).  The  Cerebral  hemispheres 
increase,  not  only  in  size ;  but  also  in  complexity  of  structure,  both 
external  and  internal.  Their  exterior,  instead  of  remaining  smooth,  is 
marked  by  convolutions  ;  which  serve  to  extend  very  greatly  the  amount 
of  surface  over  which  blood-vessels  can  pass  into  the  gray  substance. 
Their  internal  structure  becomes  more  complex,  in  the  same  proportion 
as  their  size  and  the  depth  of  their  convolutions  increase ;  and  in  Man 
all  these  conditions  present  themselves  in  a  far  higher  degree  than  in 
any  other  animal.  The  number  of  commissural  bands,  connecting  the 
two  hemispheres  with  each  other  transversely,  and  uniting  their  anterior 
and  posterior  portions,  is  very  greatly  increased ;  and  in  fact,  a  large 
proportion  of  their  mass  is  composed,  in  Man  and  the  higher  Mammalia, 
of  fibres  of  this  character. — In  proportion  to  the  increase  of  the  Cere- 
bral hemispheres,  there  is  a  relative  diminution  in  the  size  of  the  ganglia 
of  special  sense ;  but  their  dimensions,  as  compared  with  the  entire  bulk 
of  the  animal,  are  by  no  means  reduced,  but  are  even  increased.  The 
Olfactive  ganglia  (Fig.  14,  a)  are  always  readily  discoverable ;  being 
separated  from  the  remainder  of  the  encephalic  masses  by  a  peduncle 
on  each  side.  The  Optic  ganglia  (Fig.  15,  e),  on  the  other  hand,  are 
so  completely  covered-in  by  the  Hemispheres,  that  it  is  only  when  the 
latter  are  turned  aside  that  we  can  discern  them.  They  differ  in  exter- 
nal aspect  from  the  optic  ganglia  of  Birds  and  the  lower  Vertebrata ; 
being  divided  by  a  transverse  furrow  into  anterior  and  posterior  emi- 
nences, whence  they  are  known  as  the  Corpora  Quadrigemina.  The 
Auditory  ganglia  are  lodged  in  the  substance  of  the  Medulla  Oblongata, 
forming  the  "gray  nuclei"  of  the  strands  termed  the  "posterior  pyra- 
mids ;"  and  similar  nuclei  in  the  ^'restiform  bodies"  are  the  ganglionic 
centres  of  the  Glosso-pharyngeal  nerves,  and  perhaps  minister  to  the 
sense  of  Taste.  Besides  these,  however,  are  the  two  large  bodies  termed 
the  Corpora  Striata  and  Thalami  Optici,  which  have  been  commonly 
considered  as  appendages  of  the  Cerebrum,  but  which  must  undoubtedly 
be  regarded  as  independent  of  it,  and  as  themselves  constituting  gan- 
glionic centres,  whose  development  bears  no  constant  proportion  to  that 
of  the  Cerebrum.  From  the  peculiar  relation  presently  to  be  described 
(§  901),  which  these  bodies  bear  on  the  one  hand  to  the  Spinal  Cord, 
and  on  the  other  to  the  rest  of  the  Encephalon,  there  seems  strong 
reason  to  believe  that  they  together  constitute  thfe  ganglionic  centre  of 
the  sense  of  Touch,  and  of  the  motions  which  are  automatically  prompted 
by  it. — The  Cerebellum  is  chiefly  remarkable  for  the  development  of  its 
lateral  parts  or  hemispheres,  and  for  the  intricate  arrangement  of  the 
gray  and  white  matter  in  them  (Fig.  15,  d);  the  central  portion,  some- 
times called  the  vermiform  process,  is  relatively  less  developed  than  in 
the  lower  Vertebrata,  where  it  forms  the  entire  organ. — The  Spinal 
Cord  is  much  reduced  in  size,  when  compared  with  other  parts  of  the 
nervous  centres  ;  the  motions  of  the  animals  of  this  class  being  more 
dependent  upon  their  will  or  guided  by  their  sensations ;  and  the  simply 
reflex  actions  bearing  a  much  smaller  proportion  to  the  rest.  The 
development  of  ganglionic  enlargements,  in  accordance  with  the  presence 
or  absence  of  high  locomotive  powers  in  the  extremities,  follows  the 
same  rule  as  in  the  preceding  classes. 


496  OF  THE   NERVOUS   SYSTEM  AND   ITS   ACTIONS. 


3.  Functions  of  the  Spinal  Cord  and  its  Nerves. 

874.  In  commencing  our  more  detailed  examination  into  the  func- 
tions of  the  different  parts  of  the  Nervous  system  in  Vertebrated  ani- 
mals, it  seems  best  to  commence  with  the  Spinal  Cord ;  this  being  the 
portion  whose  presence  is  most  essential  to  the  continuance  of  life.  As 
already  mentioned,  Infants  are  sometimes  born  without  any  Cerebrum 
or  Cerebellum ;  and  such  have  existed  for  several  hours  or  even  days, 
breathing,  crying,  sucking,  and  performing  various  other  movements. 
The  Cerebrum  and  Cerebellum  have  been  experimentally  removed  from 
Birds  and  young  Mammalia,  thus  reducing  these  beings  to  a  similar 
condition ;  and  all  their  vital  operations  have,  nevertheless,  been  so 
regularly  performed,  as  to  enable  them  to  live  for  weeks,  or  even 
months.  In  the  Amphioxus,  as  already  remarked,  we  have  an  example 
of  a  completely-formed  adult  animal,  in  which  no  rudiment  of  a  Cere- 
brum or  Cerebellum  can  be  detected.  And  in  ordinary  profound  sleep, 
or  in  apoplexy,  the  functions  of  these  organs  are  so  completely  sus- 
pended, that  the  animal  is,  in  all  essential  particulars,  in  the  same  con- 
dition for  a  time  as  if  destitute  of  them.  It  is  possible,  indeed,  to  re- 
duce a  vertebrated  animal  to  the  condition  (so  far  as  its  nervous  system  is 
concerned)  of  an  Ascidian  Mollusc  (§  850) ;  for  it  may  continue  to  exist 
for  some  time,  when  not  merely  the  Cerebrum  and  Cerebellum  have 
been  removed  from  above,  but  when  nearly  the  whole  Spinal  Cord  has 
been  removed  from  below, — that  part  only  of  the  latter  being  left,  which 
is  the  centre  of  the  respiratory  actions,  and  which  corresponds  to  the 
single  ganglion  of  the  Tunicata.  On  the  other  hand,  no  animal  can 
exist  by  its  Encephalon  alone,  the  Spinal  Cord  being  destroyed  or  re- 
moved ;  for  the  reflex  actions  of  the  latter  are  so  essential  to  the  con- 
tinuance of  its  respiration,  and  consequently  of  its  circulation,  that  if 
they  be  suspended  (by  the  destruction  of  the  portion  of  the  cord  which 
is  concerned  in  them),  all  the  organic  functions  must  soon  cease. 

875.  Although  the  Spinal  Cord  was  formerly  regarded  as  little  else 
than  a  bundle  of  nerves  proceeding  from  the  Brain,  yet  its  true  rank, 
as  a  distinct  centre  of  nervous  power,  is  now  universally  admitted. 
That  the  actions  prompted  by  it,  when  these  do  not  originate  in  one 
of  the  higher  centres,  are  of  a  purely  reflex  nature, — consisting  in  the 
excitement  of  muscular  movements  in  respondence  to  external  impres- 
sions, without  the  necessary  intervention  of  sensation, — appears  to  be 
a  necessary  inference  from  the  facts  that  have  been  brought  to  light  by 
experiment  and  observation.  Experiments  on  the  nature  of  this  func- 
tion are  best  made  upon  cold-blooded  animals ;  as  their  general  functions 
are  less  disturbed  by  the  effects  of  severe  injuries  of  the  nervous  sys- 
tem, than  are  those  of  Birds  and  Mammals.  When  the  Cerebrum  has 
been  removed,  or  its  functions  have  been  suspended  by  a  severe  blow 
upon  the  head,  a  variety  of  motions  may  be  excited  by  their  appropriate 
stimuli.  Thus,  if  the  edge  of  the  eyelid  be  touched  with  a  straw,  the 
lid  immediately  closes.  If  a  candle  be  brought  near  the  eye,  the  pupil 
contracts.  If  liquid  be  poured  into  the  mouth,  or  a  solid  substance  be 
pushed  within  the  grasp  of  the  muscles  of  deglutition,  it  is  swallowed. 


REFLEX   FUNCTION  OF   THE   SPINAL   CORD.  497 

If  the  foot  be  pinched,  or  burned  with  a  lighted  taper,  it  is  withdrawn ; 
and  (if  the  animal  experimented  on  be  a  Frog)  the  animal  will  leap 
away,  as  if  to  escape  from  the  source  of  irritation.  If  the  cloaca  be 
irritated  with  a  probe,  the  hind-legs  will  endeavour  to  push  it  away.  _ 

876.  Now  the  performance  of  these,  as  well  as  of  other  movements, 
many  of  them  most  remarkably  adapted  to  an  evident  purpose,  might 
be  supposed  to  indicate,  that  sensations  are  called  up  by  the  impres- 
sions ;  and  that  the  animal  can  not  only  feel,  but  can  voluntarily  direct 
its  movements,  so  as  to  get  rid  of  the  irritation  which  annoys  it.  But 
such  an  inference  would  be  inconsistent  with  other  facts. — In  the  first 
place,  the  motions  performed  by  an  animal  under  such  circumstances 
are  never  spontaneous,  but  are  always  excited  by  a  stimulus  of  some 
kind.  Thus,  a  decapitated  Frog,  after  the  first  violent  convulsive 
movements  occasioned  by  the  operation  have  passed  away,  remains  at 
rest  until  it  is  touched :  and  then  the  leg,  or  its  whole  body  may  be 
thrown  into  sudden  action,  which  immediately  subsides  again.  In  the 
same  manner,  the  act  of  swallowing  is  not  performed,  except  when  it 
is  excited  by  the  contact  of  food  or  liquid ;  and  even  the  respiratory 
movements,  spontaneous  as  they  seem  to  be,  would  not  continue,  unless 
they  were  continually  re-excited  by  the  presence  of  venous  blood 
in  the  vessels.  These  movements  are  necessarily  linked  with  the 
stimulus  that  excites  them ;  that  is,  the  same  stimulus  will  always  pro- 
duce the  same  movement,  when  the  condition  of  the  body  is  the  same. 
Hence  it  is  evident,  that  the  judgment  and  will  are  not  concerned  in 
producing  them ;  and  that  the  adaptiveness  of  the  movements  is  no 
proof  of  the  existence  of  consciousness  and  discrimination  in  the  being 
that  executes  them, — the  adaptation  being  made  for  the  being,  by  the 
peculiar  structure  of  its  nervous  apparatus,  which  causes  a  certain  move- 
ment to  be  executed  in  respondence  to  a  given  impression, — not  by  it. 
An  animal  thus  circumstanced  may  be  not  unaptly  compared  to  an  auto- 
maton; in  which  particular  movements,  adapted  to  produce  a  given 
efi'ect,  are  produced  by  touching  certain  springs.  Here  the  adaptation 
was  in  the  mind  of  the  maker  or  designer  of  the  automaton ;  and  so  it 
evidently  is,  in  regard  to  the  reflex  or  consensual  movements  of  animals, 
as  well  as  with  respect  to  the  various  operations  of  their  nutritive  sys- 
tem, over  which  they  have  no  'control,  yet  which  concur  most  admira- 
bly to  a  common  end. 

877.  Again,  we  find  that  such  movements  /nay  be  performed,  not 
only  when  the  Brain  has  been  removed,  the  Spinal  cord  remaining  en- 
tire, but  also  when  the  Spinal  cord  has  been  itself  cut  across,  so  as  to 
be  divided  into  two  or  more  portions,  each  of  them  completely  isolated 
from  each  other,  and  from  other  parts  of  the  nervous  centres.  ,  Thus, 
if  the  head  of  a  Frog  be  cut  off,  and  its  spinal  cord  be  divided  in  the 
middle  of  the  back,  so  that  its  fore-legs  remain  connected  with  the 
upper  part,  and  its  hind-legs  with  the  lower,  each  pair  of  members  may 
be  excited  to  movement  by  a  stimulus  applied  to  itself;  but  the  two 
pairs  will  not  exhibit  any  consentaneous  motions,  as  they  will  do  when 
the  spinal  cord  is  undivided.  Or,  if  the  Spinal  cord  be  cut  across, 
without  the  removal  of  the  Brain,  the  lower  limbs  may  be  excited  to  move- 
luent,  by  an  appropriate  stimulus,  though  they  are  completely  paralysed 

32 


498  OF  THE  NERVOUS   SYSTEM   AND   ITS  ACTIONS. 

to  the  tvill;  whilst  the  upper  remains  under  the  control  of  the  animal, 
as  completely  as  before.  Now  it  is  not  conceivable  that,  in  this  last 
case,  sensation  and  volition  should  exist  in  that  portion  of  the  spinal 
cord,  which  remains  connected  with  the  nerves  of  the  posterior  extremi- 
ties, but  which  is  cut  off  from  the  brain.  For  if  it  were  so,  there  must 
be  two  distinct  centres  in  the  same  animal,  the  attributes  of  the  brain 
not  being  affected ;  and,  by  dividing  the  spinal  cord  into  two  or  more 
segments,  we  might  thus  create  in  the  body  of  one  animal  two  or  more 
distinct  centres  of  sensation,  independent  of  that  which  still  holds  its 
proper  place  in  the  Encephalon.  To  say  that  two  or  more  distinct 
centres  of  sensation  are  present  in  such  a  case,  would  really  be  in  effect 
the  same  as  saying,  that  there  are  two  or  more  distinct  minds  in  one 
body, — which  is  manifestly  absurd. 

878.  But  the  best  proofs  of  the  limitation  of  the  endowments  of  the 
Spinal  Cord,  are  derived  from  the  phenomena  presented  by  the  Human 
subject,  in  Cases  where  that  organ  has  suffered  injury,  by  disease  or 
accident,  in  the  middle  of  the  back.  We  find  that,  when  this  injury  has 
been  severe  enough  to  produce  the  effect  of  a  complete  division  of  the 
Cord,  there  is  not  only  a  total  want  of  voluntary  control  over  the  lower 
extremities,  but  a  complete  absence  of  sensation  also, — the  individual 
not  being  in  the  least  conscious  of  any  impression  made  upon  them. 
When  the  lower  segment  of  the  Cord  remains  sound,  and  its  nervous  con- 
nexions with  the  limbs  are  unimpaired,  distinct  reflex  movements  may 
be  excited  in  the  limbs,  by  stimuli  directly  applied  to  them,  as,  for  in- 
stance, by  pinching  the  skin,  tickling  the  sole  of  the  foot,  or  applying 
a  hot  plate  to  its  surface ;  and  this  without  the  least  sensation,  on  the 
part  of  the  patient,  either  of  the  cause  of  the  movement,  or  of  the  move- 
ment itself.  This  fact,  taken  in  connexion  with  the  preceding  experi- 
ments, both  upon  Yertebrated  and  Articulated  animals,  distinctly  proves 
that  Sensation  is  not  a  necessary  link  in  the  chain  of  reflex  actions  ;  but 
that  all  which  is  required  is  an  afferent  fibre,  capable  of  receiving  the 
impression  made  upon  the  surface,  and  of  conveying  it  to  the  centre ;  a 
ganglionic  centre^  composed  of  vesicular  nervous  substance,  into  which 
the  afferent  fibre  passes ;  and  an  efferent  fibre,  capable  of  transmitting 
the  motor  impulse,  from  the  ganglionic  centre,  to  the  muscle  which  is 
to  be  thrown  into  contraction.  * 

879.  These  conditions,  are  realized  in  the  Spinal  Cord.  We  may 
have  reflex  actions  excited  through  any  one  isolated  segment  of  it,  as 
through  a  single  ganglion  of  the  ventral  cord  of  Articulata ;  but  they 
are  then  confined  to  the  part  supplied  by  the  nerves  of  that  segment. 
Thus,  if  the  spinal  cord  of  a  Frog  be  divided  just  above  the  origin  of 
the  crural  nerves,  the  hind-legs  may  be  thrown  into  reflex  contraction 
by  various  stimuli  applied  to  themselves ;  but  the  forelegs  will  exhibit 
no  movement  of  this  kind.  But  when  the  brain  has  been  removed,  and 
the  Spinal  Cord  is  left  entire,  movements  may  be  excited  in  distant 
parts,  as,  for  example,  in  the  fore-legs,  by  any  powerful  irritation  of  the 
posterior  extremities,  and  vice  versd.  This  is  particularly  well  seen  in 
the  convulsive  movements,  which  take  place  in  certain  disordered  states 
of  the  nervous  system ;  a  slight  local  irritation  being  sufficient  to  throw 
almost  any  muscle  of  the  body  into  a  state  of  energetic  action  (§  885). 


REFLEX   FUNCTION   OF   THE   SPINAL   CORD.  499 

And  a  similar  state  may  be  artificially  induced,  by  applying  Strychnine 
(in  solution)  to  the  Spinal  Cord  of  a  decapitated  Frog. 

880.  The  minute  anatomy  of  the  Spinal  Cord  is  a  subject  of  great 
difficulty ;  and  our  notions  of  the  course  of  the  fibres  within  it  are  rather 
founded  upon  physiological  phenomena,  and  upon  the  more  evident 
structure  of  the  ventral  column  in  Articulata,  than  upon  what  can  be 
clearly  demonstrated  in  Vertebrated  animals.  The  roots  of  the  Spinal 
nerves  are  all  distinctly  separable  into  an  anterior  and  a  posterior  fasci- 
culus ;  and  it  is  certain  that  these  fasciculi  have  entirely  opposite  func- 
tions. If  they  be  laid  bare,  and  the  anterior  fasciculus  of  any  spinal 
nerve  be  touched,  violent  contractions  are  immediately  seen  in  the  mus- 
cles supplied  by  that  nerve;  these  contractions  are  as  strongly  manifested 
if  the  anterior  roots  be  divided,  and  their  separated  end  be  irritated ; 
whilst  no  such  result  follows,  whatever  amount  of  irritation  be  applied  to 
the  ends  still  in  connexion  with  the  cord.  Notwithstanding  these  violent 
movements,  the  animal  shows  little  or  no  sign  of  pain.  On  the  other 
hand,  if  the  posterior  roots  be  irritated,  the  animal  gives  signs  of  acute 
pain,  and  no  vigorous  muscular  contractions  are  produced.  The  move- 
ments which  are  witnessed  are  evidently  of  a  reflex  nature,  being  called 
forth  through  the  anterior  roots ;  as  is  proved  by  their  cessation  when 
these  are  divided.  Further,  if  the  posterior  roots  be  divided,  and  the 
separated  ends  be  irritated,  no  efi^ect  whatever  is  produced ;  no  move- 
ment is  excited ;  and  no  sensation  is  occasioned ;  but  if  the  ends  still  in 
connexion  with  the  cord  be  irritated,  the  animal  shows  signs  of  pain  as 
before. — Hence  it  is  evident,  that  the  posterior  roots  are  made  up  of 
afferent  fibres,  that  is,  of  the  fibres  which  convey  impression  towards 
the  nervous  centres ;  which  impressions,  if  confined  to  the  cord  itself, 
excite  reflex  actions  ;  whilst,  if  conveyed  to  the  brain,  they  produce  sen- 
sations. On  the  other  hand  it  is  equally  evident,  that  the  anterior  roots 
are  composed  of  efferent  or  motor  fibres,  which  serve  to  convey  to  the 
muscles  the  motor  impulses  originating  in  the  nervous  centres ;  these 
impulses  may  be  occasioned  by  the  reflex  action  of  the  Spinal  cord  ;  or 
they  may  descend  from  the  Brain,  where  they  have  been  generated  by 
a  Consensual  or  Emotional  impulse,  or  by  an  act  of  the  Will. 

881.  The  Spinal  Cord  is  a  completely  double  tract ;  being  composed 
of  two  distinct  halves,  united  together  on  the  median  plane  by  nume- 
rous commissural  fibres.  This  union  is  much  closer  in  Man  and  the 
Mammalia,  than  it  is  in  the  lower  Vertebrata  ;  ^ut  the  division  is  still 
marked  externally,  by  a  deep  fissure  on  the  anterior  surface  of  the  cord, 
and  by  a  shallower  one  on  its  posterior  aspect.  Its  surface  is  traversed, 
moreover,  by  two  furrows  on  each  side  ;  so  that  each  half  is  divided  into 
three  columns,  the  anterior ,  lateral^  and  posterior.  The  anterior  roots 
of  the  spinal  nerves  join  the  Cord  for  the  most  part  along  the  line  of 
the  anterior  furrow ;  and  the  posterior  along  the  line  of  the  posterior 
furrow :  so  that  the  middle  or  lateral  column  lies  between  them,  the 
anterior  column  being  altogether  in  front  of  them,  and  the  posterior 
column  behind  them.  When  a  tranverse  section  of  the  Cord  is  made, 
it  is  seen  to  contain,  on  each  side,  a  crescentic  patch  of  gray  or  vesicu- 
lar substance  ;  the  points  of  each  crescent  are  directed  towards  the 
anterior  and  posterior  furrows  of  its  own  side  respectively ;  whilst  th« 
convexities  of  the  two  crescents  approach  one  another  near  the  median 


500  OP   THE   NERVOUS   SYSTEM   AND   ITS  ACTIONS. 

plane,  and  are  connected  by  a  transverse  tract  of  gray  matter.  The 
remainder  of  the  cord  is  made  up  of  white  or  tubular  substance,  the 
course  of  whose  fibres  is  for  the  most  part  longitudinal.  The  posterior 
peak  of  the  crescentic  patch  of  gray  matter  approaches  very  closely 
to  the  bottom  of  the  posterior  furrow ;  whilst  the  anterior  peak  does 
not  come  into  nearly  the  same  degree  of  proximity  with  the  bottom  of 
the  anterior  furrow.  Hence  it  is  considered  by  some,  that  the  lateral 
or  middle  columns  of  the  cord,  being  much  less  completely  isolated 
from  the  anterior  columns  than  they  are  from  the  posterior,  should  be 
associated  with  the  former,  under  the  name  of  antero-lateral  columns. 

882.  Upon  tracing  the  roots  of  the  nerves  into  the  substance  of  the 
Cord,  the  connexion  of  a  part  of  their  fibres  with  its  gray  or  vesicular 
substance  is  easily  made  evident.  Of  these  fibres,  therefore,  it  serves 
as  the  proper  ganglionic  centre.  There  is  reason  to  believe,  both  from 
anatomical  investigation,  and  from  physiological  phenomena,  that,  as 
in  the  Articulata  (§  857),  a  part  of  the  afferent  or  excitor  fibres,  after 
traversing  the  gray  substance,  pass  out  on  the  same  side  as  the  efi*erent 
or  motor ;  whilst  another  portion  crosses  to  the  opposite  side,  and  forms 
part  of  its  efferent  trunks. — It  is  pretty  certain  that  other  fibres  of  the 
roots  become  continuous  with  the  longitudinal  fibres  that  form  the  white 
strands  of  the  Spinal  Cord ;  but  it  is  by  no  means  certain,  on  that 
account,  that  they  pass  on  to  the  Brain ;  and,  in  fact,  there  is  adequate 
evidence  that  if  any  of  the  fibres  thus  establish  a  direct  communication 
between  the  Encephalic  centres  and  the  spinal  nerve-trunks,  their  pro- 
portion must  be  very  small,  the  chief  part  of  the  longitudinal  strands  of 
the  Cord  being  apparently  made  up  of  commissural  fibres  which  esta- 
blish an  intimate  connexion  between  its  different  segments,  as  in  Insects. 
This  will  appear  from  the  facts  to  be  next  stated.  The  thickness  of  the 
Spinal  Cord  differs  considerably  at  its  different  parts.  Thus  in  the 
cervical  region,  there  is  an  enlargement  corresponding  with  the  origins 
of  the  nerves  that  form  the  brachial  plexus  ;  this  enlargement  is  partly 
caused  by  an  increase  in  the  amount  of  gray  matter ;  but  the  amount  of 
fibrous  structure  also,  is  much  greater  than  at  the  upper  part  of  the 
cervical  region.  On  the  other  hand,  there  is  a  still  greater  enlarge- 
ment of  the  cord  in  the  lumbar  region,  at  the  part  whence  the  nerves 
of  the  lower  extremities  arise ;  and  this  enlargement  is  caused  by  the 
great  increase  in  the  amount  both  of  the  gray  matter  and  of  the  white 
at  that  point.  It  may  be  easily  shown  by  direct  measurement,  that 
the  fibrous  strands  of  the  upper  cervical  region  would  not  by  any  means 
serve  to  carry  onwards  to  the  brain  those  of  the  lumbar  region  alone, 
much  less  with  the  addition  of  other  fibres  proceeding  from  all  the  in- 
termediate nerves.  Further,  if  the  fibrous  strands  were  for  the  most 
part  (as  formerly  supposed)  directly  continuous  between  the  brain  and 
the  roots  of  the  spinal  nerves,  the  white  portion  of  the  Spinal  Cord,  in 
such  animals  as  Serpents,  in  which  it  has  no  ganglionic  enlargements, 
should  progressively  diminish  in  diameter  with  every  pair  of  nerves 
into  which  it  sends  fibres,  from  its  cephalic  to  its  caudal  extremity ; 
this,  however,  is  by  no  means  the  case,  the  Spinal  cord  of  Serpents 
being  remarkable  for  its  uniform  diameter  throughout. — It  is  obvious, 
then,  that  if  any  of  the  longitudinal  fibres  of  the  cord  should  thus  pass 


REFLEX   FUNCTION  OF   THE   SPINAL  CORD.  501 

direct  from  the  Encephalon  to  the  nerve-roots,  their  proportion  must  be 
very  small.  And  we  shall  see  that  all  the  phenomena  which  have  been 
supposed  to  indicate  an  immediate  communication  between  the  brain 
and  the  nerves,  admit  of  another  and  more  satisfactory  explanation._   _ 

883.  It  was  supposed  by  Sir  C.  Bell  (who  was  the  first  to  determine 
the  relative  functions  of  the  two  roots  of  the  spinal  nerves  in  Verte- 
brated  animals),  that  the  anterior  columns  of  the  Spinal  cord  have  a 
function  corresponding  to  that  of  the  anterior  roots  of  the  spinal  nerves  ; 
and  the  posterior  columns  with  the  posterior  roots.  But  from  the  diffi- 
culty of  tracing  the  connexion  between  the  longitudinal  fibres  of  the 
cord  and  any  portion  of  the  roots,  it  is  at  present  impossible  to  say 
how  far  there  is  any  anatomical  reason  for  the  assumption  of  this  cor- 
respondence ;  and  it  is  quite  certain  that  the  physiological  facts  at 
present  known,  from  observation  of  the  effects  of  disease  or  injury  upon 
different  tracts  of  the  spinal  cord,  do  not  bear  out  the  supposition.  As 
to  what  the  precise  functions  of  the  several  columns  are,  however,  it  is 
not  easy  to  form  any  other  conjecture,  that  shall  be  consistent  with  all 
the  phenomena  at  present  known. 

884.  Of  the  particular  Reflex  actions  to  which  the  Spinal  Cord  (using 
that  term  in  its  limited  sense,  as  excluding  the  Medulla  Oblongata)  is 
subservient,  those  most  connected  with  the  organic  functions  have 
already  been  noticed.  They  are  chiefly  of  an  expulsive  kind ;  being 
destined  to  force  out  the  contents  of  various  cavities  of  the  body.  Thus 
the  ordinary  acts  of  defecation  and  urination,  the  ejaculatio  seminis  and 
parturition,  are  all  reflex  actions,  over  which  the  will  has  a  greater  or 
less  degree  of  control ;  being  able  to  keep  the  two  former  ones  in  check, 
so  long  as  the  stimulus  is  not  very  violent,  and  being  also  capable  of 
effecting  them  by  itself;  but  having  no  control  over  the  two  latter, 
either  by  way  of  acceleration  or  prevention,  when  once  the  stimulus  by 
which  they  are  excited  has  come  into  full  action. — The  movements  of 
the  posterior  extremities  are  among  the  most  remarkable  of  those,  which 
seem  due  to  the  action  of  the  proper  Spinal  Cord.  It  has  been  already 
noticed,  that  these  may  be  excited,  even  in  Man,  when  the  spinal 
cord  has  been  severed  in  the  middle  without  injury  to  its  lower  segment ; 
and  it  is  remarkable,  that  gentle  stimuli,  applied  to  the  skin  of  the  sole 
of  the  foot,  appear  the  most  capable  of  producing  them.  We  have  seen 
how  completely,  in  the  lower  animals,  the  acts  of  progression  may  be 
sustained,  by  the  repeated  stimulus  of  the  contact  of  the  ground,  or  of 
fluid,  without  any  influence  from  the  cephalic  ganglia ;  the  power  of 
these  being  limited,  it  would  seem,  to  the  control  and  direction  of  them. 
And  there  is  strong  reason  to  believe  that  so  far  as  the  ordinary  acts 
of  locomotion  are  concerned,  the  movements  of  the  inferior  extremities 
in  Man  may  be  performed  on  the  same  plan,  being  continued  by  the 
reflex  influence  of  the  successive  impulses  of  the  feet  upon  the  ground, 
when  once  set  in  action  by  the  will,  whilst  we  are  walking  steadily  on- 
wards,— the  mind  being  at  the  same  time  occupied  by  some  train  of 
thought,  which  engrosses  its  whole  attention.  There  are  few  persons, 
to  whom  it  has  not  occasionally  happened  that,  on  awaking  (as  it  were) 
from  their  revery,  they  have  found  themselves  in  a  place  very  different 
from  that  to  which  they  had  intended  going ;  and  even  when  the  con- 


502  OF  THE  NERVOUS  SYSTEM  AND   ITS  ACTIONS. 

sciousness  is  sufficiently  on  the  alert  to  allow  sensations  to  guide,  direct, 
and  control  the  motions  of  the  limbs,  their  actions  appear  to  be 
performed  without  the  agency  of  the  will,  which  may  be  entirely  con- 
centrated upon  some  interior  mental  operation.  It  is  certain  that,  in 
Birds,  the  movements  of  flight  may  be  performed  after  the  removal  of 
the  Cerebrum. 

885.  There  are  many  irregular  or  abnormal  reflex  actions,  performed 
through  the  instrumentality  of  the  Spinal  Cord,  the  study  of  which  is  of 
the  highest  importance  to  the  Medical  Man.  It  is  probable  that  all  Con- 
vulsive movements  are  produced  through  its  agency  and  that  of  the 
Medulla  Oblongata ;  for  it  has  been  found,  by  repeated  experiments, 
that  these  movements  are  never  produced  by  injuries  of  the  Cerebral 
hemispheres. — Convulsive  movements  may  be  of  three  kinds.  1.  They 
may  be  simply  reflex ;  being  the  natural  result  of  some  extraordinary 
irritation.  2,  They  may  be  simply  centric  ;  depending  upon  a  peculiar 
condition  of  the  ganglionic  centre  of  the  Spinal  Cord,  which  occasions 
muscular  movements  without  any  stimulation.  This  may  be  dependent 
upon  an  abnormal  state  of  the  Blood.  We  know  that  it  may  be  pro- 
duced by  the  introduction  of  certain  poisons  (as  strychnia)  into  the  cir- 
culation ;  and  it  is  probable  that  morbid  matters  generated  within  the 
body  may  have  the  same  eff'ect.  3.  They  may  depend  upon  the  com- 
bined action  of  both  principles ;  the  nervous  centres  being  in  a  very 
irritable  state,  which  causes  very  slight  irritations  (such  as  would  other- 
wise be  inoperative)  to  excite  violent  reflex  or  convulsive  movements. 
This  last  is  by  far  the  most  common  cause  of  the  convulsive  actions, 
that  occur  in  various  diseased  conditions  of  the  system.  Thus,  convul- 
sions are  not  unfrequent  in  children,  during  the  period  of  teething; 
being  produced  by  the  irritation,  which  results  from  the  pressure  of  the 
tooth,  as  it  rises  against  the  unyielding  gum.  In  this  case,  the  stimulus 
would  scarcely  be  sufficient  to  produce  the  violent  result,  were  it  not 
for  a  peculiarly  excitable  state  of  the  Spinal  Cord,  brought  about  by 
various  causes.  In  like  manner,  when  such  an  excitable  state  exists, 
convulsions  may  be  occasioned  by  the  presence  of  intestinal  worms,  of 
irritating  substances,  or  even  simply  of  undigested  matters,  in  the  ali- 
mentary canal ;  and  will  cease  as  soon  as  they  are  cleared  out,  in  the 
same  manner  as  the  convulsions  of  teething  may  often  be  at  once 
checked,  by  the  free  lancing  of  the  gums. 

886.  The  influence  of  the  condition  of  the  Spinal  Cord  itself,  is 
peculiarly  seen  in  the  convulsive  diseases  termed  Hydrophobia,  Teta- 
nus, Epilepsy,  and  Hysteria.— In  the  first  of  these,  not  only  the  Spinal 
Cord,  but  the  Medulla  Oblongata,  and  the  ganglia  of  Special  Sense, 
are  involved ;  their  peculiar  condition  being  the  result,  it  would  appear, 
of  the  introduction  of  a  poison  into  the  blood.  It  is  most  remarkable 
that  the  Cerebrum  should  so  completely  escape  its  influence.  When 
the  state  of  intense  excitability  in  these  centres,  is  once  established, 
the  slightest  stimulus  is  sufficient  to  bring  about  convulsive  movements 
of  the  utmost  violence.  It  is  characteristic  of  this  complaint,  that  the 
stimuli  most  efiectual  in  exciting  the  movements,  are  those  which  act 
through  the  nerves  of  special  sense;  thus  the  sight  or  the  sou7id  oi 
water  will  bring  on  the  paroxysm ;  and  any  attempt  to  taste  it  increases 


hydrophobia;  tetanus;  epilepsy;  hysteria.  503 

the  severity  of  the  convulsions. — In  tetanus  there  appears  to  be  a  simi- 
larly excitable  state  of  the  Spinal  Cord  and  Medulla  Oblongata,  not 
involving  the  ganglia  of  special  sense.  This  may  be  the  result  of 
causes  altogether  internal,  as  in  the  idiopathic  form  of  the  disease ;  j,n 
which  the  condition  exactly  resembles  that,  which  may  be  artificially 
induced  by  the  administration  of  Strychnine,  or  by  its  application  to 
the  cord.  Or  it  may  be  first  occasioned  by  some  local  irritation,  as 
that  of  a  lacerated  wound ;  the  irritation  of  the  injured  nerve  being 
propagated  to  the  nervous  centres,  and  establishing  the  excitable  state 
in  them.  When  the  complaint  has  once  established  itself,  the  removal 
of  the  original  cause  of  irritation  (as  by  the  amputation  of  the  injured 
limb)  is  seldom  of  any  avail ;  since  the  slightest  impressions  upon  al- 
most any  part  of  the  body,  are  sufficient  to  excite  the  tetanic  spasm. — 
In  like  manner.  Epilepsy,  which  consists  in  convulsive  actions  with 
temporary  suspension  of  the  functions  of  the  EncCphalon,  may  result 
from  the  irritation  of  local  causes,  like  the  convulsions  of  teething ;  and 
may,  like  them,  cease  when  the  sources  of  irritation  are  removed.  But 
when  it  becomes  confirmed,  it  seems  to  involve  a  disorder  of  the  nervous 
centres,  which  no  local  treatment  can  influence. 

887.  These  and  other  forms  of  Convulsive  disorder,  when  productive 
of  a  fatal  result,  usually  act  by  suspending  the  respiratory  movements ; 
the  muscles  which  eff'ect  these  being  fixed  by  the  spasms,  so  that  the 
air  cannot  pass  either  in  or  out,  and  suffocation  takes  place  as  completely 
as  if  the  entrance  to  the  air-passages  were  closed.  It  is  remarkable 
that  every  one  of  them  may  be  imitated  by  Hysteria ;  a  state  of  the 
nervous  system,  in  which  there  is  a  peculiar  excitability,  but  in  which 
there  is  no  such  fixed  tendency  to  irregular  action,  as  would  indicate 
any  positive  disease, — one  form  of  convulsion  often  taking  the  place  of 
another,  at  short  intervals,  with  the  most  wonderful  variety.  It  will 
often  be  found,  that  the  convulsions  may  be  immediately  traced  to 
some  local  irritation ;  thus  they  are  particularly  liable  to  occur  at  the 
catamenial  periods,  especially  if  the  menstrual  flux  be  deficient ;  but  it 
does  not  seem  improbable,  that  here  too  the  presence  of  morbid  matters 
in  the  blood  has  much  to  do  with  the  development  of  that  peculiar 
excitability,  which  gives  to  slight  local  irritations  such  a  powerful 
agency. 

888.  The  statement  that  the  Spinal  Nerves  arise  by  double  roots,  is 
not  without  exception  as  regards  some,  which/  arise  from  its  cranial 
prolongation,  and  which  are  distributed  to  the  parts  of  the  head  and 
neck.  The  first  spinal  nerve,  or  sub-occipital  (the  10th  pair  of  Willis) 
not  unfrequently  arises  by  a  single  set  of  roots,  from  the  anterior  por- 
tion of  the  cord ;  and  it  is  then  purely  motor,  except  in  virtue  of  its 
inosculation  with  other  nerves.  The  Hypoglossal  (9th  pair  of  Willis) 
appears  to  be  also  a  purely  motor  nerve ;  arising  by  one  set  of  roots, 
and  being  distributed  entirely  to  the  muscles  of  the  tongue,  which 
organ  derives  its  sensibility  from  other  nerves.  The  Grlosso-Pharyn- 
geal  usually  arises  from  a  single  set  of  roots,  and  these  correspond 
with  the  posterior  roots  of  the  spinal  nerves ;  in  some  animals,  however, 
and  occasionally  in  man,  there  is  a  distinct  anterior  root,  and  the 
nerve,  acquires  direct   motor  functions.     It  may  in  some  respects  be 


604  OF   THE   NERVOUS   SYSTEM  AND   ITS   ACTIONS. 

considered  as  making  up,  with  the  preceding,  an  ordinary  spinal  nerve. 
The  Spinal  Accessory^  again,  appears  to  be  chiefly  or  entirely  a  motor 
nerve  at  its  origin;  and  in  like  manner  the  Fneumogastric,  or  Par 
Vagum,  seems  at  its  roots  to  correspond  with  the  posterior  roots  of  the 
ordinary  spinal  nerves,  and  to  execute  functions  analogous  to  theirs  ; 
but  these  two  nerves  exchange  fibres,  so  that  each  acquires  in  part  the 
endowments  of  the  other.  The  Facial  nerve  (or  portio  dura  of  the  7th), 
which  is  the  nerve  that  supplies  the  muscles  of  the  head  in  general, 
arises  by  a  single  root,  and  is  exclusively  motor  in  its  properties, — 
except  in  branches  which  have  received  sensory  filaments  by  inoscula- 
tion with  other  nerves.  The  same  is  the  case,  also,  with  the  Motor 
.Nerves  of  the  Orbit  (the  6th,  4th,  and  3d,  of  Willis),  which  arise  by 
single  roots,  and  which  have  no  sensory  endowments  but  those  which 
they  obtain  by  inosculation  with  the  Fifth  pair. — On  the  other  hand, 
the  Fifth  pair  arises  by  a  double  root ;  that  which  corresponds  to  the 
anterior  or  motor  root  of  the  spinal  nerves  is  very  small,  however,  and 
only  enters  the  third  division  of  the  nerve,  which  supplies  the  muscles 
concerned  in  mastication ;  the  other  root,  corresponding  with  the  pos- 
terior roots  of  the  spinal  nerves,  is  of  large  size,  and  its  branches  are 
distributed  to  the  face  and  head,  endowing  them  with  sensibility.  Thus 
the  sensory  division  of  the  fifth  pair,  being  distributed,  not  merely  to 
the  same  parts  with  its  motor  division,  but  also  to  the  parts  which  de- 
rive their  motor  endowments  from  the  Facial  nerve,  and  from  the 
nerves  of  the  orbit,  may  be  regarded  as  making  up,  together  with  all  of 
them,  one  ordinary  Spinal  nerve. 

4.  Functions  of  the  Medulla  Oblongata. 

889.  This  portion  of  the  nervous  centres,  as  already  stated,  does  not 
difier  in  any  essential  particular  from  the  Spinal  Cord,  of  which  it  may 
be  considered  as  a  cranial  prolongation.  But  the  arrangement  of  its 
constituent  parts  is  peculiar ;  for  whilst  it  is  the  medium  by  which  the 
various  strands  of  the  Spinal  Cord  are  connected  with  the  different 
portions  of  the  Encephalon,  it  is  also  remarkable  as  being  the  gan- 
glionic centre,  concerned  in  the  maintenance  of  the  action  of  respi- 
ration, and  in  the  ingestion  of  food.  Four  principal  strands  of  nervous 
matter  may  be  distinguished  anatomically,  in  each  of  its  lateral  halves ; 
these  are,  anteriorly,  the  Anterior  Pyramids;  next,  the  Olivary 
bodies ;  next  the  Bestiform  bodies ;  and  lastly,  the  Posterior  Pyramids, 
It  will  be  presently  seen,  however,  that  the  physiological  relations  of 
these  strands,  as  indicated  by  their  connexions  with  the  Encephalon 
above,  with  the  Spinal  Cord  below,  and  with  the  nerves  that  have  their 
centres  in  them,  are  very  different  from  what  their  mere  relative  posi- 
tions would  indicate. — The  gray  or  vesicular  substance  in  this  part  no 
longer  holds  the  same  relation  to  the  white,  that  it  possesses  in  the 
Spmal  Cord ;  but  is  principally  aggregated  in  three  pairs  of  gangli- 
onic centres,  of  which  the  anterior  forms  the  nucleus  of  the  Olivary 
body,  the  lateral  of  the  Restiform,  and  the  posterior  of  the  Posterior 
Pyramidal. 

890.  The  Anterior  Pyramids  consist  entirely  of  fibrous  structure. 


STRUCTURE  OF  THE   MEDULLA  OBLONGATA.  505 

and  establish  a  communication  between  the  motor  tract  at  the  base  of 
the  Encephalon  (which  is  chiefly  derived  from  the  Corpora  Striata)  and 
the  anterior  and  antero-lateral  columns  of  the  Spinal  Cord.  They 
have  also  a  connexion  with  the  Cerebellum.  A  large  part  of  its  fibres 
decussate,  those  that  proceed  from  the  right  hemisphere  passing  into 
the  left  side  of  the  cord,  and  those  from  the  left  hemisphere  into  the 
right  side  of  the  cord ;  an  arrangment  which  fully  explains  the  fact, 
that  in  Hemiplegia,  the  paralytic  affection  of  the  body  is  on  the  side 
opposite  to  that  of  the  lesion  of  the  brain.  A  small  proportion  of  the 
fibres  of  the  anterior  pyramids  does  not  decussate;  and  this  passes 
down,  with  fibres  from  the  olivary  columns,  into  the  anterior  columns 
of  the  cord ;  whilst  the  decussating  fibres  dip  more  deeply  away  from 
the  anterior  surface  of  the  cord,  and  connect  themselves  rather  with  its 
lateral  or  middle  columns. 

891.  The  fibrous  portion  of  the  Olivary  hody  is  connected  above  with 
the  Motor  tract,  with  the  Corpora  Quadrigemina,  and  with  the  Cere- 
bellum, and  below  with  the  anterior  columns  of  the  Spinal  Cord. — The 
vesicular  nucleus  of  the  Olivary  body,  on  the  other  hand,  which  is 
known  as  the  corpus  dentatum,  seems  to  be  especially  connected  with 
the  origins  of  the  nerves  concerned  in  the  regulation  of  the  movements 
of  the  tongue ;  thus  we  find  that  anteriorly  a  portion  of  the  roots  of 
the  hypoglossal,  which  is  the  motor  nerve  of  the  tongue,  issue  from 
it ;  whilst  posteriorly,  a  portion  of  the  roots  of  the  glosso-pharyngeal, 
which  is  one  of  the  sensory  nerves  of  the  tongue,  seem  to  terminate 
in  it. 

892.  The  fibres  of  the  JRestiform  columns  are  continuous  above  with 
those  of  the  hemispheres  of  the  Cerebellum ;  and  below  they  pass, 
without  decussation,  chiefly  into  the  posterior  columns  of  the  Spinal 
Cord,  a  band  of  arciform  fibres,  however,  crossing  over  to  the  anterior 
and  lateral  columns  on  each  side.  The  ganglia  imbedded  in  these 
columns,  however,  seem  to  possess  a  completely  independent  function ; 
being  the  centres  of  the  Pneumogastric  nerves,  which  are  the  chief  ex- 
citers of  the  Respiratory  movements,  as  well  as  of  a  portion  of  the 
Glosso-pharyngeal  nerves. 

893.  The  Posterior  Pyramids  are  two  small  strands  of  fibrous  struc- 
ture, lying  between  the  two  restiform  bodies,  and  occupying  the  portion 
of  the  Medulla  Oblongata  on  either  side  of  the  posterior  median  furrow. 
They  may  be  traced  upwards  into  the  Thalamj  Optici,  and  downwards 
into  the  posterior  columns  and  the  posterior  part  of  the  lateral.  They 
undergo  a  decussation  in  their  upward  course ;  but  it  is  not  certain 
whether  this  decussation  involves  all  their  fibres. — The  gray  nuclei  of 
the  Posterior  Pyramids,  which  are  situated  immediately  beneath  the 
fourth  ventricle,  are  the  ganglionic  centres  of  the  Auditory  nerves,  or 
the  proper  Auditory  ganglia. 

894.  When  we  consider  these  various  lines  of  communication  simply 
in  their  Physiological  relations,  as  establishing  connexions  between  the 
Encephalon  above  and  the  Spinal  Cord  below,  it  will  be  convenient 
first  to  notice  and  put  aside  the  Cerebellar.  Of  these  there  are  two 
sets ;  the  principal  forming  the  Restiform  bodies,  which  connect  the 
Cerebellum  with  the  posterior  columns  of  the  Spinal  cord ;  whilst  there 


506  OF  THE  NERVOUS   SYSTEM  AND  ITS   ACTIONS. 

is  another  division,  which  comes  into  connexion  through  the  Olivary 
and  Pyramidal  bodies,  with  the  anterior  and  antero-lateral  columns. — 
The  remaining  fibres,  which  constitute  what  are  improperly  called  the 
Crura  Cerebri,  maj  be  considered  as  forming  two  principal  tracts,  the 
sensory  and  the  motor ;  these  being  distinguished  as  such  by  the  cha- 
racter of  the  nerves  which  arise  in  their  course.  The  sensory  tract 
passes  upwards  from  the  posterior  columns  of  the  Spinal  Cord,  and  the 
posterior  part  of  the  lateral,  to  the  Thalami  Optici ;  it  is  obviously  con- 
tinuous below  with  the  tract  in  which  the  posterior  roots  of  the  Spinal 
nerves  terminate,  and  in  its  upward  course  it  receives  the  large  or  sen- 
sory root  of  the  Fifth  pair ;  whilst  passing  through  the  Pons  Varolii,  it 
undergoes  a  partial  decussation.  On  the  other  hand,  the  motor  tract 
may  be  regarded  as  descending  from  the  Corpora  Striata  and-  Tuber- 
cula  Quadrigemina  into  the  anterior  and  antero-lateral  columns  of  the 
Spinal  Cord ;  in  its  course  it  gives  off  the  roots  of  all  the  motor  nerves 
usually  considered  as  cranial ;  and  the  greater  part  of  its  fibres  undergo 
decussation  below  the  Pons  Varolii. — The  functions  of  the  Medulla 
Oblongata  are,  therefore,  of  a  double  character ; — to  bring  the  higher 
parts  of  the  Encephalon  into  connexion  with  the  Spinal  Cord  and  the 
Nerves  that  issue  from  it ;  and  to  serve  as  a  centre  for  the  reflex 
movements,  performed  through  the  nerves  that  issue  from  it.  In  both 
respects  it  corresponds  precisely  with  any  segment  of  the  Spinal  Cord 
itself;  and  there  is  no  reason  to  believe,  that  it  possesses  any  other  or 
more  special  endowments.  The  importance,  however,  of  the  reflex  acts 
of  Respiration  and  Deglutition,  over  which  it  presides,  causes  this  por- 
tion of  the  Medulla  to  be  the  one,  whose  integrity  is  most  essential  to 
the  preservation  of  life ;  and  therefore  it  seems  to  possess  a  character 
more  distinctive  than  it  really  has. 

Fig.  154. 


Dissection  of  the  Medulla  Oblongata,  to  show  the  connexions  of  its  sereral  strands :— a.  corpus  striatum ; 
B,  thalamus  opticus;  c,  d,  corpora  quadrigemina;  e,  commissure  connecting  them  with  the  cerebellum;  F, 
corpora  restiformia;  p,  p,  pons  varolii;  st,  st,  sensory  tract;  mt,  mt,  motor  tract;  g,  olivary  tract;  j9,  pvra- 
midal  tract;  og,  oliyary  ganglion;  op,  optic  nerve;  3m,  root  of  the  third  pair  (motor);  6s,  sensory  root  of  the 

895.  The  chief  excitor  nerve  of  the  Respiratory  movements,  as  already 
stated  (§§  685-687)  is  the  aJ0Ferent  portions  of  the  Par  Vagum :  but  the 


STRUCTURE  AND  FUNCTIONS   OF   THE   MEDULLA  OBLONGATA.         507 

afferent  portion  of  the  Fifth  pair  is  also  a  powerful  excitor ;  and  the 
afferent  portions  of  all  the  spinal  nerves,  conveying  impressions  from 
the  general  surface  of  the  body,  are  also  capable  of  contributing  to  the 
excitement  necessary  for  the  production  of  the  movement. — The  chief 
motor  nerves  are  the  phrenic  and  intercostals ;  which,  though  issuing 
from  the  Cord  at  a  considerable  space  lower  down,  probably  originate 
in  the  Medulla  Oblongata.  The  motor  portions  of  several  other  spinal  • 
nerves  are  also  partly  concerned ;  as  are  also  the  Facial  nerve,  the 
motor  portion  of  the  Par  Yagum,  and  the  Spinal  Accessory.  The 
ordinary  movements  of  Respiration  involve  little  action  of  any  motor 
nerves  but  the  Phrenic  and  Intercostal ;  and  it  is  only  when  an  excess 
of  the  stimulus  (produced,  for  example,  by  too  long  a  suspension  of  the 
aerating  process)  excites  extraordinary  movements,  that  the  nerves  last 
enumerated  are  called  into  action. 

806.  The  acts  of  Prehension  of  food  with  lips,  and  of  Mastication^ 
though  usually  effected  by  voluntary  power  in  the  adult,  seem  to  be 
capable  of  taking  place  as  a  part  of  the  reflex  operation  of  the  Medulla 
Oblongata,  in  the  Infant,  as  in  the  lower  animals.  This  is  particularly 
evident  in  the  prehension  of  the  nipple  by  the  lips  of  the  infant,  and 
the  act  of  suction  which  the  contact  of  that  body  (or  of  any  resembling 
it)  seems  to  excite.  The  experiments  provided  for  us  by  nature,  in  the 
production  of  anencephalous  monstrosities,  fully  prove  that  the  integrity 
of  the  nervous  connexion  of  the  lips  and  respiratory  organs  with  the 
Medulla  Oblongata,  is  alone  sufiicient  for  the  performance  of  this  action ; 
and  experiments  upon  young  animals,  from  which  the  brain  has  been 
removed,  establish  the  same  fact.  Thus  Mr.  Grainger  found  that,  upon 
introducing  his  finger,  moistened  with  milk,  or  with  sugar  and  water, 
between  the  lips  of  a  puppy  thus  mutilated,  the  act  of  suction  was 
excited ;  and  not  merely  the  act  of  suction  itself,  but  other  movements 
having  a  relation  to  it ;  for  as  the  puppy  lay  on  its  side,  sucking  the 
finger,  it  pushed  out  its  feet,  in  the  same  manner  as  young  pigs  exert 
theirs  in  compressing  the  sow's  dugs.  This  action  seems  akin  to  many 
of  those,  by  which  the  lower  animals  take  in  their  food;  and  we  may 
thus  recognise  in  the  Medulla  Oblongata  a  distinct  centre  of  reflex 
action  for  the  reception  and  deglutition  of  aliment,  analogous  to  the 
stomato-gastric  ganglia  of  Invertebrated  animals. 

897.  In  the  movements  of  Deglutition,  which,  as  formerly  explained 
(§  453),  are  purely  reflex,  the  chief  excitor  is  undoubtedly  the  afferent 
portion  of  the  Glosso-pharyngeal  nerve.  It  is  found  that,  if  the  trunk  of 
this  nerve,  or  its  pharyngeal  (but  not  its  lingual)  branches,  be  pinched, 
pricked,  or  otherwise  irritated,  whilst  still  in  connexion  with  the  Medulla 
Oblongata,  the  movements  concerned  in  the  act  of  swallowing  are 
excited.  The  same  occurs  if,  when  the  trunk  of  the  Glosso-pharyn- 
geal has  been  divided,  the  cut  extremity  in  connexion  with  the  Medulla 
Oblongata  is  irritated;  but  little  or  no  muscular  contraction  is  produced 
by  irritation  of  the  separated  extremity ;  whence  it  is  apparent,  that 
the  Glosso-pharyngeal  has  little  or  no  direct  motor  power,  but  acts  as 
an  excitor.  In  this  it  appears  to  be  assisted  by  the  branches  of  the 
Fifth  pair  distributed  upon  the  fauces;  and  probably,  also,  by  the 
branches  of  the  superior  laryngeal  distributed  upon  the  Pharynx.     The 


508  OF  THE  NERVOUS  SYSTEM  AND   ITS  ACTIONS. 

motor  influence,  which  is  generated  in  respondence  to  the  stimulus  thus 
conveyed,  appears  to  act  chiefly  through  the  branches  of  the  Par  Yagum, 
which  are  distributed  to  most  of  the  muscles  concerned  in  swallowing ; 
but  the  Facial,  the  Hypoglossal,  the  motor  portion  of  the  Fifth,  and 
perhaps  also  the  motor  portions  of  some  of  the  Cervical  nerves,  are  also 
concerned  in  the  movement,  and  may  effect  it,  though  with  difiiculty, 
after  the  pharyngeal  branches  of  the  Par  Vagum  have  been  divided. 

898.  In  the  propulsion  of  the  food  down  the  (Esophagus,  to  which 
the  glosso-pharyngeal  nerve  does  not  extend,  the  muscular  contraction, 
so  far  as  it  is  of  a  reflex  nature  (§  455),  must  depend  upon  the  oesopha- 
geal branches  of  the  Par  Yagum  alone  ;  their  afferent  portion  being 
the  exciter,  and  their  motor  portion  giving  the  requisite  stimulus  to  the 
muscles.  The  same  must  be  the  case  in  regard  to  the  muscular  contrac- 
tions of  the  cardiac  and  pyloric  sphincters,  and  of  the  walls  of  the  sto- 
mach, so  far  as  regards  their  dependence  upon  the  nervous  system  at 
all ;  but  the  degree  of  this  is  doubtful. 

899.  There  are  other  reflex  actions  of  the  Medulla  Oblongata,  con- 
nected with  the  regulation  of  the  aperture  of  the  Glottis ;  these,  which 
are  effected  through  the  superior  and  inferior  laryngeal  branches  of  the 
Par  Yagum,  will  be  better  noticed,  when  the  actions  of  the  Larynx  are 
under  consideration  (§  976). — In  like  manner,  the  reflex  action  concerned 
in  the  regulation  of  the  aperture  of  the  Pupil,  will  be  more  conveniently 
noticed  in  the  sketch  to  be  hereafter  given  of  the  Physiology  of  Yision 
(§969). 

5.  Functions  of  the  Sensory  Ganglia. 

900.  All  the  nerves  of  Sensation,  both  general  and  special,  may  be 
traced  into  a  series  of  ganglionic  masses  lying  at  the  base  of  the  brain  ; 
which  seem  to  constitute  their  own  particular  centres.  Thus  we  have 
seen  in  Fishes,  the  Olfactive,  Optic,  and  Auditory  ganglia,  marked  out 
as  such,  by  the  termination  of  the  nerves  proceeding  from  the  organs  of 
smell,  sight,  and  hearing,  in  these  masses  respectively.  These  ganglia 
bear  an  evident  correspondence  with  the  cephalic  ganglia  of  the  Inverte- 
brata ;  which  must  chiefly,  however,  be  regarded  as  optic  ganglia,  since 
the  development  of  the  eyes  far  surpasses  that  of  the  other  organs  of 
special  sense.  On  the  other  hand,  they  find  their  representatives  in 
certain  organs  at  the  base  of  the  brain,  in  Man  and  the  higher  Mamma- 
lia ;  which,  though  small  in  proportion  to  the  whole  Encephalon,  are 
capable  of  being  clearly  marked  out  as  the  ganglionic  centres  of  the 
several  nerves  of  sense. — Thus,  anteriorly,  we  have  the  Olfactive  gan- 
glia, in  what  are  commonly  termed  the  bulbous  expansions  of  the  Olfac- 
tive nerve  ;  which,  however,  are  real  ganglia,  containing  gray  or  vesicular 
substanco  ;  and  their  separation  from  the  general  mass  of  the  Encepha- 
lon, by  the  peduncles  or  footstalks  commonly  termed  the  trunks  of  the 
olfactory  nerves,  finds  its  analogy  in  many  species  of  Fish  (§  869).  The 
ganglionic  nature  of  these  masses  is  more  evident  in  many  of  the  lower 
Mammalia,  in  which  the  organ  of  smell  is  highly  developed,  than  it  is 
in  Man,  whose  olfactive  powers  are  comparatively  moderate. — At  some 
distance  behind  these,  we  have  the  representatives  of  the  Optic  Ganglia, 


THALAMI  OPTICI,  AND  CORPOEA   STRIATA. 


609 


in  the  Tuhercula  Quadrigemina,  to  which  the  principal  part  of  the 
roots  of  the  Optic  nerve  may  be  traced.  Although  these  bodies  are  so 
small  in  Man,  as  to  be  apparently  insignificant,  yet  they  are  relatively 
larger,  and  form  a  more  evidently-important  part  of  the  Encephalon,  in 
many  of  the  lower  Mammalia ;  though  still  presenting  the  same  general 
aspect. — The  Auditory  ganglia  seldom  form  distinct  lobes  or  projec- 
tions ;  but  are  usually  lodged  in  the  substance  of  the  Medulla  Oblon- 
gata. Their  real  character  is  most  evident  in  certain  Fishes,  as  the 
Carp  ;  in  which  we  find  the  Auditory  Nerve  having  as  distinct  a  gan- 
glionic centre  as  the  Optic.  In  higher  animals,  however,  we  are  able  to 
trace  the  Auditory  nerve  into  a  small  mass  of  gray  matter,  which  lies 
on  each  side  of  the  Fourth  Ventricle ;  and  although  this  is  lodged  in 
the  midst  of  parts  whose  function  is  altogether  difi'erent,  yet  there  seems 
no  reason  for  doubting  that  it  has  a  character  of  its  own,  and  that  it  is 
really  the  ganglion  of  the  auditory  nerve. — We  are  not  able  to  fix  upon 
any  such  mass  of  gray  matter,  as  the  distinct  Gustatory  ganglion  ;  nor 

Fig.  155. 


Diagram  of  the  relation  of  the  Sensori-motor  tract  at  the  base  of  the  Brain,  to  the  Cerebrum,  as  seen  in 
horizontal  section : — olf,  olfactive  ganglia ;  opt,  optic  ganglia ;  aud,  auditory  ganglia ;  cs,  corpora  striata ; 
thai,  thalami  optici ;  a,  a,  olfactive  nerves ;  b,  b,  optic  nerves ;  c,  c,  auditory  nerves. 

is  it  necessary  to  attempt  to  do  so ;  for,  as  we  shall  see  hereafter,  there 
is  strong  reason  to  regard  the  sense  of  Taste  as  only  a  refined  kind  of 
Touch,  combined  with  the  sense  of  Smell. 

901.  At  the  base  of  the  Cerebral  Hemispheres,  we  find  two  gan- 
glionic masses  on  either  side ;  through  which  all  the  fibres  pass  that 
connect  the  Hemispheres  with  the  Medulla  Oblongata.  These  are  the 
Corpora  Striata^  and  Thalami  OjJtici.  Upon  tracing  forwards  the 
tract  of  motor  fibres  that  ascend  from  the  Anterior  Pyramids,  we  find 
it  passing  chiefly  into  the  Corpora  Striata;  whilst  if  we  follow  the 


510  OF  THE  NERVOUS  SYSTEM  AND  ITS  ACTIONS. 

Sensory  Column  that  ascends  from  the  Posterior  Pyramids,  we  shall 
find  it  to  enter  the  Thalami  Optici.  These  bodies  have  been  usually 
considered  as  mere  appendages  to  the  Cerebrum  ;  but  the  fact  that  they 
are  independent  centres  of  action  is  fully  established  by  the  presence  of 
a  large  quantity  of  vesicular  matter  in  their  substance ;  and  there  is 
now  a  sufficiently  large  amount  of  evidence,  both  anatomical  and  physio- 
logical, to  render  it  probable  that  the  fibres  which  seem  to  pass  through 
them  from  the  Crura  Cerebri,  and  then  to  radiate  towards  the  periphery 
of  the  Cerebral  Hemispheres,  do  not  do  so  in  reality,  but  that  these 
ganglionic  masses  receive,  on  the  one  hand,  the  fibres  that  ascend  to 
them  from  the  Medulla  Oblongata,  and,  on  the  other,  are  the  point  of 
departure  of  a  new  set,  passing  to  the  proper  Cerebrum.  Looking  to 
the  connexion  of  the  Thalami  Optici  with  the  sensory  tract,  it  may  be 
regarded  as  not  improbable  that  we  may  consider  them  as  the  ganglionic 
centres  of  common  sensation ;  standing  in  the  same  relation  to  the  sen- 
sory nerves,  that  converge  from  various  parts  of  the  body  towards  the 
Encephalon,  as  do  the  Optic  and  other  ganglia  to  their  nerves  of  special 
sensation.  And  as  these  last  give  origin  to  motor  fibres,  so  may  we 
regard  the  ganglionic  matter  of  the  Corpora  Striata  (which  are  in  close 
connexion  with  the  Thalami)  as  probably  sharing  in  the  same  function ; 
giving  origin  to  the  motor  fibres,  which  produce  the  respondent  con- 
sensual movements ;  just  as  the  anterior  peak  of  gray  matter  in  the 
Spinal  Cord  gives  exit  to  the  motor  filaments,  which  efi'ect  the  reflex 
movements  excited  through  the  afi"erent  fibres  forming  part  of  the  pos- 
terior roots. 

902.  The  functions  of  this  series  of  ganglia  may  be  more  certainly 
determined  by  the  aid  of  Comparative  Anatomy,  than  by  experimental 
mutilations.  Reverting  to  the  class  of  Fishes,  we  find  that  it  there 
constitutes,  with  the  Cerebellum,  nearly  the  entire  Encephalon  ;  scarcely 
a  rudiment  of  the  true  Cerebrum  being  discoverable  in  that  group.* 
And  when  we  descend  to  the  Invertebrata,  we  find  the  Cephalic  masses 
entirely  to  consist  of  the  ganglionic  centres  of  the  nerves  of  sense  and . 
motion.  There  can  scarcely  be  a  reasonable  doubt,  that  these  Cephalic 
ganglia  are  the  seat  of  consciousness  and  the  sources  of  those  movements 
which  are  directed  by  sensation,  in  such  animals  as  present  this  low 
type  of  nervous  organization ;  and  there  is  no  adequate  reason  for  the 
belief  that  the  superaddition  of  the  Cerebral  Hemispheres  in  the  Verte- 
brated  series  alters  the  endowments  of  the.  Sensory  Ganglia  on  which 
they  are  superimposed ;  on  the  contrary,  we  everywhere  see  that  the 
addition  of  new  ganglionic  centres,  as  instruments  of  new  functions, 
leaves  those  which  were  previously  existing  in  the  discharge  of  their 
original  duties.  Hence  we  should  be  led  to  regard  them  as  the  centres 
of  consciousness,  even  in  Man,  each  pair  of  ganglionic  centres  minister- 
ing to  that  peculiar  kind  of  sensation  for  which  its  nerves  and  the  organs 
they  supply  are  set  apart ;  thus  we  should  consider  the  Optic  ganglia  to 
be  the  seat  of  Visual  sensations,  the  Auditory  to  be  the  seat  of  the  sense 
of  hearing,  and  so  on.     And  we  should  also  consider  them  as  the  instru- 

*  The  ganglionic  masses,  commonly  designated  as  the  Cerebral  lobes  or  hemispheres, 
must  be  really  likened  in  great  part  (as  already  stated  I  869)  to  the  Corpora  Striata. 


FUNCTIONS   OF  THE   SENSORY  GANGLIA.  511 

ments  whereby  sensations,  of  whatever  kind,  either  originate  or  direct 
Automatic  movements. 

903.  So  far  as  the  results  of  experiments  can  be  relied  on,  they 
afford  a  confirmation  of  these  views,  by  showing  that  sensory  impressions 
can  be  felt,  and  that  automatic  movements  of  a  higher  kind  than  the 
simply  reflex  can  be  called  into  play  after  the  removal  of  the  Cerebral 
Hemispheres,  provided  that  these  ganglia  be  left  intact.  Thus,  if  a 
Bird  be  thus  mutilated,  it  maintains  its  equilibrium,  and  recovers  it 
when  it  has  been  disturbed  ;  if  pushed,  it  walks  ;  if  thrown  into  the  air, 
it  flies.  A  pigeon  deprived  of  its  cerebrum  has  been  observed  to  seek 
out  the  light  parts  of  a  partially-illuminated  room  in  which  it  was  con- 
fined, and  to  avoid  objects  that  lay  in  its  way;  and  at  night,  when 
sleeping  with  closed  eyes  and  its  head  under  its  wing,  it  raised  its  head 
and  opened  its  eyes  upon  the  slightest  noise.  So,  again,  the  removal 
or  destruction  of  one  pair  of  these  Sensory  centres  appears  to  involve 
the  loss  of  the  particular  sense  to  which  it  ministers ;  and  frequently, 
also,  to  occasion  such  a  disturbance  in  the  ordinary  movements  of  the 
animal,  as  to  show  the  importance  of  these  centres  in  regulating  them. 
Such  experiments  have  been  chiefly  made  upon  the  Optic  ganglia,  or 
Corpora  Quadrigemina,  the  partial  loss  of  which  on  one  side  produces 
temporary  blindness  in  the  eye  of  the  opposite  side,  and  partial  loss  of 
muscular  power  on  the  opposite  side  of  the  body ;  and  the  removal  of  a 
larger  portion,  or  the  complete  extirpation  of  it,  occasions  permanent 
blindness  and  immobility  of  the  pupil,  and  temporary  muscular  weak- 
ness, on  the  opposite  side.  This  temporary  disorder  of  the  muscular 
system  sometimes  manifests  itself  in  a  tendency  to  move  on  the  axis,  as 
if  the  animal  were  giddy ;  and  sometimes  in  irregular  convulsive  move- 
ments. Here,  then,  we  have  proof  of  the  necessity  of  the  integrity  of 
this  ganglionic  centre  for  the  possession  of  the  sense  of  vision ;  and  we 
have  further  proof  that  the  ganglion  is  connected  with  the  muscular 
apparatus,  by  motor  nerves  issuing  from  it.  The  reason  w^hy  the  eye 
of  the  opposite,  side  is  affected  is  to  be  found  in  the  decussation  of  the 
optic  nerves,  a  point  to  be  immediately  adverted  to  (§  907).  The 
influence  of  the  operation  on  the  muscles  of  the  opposite  side  of  the  body 
is  at  once  understood  from  the  fact  of  the  decussation  of  the  motor 
fibres  in  the  anterior  pyramids  (§  890).  Similar  disturbances  of  move- 
ment have  been  produced  by  injuries  to  the  organs  of  sense  themselves, 
or  to  the  nerves  connecting  them  with  the  sensorial  centres.  Thus,  if 
one  of  the  eyes  of  a  pigeon  be  blindfolded,  or  its  humours  be  evacuated, 
vertiginous  motions  ensue ;  and  section  of  one  of  the  semicircular  canals 
of  the  ear  in  pigeons  and  rabbits  has  been  found  to  occasion  constant 
efforts  to  move  in  the  plane  of  that  canal,  thus  confirming  the  belief 
that  the  function  of  these  canals  is  to  indicate  the  direction  of  sounds 
(§  952). 

904.  Notwithstanding  that,  in  Man,  the  high  development  of  Intel- 
ligence^ and  the  exercise  of  the  Will,  supersede  in  great  degree  the 
operations  of  Instinct,  we  still  find  that  there  are  in  ourselves  certain 
movements  which  can  be  distinguished  as  neither  voluntary  nor  simply 
reflex,  and  which  are  examples  of  the  method  of  operation  that  seems  to 
be  the  chief  source  of  the  actions  of  the  lower  Yertebrata,  as  of  the 


512  OF   THE   NERVOUS   SYSTEM  AND   ITS   ACTIONS. 

Invertebrated  classes  in  general.  These  movements  are  as  automatic 
and  involuntary  as  are  the  ordinary  reflex  actions,  but  differ  from  them 
in  requiring  that  the  impressions  which  originate  them  should  be  felt  as 
sensations ;  and  hence  they  are  conveniently  designated  as  consensual 
As  examples  of  this  group,  we  may  advert  to  the  start  upon  a  loud  and 
unexpected  sound ;  the  sudden  closure  of  the  eyes  to  a  dazzling  light, 
or  on  the  approach  of  bodies  that  might  injure  them,  which  has  been 
observed  to  take  place  even  in  cases  in  which  the  eyelids  could  not  be 
voluntarily  closed;  the  act  of  sneezing  excited  by  an  irritation  of  the 
nostril,  and  sometimes  also  by  a  dazzling  light;  the  semi-convulsive 
movements  and  the  laughter  called  forth  by  tickling ;  and  the  vomiting 
occasioned  by  the  sight  or  the  smell  of  a  loathsome  object.  So,  again, 
the  act  of  yawning  is  ordinarily  called  forth  by  certain  uneasy  sensa- 
tions within  ourselves,  but  also  by  the  sight  or  hearing  of  the  act  as 
performed  by  another.  Various  phenomena  of  disease  exhibit  the 
powerful  influence  of  sensations  in  producing  automatic  motions.  As 
instances  of  this  kind,  we  may  refer  to  the  eff*ects  of  the  sight  or  the 
sound  of  liquids,  or  of  the  slightest  currents  of  air,  in  exciting  the 
Hydrophobic  paroxysm ;  whilst  in  many  Hysteric  subjects  the  sight  of 
a  paroxysm  in  another  individual  is  the  most  certain  means  of  its  induc- 
tion in  themselves.  The  most  remarkable  examples,  however,  of  auto- 
matic movements  depending  upon  sensations,  are  those  which  we  come 
to  perform  habitually,  and,  as  we  commonly  say,  mechanically,  when 
the  attention  and  the  voluntary  efi'ort  are  directed  in  quite  a  difierent 
channel.  Thus  the  man  who  is  walking  through  the  streets  in  a  com- 
plete reverie,  unravelling  some  knotty  subject,  or  working  out  a  mathe- 
matical problem,  not  only  performs  the  movements  of  progression,  which 
may  be  simply  reflex)  with  great  regularity,  but  also  directs  these  in  a 
manner  which  plainly  indicates  the  guidance  of  sensations.  Thus,  he 
will  avoid  obstacles  in  the  line  of  his  path,  and  he  will  follow  the  course 
which  he  has  been  accustomed  to  take,  although  he  may  have  intended 
to  pass  along  some  very  different  route ;  and  it  is  not  until  his  attention 
is  recalled  to  his  situation,  that  his  train  of  thought  suffers  the  least 
intermission,  or  that  his  will  is  brought  to  bear  upon  his  motions. 

905.  We  may  trace  the  agency  of  the  Sensory  Ganglia,  however,  in 
the  Human  subject,  not  merely  in  their  direct  and  independent  opera- 
tion upon  the  muscular  system,  but  also  in  the  manner  in  which  they 
participate  in  all  Voluntary  actions.  The  existence  of  a  Sensation  of 
some  kind,  in  connexion  with  a  Muscular  exertion,  seems  essential  to 
the  continuance  of  the  latter.  Our  ordinary  movements  are  guided  by 
what  is  termed  the  Muscular  Sense;  that  is,  by  a  feeling  of  the  con- 
dition of  the  muscle,  that  comes  to  us  through  its  own  sensory  nerves. 
How  necessary  this  is  to  the  exercise  of  muscular  power  may  be  best 
judged  of  from  cases  in  which  it  has  been  lost.  Thus,  a  woman  who 
had  suffered  complete  loss  of  sensation  in  one  arm,  but  who  retained  its 
motor  power,  found  that  she  could  not  support  her  infant  upon  it, 
without  constantly  looking  at  the  child ;  and  that,  if  she  were  to  remove 
her  eyes  for  a  moment,  the  child  would  fall,  in  spite  of  her  knowledge 
that  her  infant  was  resting  upon  her  arm,  and  of  her  desire  to  sustain 
it.     Here,  the  muscular  sense  being  entirely  deficient,  the  sense  of 


DECUSSATION  OF  THE   OPTIC  NERVE.  513 

vision  supplied  what  was  required,  so  long  as  it  was  exercised  upon  the 
object ;  but  as  soon  as  this  guiding  influence  was  withdrawn,  the  strong- 
est will  could  not  sustain  the  muscular  contraction.  Again,  in  the 
production  of  vocal  sounds,  the  nice  adjustment  of  the  muscles  of  the 
larynx,  which  is  requisite  to  produce  determinate  tones,  can  only~be~ 
effected  in  obedience  to  a  mental  conception  of  the  tone  to  be  uttered ; 
and  this  conception  cannot  be  formed,  unless  the  sense  of  hearing  has 
previously  brought  similar  tones  to  the  mind.  Hence  it  is  that  persons 
who  are  born  deaf  are  also  dumb.  They  may  have  no  malformation  of 
the  organs  of  speech ;  but  they  are  incapable  of  uttering  distinct  vocal 
sounds  or  musical  tones,  because  they  have  not  the  guiding  conception, 
or  recalled  sensation,  of  the  nature  of  these.  By  long  training,  and  by 
efforts  directed  by  the  muscular  sense  of  the  larynx  itself,  some  persons 
thus  circumstanced  have  acquired  the  power  of  speech ;  but  the  want  of 
sufficiently  definite  control  over  the  vocal  muscles  is  always  very  evident 
in  their  use  of  the  organ. 

906.  Quitting  now  the  functions  of  the  Sensory  Ganglia,  we  have 
briefly  to  notice  certain  peculiarities  in  the  characters  of  the  Nerves  to 
which  they  serve  as  the  centres.  And  of  these  peculiarities,  there  is 
one  of  a  very  remarkable  nature,  which  is  common  to  the  three  nerves 
of  special  sense, — namely,' the  Olfactive,  Optic,  and  Auditory; — that 
they  are  not  in  the  least  degree  endowed  with  common  sensibility ;  so 
that  they  may  be  cut,  stretched,  pinched,  &c.,  without  producing  the 
least  pain.  Consequently,  the  ordinary  sensibility  of  the  surfaces  they 
supply  is  entirely  due  to  the  branches  of  the  Fifth  pair,  which  are  dis- 
tributed upon  them  ;  and  we  may  have  a  loss  of  either  the  general  or 
special  sensibility  of  any  of  the  organs  of  sense,  without  the  other  being 
affected,  save  indirectly.  Again,  we  do  not  find  that  irritation  of  these 
nerves  produces  any  other  purely  reflex  movements,  than  such  as  are 
connected  with  the  operations  of  the  organs  of  sense,  in  which  they 
respectively  originate.  Thus  the  Olfactory  nerve  cannot,  by  any  irrita- 
tion, be  made  to  excite  a  reflex  movement ;  the  only  reflex  action  that 
can  be  excited  by  irritating  the  Optic  nerve,  is  contraction  of  the 
Pupil ;  and  the  regulation  of  the  tension  of  the  Membrana  Tympani  (if, 
as  is  probable,  this  is  effected  by  the  motor  power  of  the  Facial  nerve, 
excited  by  impressions  made  upon  the  organ  of  sense),  appears  to  be 
the  only  reflex  action  to  which  the  Auditory  nerve  can  minister. 

907.  There  is  a  further  peculiarity,  of  a  very  marked  kind,  attend- 
ing the  course  of  the  Optic  nerves ;  this  is  the  crossing  or  decussation 
which  they  undergo,  more  or  less  completely,  whilst  proceeding  from 
their  ganglia  to  the  eyes.  In  some  of  the  lower  animals,  in  which  the 
two  eyes  (from  their  lateral  position)  have  entirely  different  spheres  of 
vision,  the  decussation  is  complete ;  the  whole  of  the  fibres  from  the 
right  Optic  ganglion  passing  into  the  left  eye,  and  vice  versd.  This  is 
the  case,  for  example,  with  most  of  the  Osseous  Fishes  (as  the  cod, 
halibut,  &c.) ;  and  also,  in  great  part  at  least,  with  Birds.  In  the 
Human  subject,  however,  and  in  animals  which,  like  him,  have  the  two 
eyes  looking  in  the  same  direction,  the  decussation  seems  less  complete ; 
but  there  is  a  very  remarkable  arrangement  of  the  fibres,  which  seems 
destined  to  bring  the  two  eyes  into  peculiarly  consentaneous  action. 

33 


514  OF  THE  NERVOUS  System  and  its  actions. 

The  posterior  border  of  the  Optic  Chiasma  is  formed  exclusively  of  com- 
missural fibres,  which  pass  from  one  optic  ganglion  to  the  other,  with- 
out entering  the  real  optic  nerve.  Again,  the  anterior  border  of  the 
chiasma  is  composed  of  fibres,  which  seem,  in  like  manner,  to  act  as  a 
commissure  between  the  two  retince ;  passing  from  one  to  the  other, 
without  any  connexion  with  the  optic  ganglia.  The  tract  which  lies 
between  the  two  borders,  and  occupies  the  middle  of  the  chiasma,  is 
the  true  optic  nerve  ;  and  in  this  it  would  appear  that  a  portion  of  the 
fibres  decussates,  whilst  another  portion  passes  directly  from  each  Op- 
tic ganglion  into  the  corresponding  eye.  The  fibres  which  proceed  from 
the  ganglia  to  the  retinae,  and  constitute  the  proper  optic  nerves,  may 
be  distinguished  into  an  internal  and  external  tract.  Of  these,  the 
external,  on  each  side,  passes  directly  onwards  to  the  eye  of  that  side ; 
whilst  the  internal  crosses  over  to  the  eye  of  the  opposite  side.  The  dis- 
tribution of  these  two  sets  of  fibres  in  the  retina  of  each  side  respectively, 
is  such  that,  according  to  Mr.  Mayo,  the  fibres  from  either  optic  gan- 
glion will  be  distributed  to  its  own  side  of  both  eyes  ; — the  right  optic 
ganglion  being  thus  exclusively  connected  with  the  outer  part  of  the 
retina  of  the  right  eye,  and  with  the  inner  part  of  the  retina  of  the  left 
eye;  and  the  left  optic  ganglion  being,  in  like  manner,  connected  ex- 
clusively with  the  outer  side  of  the  left  retina,  and  with  the  inner  side 
of  the  right.  Now  as  either  side  of  the  eye  receives  the  images  of 
objects,  which  are  on  the  other  side  of  its  axis,  it  follows,  if  this  account 
of  their  distribution  be  correct,  that  in  Man,  as  in  the  lower  animals, 
each  ganglion  receives  the  sensations  of  objects  situated  on  the  opposite 
sides  of  the  body.  The  purpose  of  this  decussation  may  be,  to  bring 
the  visual  impressions,  which  are  so  important  in  directing  the  move- 
ments of  the  body,  into  proper  harmony  with  the  motor  apparatus  ;  so 
that,  the  decussation  of  the  motor  fibres  in  the  pyramids  being  accom- 
panied by  a  decussation  of  the  optic  nerves,  the  same  efi'ect  is  produced 
as  if  neither  decussated, — which  last  is  the  case  with  Invertebrated 
animals  in  general. 

6.  Functions  of  the  Cerebellum.  ^ 

908.  Much  discussion  has  taken  place,  of  late  years,  respecting  the 
uses  of  the  Cerebellum;  and  many  experiments  have  been  made  to 
determine  them.  That  it  is  in  some  way  connected  with  the  powers  of 
motion,  might  be  inferred  from  its  connexion  with  the  antero-lateral 
columns  of  the  Spinal  Cord,  as  well  as  with  the  posterior ;  and  the  com- 
parative size  of  the  organ,  in  dilBferent  orders  of  Vertebrated  animals, 
gives  us  some  indication  of  what  the  nature  of  its  function  may  be.  For 
we  find  its  degree  of  development  corresponding  pretty  closely  with  the 
variety  and  energy  of  the  muscular  movements  which  are  habitually  exe- 
cuted by  the  species ;  the  organ  being  the  largest  in  those  animals  which 
require  the  combi7ied  effort  of  a  great  variety  of  muscles  to  maintain  their 
usual  position,  or  to  execute  their  ordinary  movements  ;  whilst  it  is  the 
smallest  in  those  which  require  no  muscular  exertion  for  the  one  pur- 
pose, and  little  combination  of  different  actions  for  the  other.  Thus, 
in  animals  that  habitually  rest  and  move  upon  four  legs,  there  is  com- 


FUNCTIONS   OF  THE   CEREBELLUM.  616 

paratively  little  occasion  for  any  organ  to  combine  and  harmonize 
the  actions  of  their  several  muscles ;  and  in  these,  the  Cerebellum  is 
usually  small.  But  among  the  more  active  predaceous  Fishes  (as  the 
Shark),  Birds  of  the  most  powerful  and  varied  flight  (as  the  Swallow), 
and  such  Mammals  as  can  maintain  the  erect  position,  and  can  use  their 
extremities  for  other  purposes  than  support  and  motion, — we  find  the 
Cerebellum  of  much  greater  size,  relatively  to  the  remainder  of  the 
Encephalon.  There  is  a  marked  advance  in  this  respect,  as  we  ascend 
through  the  series  of  Quadrumanous  animals ;  from  the  Baboons,  which 
usually  walk  on  all-fours,  to  the  semi-erect  Apes,  which  often  stand  and 
move  on  their  hind-legs  only.  The  greatest  development  of  the  Cere- 
bellum is  found  in  Man  ;  who  surpasses  all  other  animals  in  the  number 
and  variety  of  the  combinations  of  muscular  movement  which  his  ordi- 
nary actions  involve,  as  well  as  of  those  which  he  is  capable,  by  prac- 
tice, of  learning  to  execute. 

909.  From  experiments  upon  all  classes  of  Vertebrated  animals,  it 
has  been  found  that,  when  the  Cerebellum  is  removed,  the  power  of 
walking,  springing,  flying,  standing,  or  maintaining  the  equilibrium  of 
the  body,  is  destroyed.  It  does  not  seem  that  the  animal  has  in  any 
degree  lost  the  voluntary  power  over  its  individual  muscles  ;  but  it  can- 
not combine  their  actions  for  any  general  movements  of  the  body.  The 
reflex  movements,  such  as  those  of  respiration,  remain  unimpaired. 
When  an  animal  thus  mutilated  is  laid  on  its  back,  it  cannot  recover  its 
former  posture ;  but  it  moves  its  limbs,  or  flutters  its  wings,  and  evi- 
dently is  not  in  a  state  of  stupor.  When  placed  in  the  erect  position, 
it  staggers  and  falls  like  a  drunken  man ;  not,  however,  without  making 
efibrts  to  maintain  its  balance.  Phrenologists,  who  attribute  a  difi'erent 
function  to  the  Cerebellum,  have  attempted  to  put  aside  these  results, 
on  the  ground  that  the  severity  of  the  operation  is  alone  sufficient  to 
produce  them ;  but,  as  we  shall  presently  see,  many  animals  may  be 
subjected  to  a  much  more  severe  operation,  the  removal  of  the  Cerebral 
hemispheres,  without  the  loss  of  the  power  of  combining  and  harmoniz- 
ing the  muscular  actions,  provided  the  Cerebellum  be  left  uninjured. 
Thus,  then,  the  idea  of  the  functions  of  the  Cerebellum,  which  we  derive 
from  Comparative  Anatomy,  seems  fully  borne  out  by  the  results  of  ex- 
periment ;  and  it  is  also  consistent  with  the  indications  which  may  be 
drawn  from  the  observations  of  Pathological  phenomena.  When  the  Ce- 
rebellum is  affected  with  chronic  disease,  the  ^otor  function  is  seldom 
destroyed ;  but  the  same  kind  of  want  of  combining  power  shows  itself, 
as  when  the  organ  has  been  purposely  mutilated.  Some  kind  of  lesion 
of  the  motor  function  is  invariably  to  be  observed ;  whilst  the  mental 
powers  may  or  may  not  be  affected, — probably  according  to  the  influ- 
ence of  the  disease  in  the  Cerebellum,  upon  other  parts.  The  same 
absence  of  any  direct  connexion  with  the  Psychical  powers,  is  shown  in 
the  fact,  that  inflammation  of  the  membranes  covering  it,  if  confined  to 
the  Cerebellum,  does  not  produce  delirium.  Sudden  effusions  of  blood 
into  its  substance  may  produce  apoplexy  or  paralysis ;  but  this  may 
occur  as  a  consequence  of  effusions  into  any  part  of  the  Encephalon, 
and  does  not  indicate  that  the  Cerebellum  has  anything  to  do  with  the 
mental  functions,  or  with  the  power  of  the  Will  over  the  muscles. 


516  OF  THE  NERVOUS   SYSTEM  AND  ITS  ACTIONS. 

910.  There  is  another  doctrine,  however,  in  regard  to  the  functions 
of  the  Cerebellum,  first  propounded  by  Gall ;  which  ought  not  to  be 
altogether  passed  by.  According  to  the  system  of  Phrenologists,  the 
Cerebellum  is  the  organ  of  the  sexual  instinct ;  and  its  connexion  with 
the  motor  function  is  limited  to  the  performance  of  the  movements,  to 
which  that  instinct  leads.  This  doctrine  derives  no  support,  however, 
from  the  facts  supplied  by  Comparative  Anatomy  ;  for  there  is  a  com- 
plete want  of  correspondence  between  the  size  of  the  Cerebellum  in 
different  animals,  and  the  power  of  their  sexual  instinct. — Again, 
although  Pathology  has  been  appealed  to,  as  showing  a  decided  con- 
nexion between  disease  of  the  Cerebellum  and  afi"ection  of  the  Genital 
organs  (manifesting  itself  in  priapism,  turgescence  of  the  testes,  seminal 
emissions,  &c.),  yet  it  appears,  on  a  careful  examination  of  evidence, 
that  such  a  sympathy  is  comparatively  rare,  not  being  displayed  in 
more  than  one  out  of  every  seventeen  cases  of  Cerebellic  disease.  And 
where  it  is  manifested,  it  is  explicable  quite  readily  by  the  known  fact, 
that  this  kind  of  excitement  of  the  genital  organs  may  be  produced  by 
excitement  of  the  spinal  cord  and  medulla  oblongata. — Little  or  no 
light  has  been  thrown  on  this  question  by  experiment.  It  was  asserted 
by  Gall,  that  the  Cerebellum  is  very  small  in  castrated  animals  ;  but 
this  assertion  has  been  met  by  the  most  positive  counter-statements  on 
the  part  of  Leuret,  who  has  shown  that  the  average  weight  of  the  Cere- 
bellum (both  absolutely,  and  in  proportion  to  the  weight  of  the  entire 
encephalon)  is  even  greater  in  Geldings,  than  in  Stallions  or  Mares. — It 
is  asserted,  however,  that  the  results  of  observation  in  Man  lead  to  a 
positive  conclusion,  that  the  size  of  the  Cerebellum  is  a  measure  of 
the  intensity  of  the  sexual  instinct  in  the  individual.  This  assertion 
has  been  met  by  the  counter-statement  of  others,  that  no  such  relation 
exists.  There  are,  of  course,  very  great  difficulties  in  regard  to  the 
collection  of  accurate  information  on  this  subject ;  and  the  question 
must  be  at  present  regarded  as  sub  judice. 

911.  It  may  be  added,  that  the  idea  of  a  special  connexion  between 
the  sexual  instinct  and  the  Cerebellum,  is  not  inconsistent  with  the  view 
of  its  function  previously  stated ;  and  it  would  seem  to  derive  some 
confirmation  from  the  fact,  that  an  unusual  amount  of  muscular  exer- 
tion appears  to  have  a  peculiar  tendency  to  depress  the  sexual  passion, 
even  whilst  it  increases  the  general  vigour  of  the  system.  If  the  Cere- 
bellum be  really  connected  with  both  kinds  of  functions,  it  does  not 
seem  unlikely  that  the  excessive  employment  of  it  upon  one,  should 
diminish  its  energy  in  regard  to  the  other.  Further,  it  seems  not 
improbable,  that  the  Lobes  of  the  Cerebellum  are  the  parts  specially 
concerned  in  the  regulation  of  the  muscular  movements ;  whilst  the 
central  portion  (constituting  the  Vermiform  process  in  Man,  but  form- 
ing the  entire  cerebellum  of  many  of  the  lower  Vertebrata,  such  as  the 
-Prog)  may  contain  the  centre  of  the  sexual  sensations,  and  may  thus  be 
the  instrument  of  the  consensual  actions  to  which  they  give  rise. 

7.  Functions  of  the  Cerebrum. 

912.  The  view  which  has  been  taken  of  the  Comparative  structure  of 
iJie  Nervous  system,  in  different  animals,  leads  to  the  conclusion,  that 


RELATIVE  DEVELOPMENT  OF  THE  CEREBRUM.        517 

the  Cerebral  Hemispheres  are  far  from  being  the  essential  parts  of  the 
apparatus  they  were  formerly  imagined  to  be  ;  and  that  they  are,  on 
the  contrary,  superadded  organs,  of  which  we  find  no  distinct  represen- 
tatives in  the  Invertebrata,  and  of  which  the  first  appearance  (in  the 
class  of  Fishes)  exhibits  them  in  the  light  of  appendages,  destined  to 
perform  some  special  function  peculiar  to  Vertebrated  animals.  The 
results  of  the  removal  of  the  Cerebral  Hemispheres,  in  animals  to  which 
the  shock  of  the  operation  does  not  prove  immediately  fatal,  fully  con- 
firms this  view  ;  and  must  appear  extraordinary  to  those,  who  have 
been  accustomed  to  regard  these  organs  as  the  centre  of  all  energy. 
Not  only  Reptiles,  but  Birds  and  Mammalia,  if  their  physical  wants  be 
supplied,  may  survive  the  removal  of  the  whole  Cerebrum  for  weeks,  or 
even  months.  If  the  entire  mass  be  taken  away  at  once,  the  operation 
is  usually  fatal ;  but  if  it  be  removed  by  successive  slices,  the  shock  is 
less  severe,  and  the  depression  it  produces  in  the  organic  functions  is 
soon  recovered  from.  It  is  difiicult  to  substantiate  the  existence  of 
actual  sensation  in  animals  thus  circumstanced ;  but  their  movements 
appear  to  be  of  a  higher  kind,  as  already  remarked  (§  903),  than  those 
resulting  from  mere  reflex  action.  Thus  they  will  eat  food,  when  it  is 
put  into  their  mouths  ;  although  they  do  not  go  to  seek  it.  If  violently 
aroused,  the  animal  has  all  the  manner  of  one  waking  from  sleep ;  and 
it  manifests  about  the  same  degree  of  consciousness  as  a  sleeping 
Man,  whose  torpor  is  not  too  profound  to  prevent  his  sufi*ering  from  an 
uneasy  position,  and  who -moves  himself  to  amend  it.  In  both  cases, 
the  movements  are  consensual  only,  and  do  not  indicate  any  voluntary 
poAver ;  and  we  may  well  believe  that,  in  the  former  case  as  in  the 
latter,  though  felt  they  are  not  remembered;  an  active  state  of  the 
Cerebrum  being  essential  to  memory^  though  not  to  sensations,  which 
simply  excite  certain  actions. — When  the  Cerebral  Hemispheres  are 
being  removed,  slice  by  slice,  it  is  noticed  that  injuries  of  these  organs 
neither  occasion  any  signs  of  pain,  nor  give  rise  to  convulsive  move- 
ments. Even  the  Thalami  and  Corpora  Striata  may  be  wounded, 
without  the .  excitement  of  convulsions ;  whilst,  if  the  incisions  involve 
the  Tuber^ula  Quadrigemina,  convulsions  uniformly  occur.  It  has  been 
often  observed  in  Man,  that,  when  it  has  been  necessary  to  separate 
protruded  portions  of  the  brain  from  the  healthy  part,  no  sensation  was 
produced,  even  though  the  mind  was  perfectly  clear  at  the  time.  Hence 
it  would  appear  that  neither  is  the  Cerebrum  itself  the  centre  of  sensa- 
tion, nor  is  it  so  connected  with  that  centre,  as  to  be  able  to  convey  to 
it  sensory  impressions  of  an  ordinary  kind.  This  is  analogous  to  the 
condition  of  the  nerves  of  special  sense,  as  already  remarked.  That  no 
irritation  of  the  cerebral  substance  should  excite  convulsive  movements, 
is  a  very  remarkable  circumstance ;  and  it  seems  to  indicate,  that  the 
changes  which  mental  operations  produce  in  the  cerebral  fibres,  cannot 
be  imitated,  as  changes  in  other  motor  fibres  may  be,  by  physical  im- 
pressions. 

913.  As  already  stated,  the  relative  amount  of  Intelligence  in  diffe- 
rent animals  bears  so  close  a  correspondence  with  the  relative  size  and 
development  of  the  Cerebral  Hemispheres,  that  it  can  scarcely  be  ques- 
tioned that  these  constitute  the  organ  of  the  Reasoning  faculties,  and 


518  OF   THE  NERVOUS  SYSTEM  AND  ITS  ACTIONS. 

issue  the  mandates  by  which  the  Will  calls  the  muscles  into  action.  It 
must  be  borne  in  mind,  however,  that  size  is  not  by  any  means  the  only 
indication  of  their  comparative  development.  As  we  advance  from  the 
lower  to  the  higher  Vertebrata,  we  observe  a  marked  advance  in  the 
complexity  of  the  structure  of  the  Cerebrum.  Its  surface  becomes 
marked  by  convolutions,  that  greatly  increase  the  area  over  which 
blood-vessels  can  enter  it  from  the  surrounding  membranes  ;  and  in  pro- 
portion to  the  increase  in  the  number  and  depth  of  these,  do  we  find  an 
increase  in  the  thickness  of  the  layer  of  gray  matter,  which  is  the  source 
of  all  the  powers  of  the  organ.  The  arrangement  of  the  white  or  fibrous 
tissue,  which  forms  the  interior  of  the  mass,  also  increases  in  com- 
plexity ;  and  as  w^e  ascend  even  from  the  lower  Mammalia  up  to  Man, 
we  trace  a  marked  increase  in  the  number  of  the  fibres,  which  esta- 
blish communication  between  difi"erent  parts  of  the  organ.  It  is,  in  fact, 
not  merely  from  the  difi"erent  parts  of  the  gray  matter  which  forms  the 
surface  of  the  hemispheres,  that  these  commissural  fibres  arise ;  but  also 
from  those  isolated  portions  of  vesicular  substance,  which  are  found  in 
different  parts  of  their  interior ;  and  an  extremely  complex  system  is 
thus  formed,  which  is  still  but  very  imperfectly  understood. 

914.  The  most  important  group  of  commissural  fibres,  is  that  which 
connects  i\iQ  Sensory  with  the  Hemispheric  Ganglia;  that  is,  which 
radiates  from  the  Thalami  Optici  and  Corpora  Striata,  to  the  stratum  of 
gray  matter  which  forms  the  convoluted  surface  of  the  Cerebrum. 
These  fibres  constitute,  in  fact,  the  principal  part  of  the  white  sub- 
stance of  the  brain ;  the  remainder  being  made  up  by  the  commissures 
to  be  presently  described,  and  by  commissural  fibres  which  (it  is  pro- 
bable) connect  the  different  parts  of  the  Cerebral  surface  with  each 
other.  It  was  formerly  supposed  (and  is  still  maintained  by  many 
Anatomists),  that  the  radiating  fibres  which  may  be  traced  to  the  Cor- 
pora Striata  and  Thalami  Optici,  pass  through  these  bodies,  and  are 
continuous  with  the  Crura  Cerebri  and  consequently  with  the  sensory 
and  motor  tracts  of  the  Medulla  Oblongata.  But  when  the  small  size 
of  the  Crura  Cerebri  is  compared  with  the  relatively  enormous  bulk  of 
the  radiating  fibres,  it  is  obvious  that  the  former  can  only  contain  but 
a  very  small  proportion  of  the  latter;  and  as  no  absolute 'continuity 
has  been  traced,  it  appears  more  conformable  to  Anatomical  and  Phy- 
siological probability,  to  believe  that  the  fibres  of  the  Crura  Cerebri 
pass  no  further  upwards  than  the  Sensory  Ganglia,  and  that  the 
radiating  fibres  take  a  fresh  departure  from  these  bodies,  to  pass  to- 
wards the  surface  of  the  Cerebrum. — Thus,  then,  we  should  be  led  to 
regard  the  Spinal  Cord,  Medulla  Oblongata,  and  chain  of  Sensory 
Ganglia,  as  precisely  representing  the  entire  Nervous  System  of  Insects, 
the  character  of  whose  action  is  essentially  automatic;  and  to  consider 
the  Cerebrum  as  an  organ  superadded  to  its  summit,  receiving  all  its 
incitement  to  action  from  impressions  transmitted  to  it  through  the 
Sensory  Ganglia,  and  carrying  into  effect  its  volitional  determinations 
and  emotional  impulses,  not  (as  formerly  supposed)  by  immediately  ex- 
citing muscular  movements  through  nervous  communications  passing 
direct  from  the  convoluted  surface  of  the  Cerebrum,  but  by  playing 
downwards  upon  the  Automatic  apparatus  by  which  its  mandates  are 


COMMISSURES   OF   THE   CEREBRAL   HEMISPHERES. 


519 


carried  into  effect  (Figs.  155,  156).     Of  this  view  we  shall  presently 
find  that  there  is  strong  physiological  evidence. 

Fig.  156. 


Diagram  of  the  mutual  relations  of  the  principal  Encephalic  centres,  as  shown  in  a  vertical  section: — A, 
Cerebrum;  b,  Cerehellum ;  c,  Sensori-motor  tract,  including  the  Olfactive  ganglion  o7/,  the  Optic  opt,  and 
the  Auditory  aucl,  with  the  Thalami  Optici  thai,  and  the  Corpora  Striata  cs ;  D,  Medulla  Oblongata;  e,  Spinal 
Cord:— a,  olfactive  nerve;  &,  optic;  c,  auditory;  cf,  pneuraogastric;  e,  hypoglossal ;/,  spinal :  fibres  of  the 
medullary  substance  of  the  cerebrum  are  shown,  connecting  its  ganglionic  surface  with  the  sensori-motor 
tract. 

915.  The  two  Hemispheres  are  united  on  the  median  line  by  several 
transverse  commissures ;  of  which  the  Corpus  Callosum  is  the  most  im- 
portant. This  consists  of  a  mass  of  fibres  very  closely  interlaced  to- 
gether ;  which  may  be  traced  into  the  substance  of  the  hemispheres  on 
each  side,  particularly  at  their  lower  part,  where  they  are  connected 
with  the  thalami  optici  and  corpora  striata.  It  is  difficult,  if  not  impos- 
sible, to  trace  its  fibres  any  further ;  but  there  can  be  little  doubt  that 
they  radiate,  with  the  fibres  proceeding  from  the  bodies  just  named,  to 
the  different  parts  of  the  surface  of  the  hemispheres.  This  commissure 
is  altogether  absent  in  Fish,  Reptiles,  and  Bipds ;  and  it  is  partially  or 
completely  wanting  in  the  Mammalia  with  least  perfect  brain,  as  the 
Rodents  and  Marsupials. — The  other  transverse  commissures  rather 
belong  to  the  Sensory  Ganglia  than  to  the  Cerebral  hemispheres.  Thus 
the  anterior  commissure  particularly  unites  the  Corpora  Striata  of  the 
two  sides ;  but  many  of  its  fibres  pass  through  those  organs,  and  radiate 
towards  the  convolutions  of  the  hemispheres,  especially  those  of  the 
middle  lobe.  This  commissure  is  particularly  large  in  those  Marsu- 
pials, in  which  the  corpus  callosum  is  deficient. — The  posterior  com- 
missure is  a  band  of  fibres  which  connects  the  Optic  Thalami ;  crossing 
over  from  the  posterior  extremity  of  one  to  that  of  the  other. — Besides 
these,  there  are  other  groups  of  fibres,  which  seem  to  have  similar  com- 
missural functions,  but  which  are  intermingled  with  vesicular  substance. 


520  OF  THE  NERVOUS   SYSTEM   AND  ITS  ACTIONS. 

Such  are  the  soft  commissure,  which  also  extends  between  the  Thalami ; 
the  Pons  Tarini,  which  extends  between  the  two  crura  or  peduncles  of 
the  Cerebrum;  and  the  Tuber  Cinereum,  which  seems  to  unite  the 
optic  tracts  with  the  thalami,  the  corpus  callosum,  the  fornix,  &c.,  and 
to  be  a  common  point  of  meeting  for  several  distinct  groups  of  fibres. 

916.  The  anterior  and  posterior  parts  of  the  hemispheres,  moreover, 
are  connected  by  longitudinal  Commissures,  of  w^hich  some  lie  above, 
and  some  below,  the  corpus  callosum ;  and  of  these,  also,  a  part  belong 
to  the  Sensory  Ganglia.  Above  the  transverse  fibres  of  the  corpus 
callosum,  there  is  a  longitudinal  tract  on  each  side  of  the  median  line, 
which  serves  to  connect  the  convolutions  of  the  anterior  and  posterior 
lobes  of  the  brain. — And  above  this,  again,  is  the  superior  longitudinal 
commissure,  which  is  formed  by  the  fibrous  matter  of  the  great  convolu- 
tion nearest  the  median  plane  on  the  upper  surface  of  the  brain,  and 
which  connects  the  convolutions  of  the  anterior  and  middle  lobe  with 
those  of  the  posterior. — Beneath  the  great  transverse  commissure,  we 
find  the  most  extensive  of  all  the  longitudinal  commissures,  namely,  the 
Fornix.  This  is  connected  in  front  with  the  optic  thalami,  the  mammil- 
lary  bodies,  the  tuber  cinereum,  &c. ;  and  behind,  it  spreads  its  fibres 
over  the  hippocampi  (major  and  minor),  which  are  njothing  else  than 
peculiar  convolutions  that  project  into  the  posterior  and  descending 
cornua  of  the  lateral  ventricles.  The  fourth  longitudinal  commissure  is 
the  toenia  semicircularis,  which  forms  part  of  the  same  system  of  fibres 
with  the  fornix  ;  connecting  the  corpus  mammilare  and  thalamus  opticus 
with  the  middle  lobe  of  the  cerebral  hemisphere.  If,  as  Dr.  Todd  has 
remarked,  we  could  take  away  the  corpus  callosum,  the  gray  matter  of 
the  internal  convolution,  and  the  ventricular  prominence  of  the  optic 
thalami,  then  all  these  commissures  would  fall  together,  and  become 
united  as  one  and  the  same  series  of  longitudinal  fibres. — It  is  curious 
that  there  should  be  no  direct  communication  between  the  Cerebral 
hemispheres  and  the  Cerebellum ;  the  only  commissural  band  between 
them  being  the  processus  a  cerehello  ad  testes,  which  passes  onwards, 
through  the  Tubercula  Quadrigemina,  to  the  Thalamus  Opticus  on  each 
side.  This  would  seem  to  confirm  the  idea  of  the  complete  distinctness 
of  their  functions. 

917.  The  Cerebrum  appears  to  be  the  instrument  of  all  those  psychi- 
cal operations,  which  are  superadded,  in  Man  and  the  higher  Verte- 
brata,  to  mere  sensations.  The  impressions  which  are  merely  felt  in 
the  sensorium,  give  rise,  when  they  pass  upwards  into  the  Cerebrum, 
to  Ideas,  which  then  become  the  material  (so  to  speak)  of  all  the  higher 
mental  processes.  These  processes  may  be  ranked  under  two  dis- 
tinct heads,  namely,  the  Emotional  and  the  Intelligential ;  the  former 
being  most  intimately  connected  with  the  sensations  which  prompt  them, 
whilst  the  latter  are  commonly  of  a  much  more  abstract  character. 
The  Emotions  may,  in  fact,  be  considered  as  feelings  of  pleasure  or  pain 
associated  with  particular  classes  of  ideas ;  and  it  is  this  association 
which  gives  them  the  character  of  the  moving  or  active  powers  of  the 
mind,  and  which  makes  them,  either  directly  or  indirectly,  the  springs 
of  the  greater  part  of  our  actions.  When  strongly  excited,  the  Emo- 
tions may  produce  movements  which  the  Will  may  not  be  able  to  re- 


FUNCTIONS   OF  THE   CEREBRUM.  521 

strain  ;  as  when  we  burst  into  laughter  at  some  ludicrous  image  presented 
to  the  mind,  either  by  a  present  sensation  or  by  an  act  of  the  Memory 
or  Imagination,  notwithstanding  the  strongest  inducements  presented  by 
"time,  place,  and  circumstance"  to  a  preservation  of  our  gravity. 
The  distinctness  of  the  character  of  Emotional  and  Volitional  move- 
ments is  further  evident  from  this,  that  cases  of  paralysis  not  unfre- 
quently  occur  (especially  in  the  facial  nerve,  through  which  most  of  the 
muscles  of  "expression"  are  excited  to  action),  in  which  the  muscles  are 
obedient  to  one  class  of  impulses,  while  the  other  exerts  no  power  over 
them.  Thus,  in  one  instance,  the  muscles  of  one  side  of  the  face  were 
palsied  in  such  a  manner,  that  the  patient  could  not  voluntarily  close 
his  eye,  nor  draw  his  mouth  to^^ards  that  side ;  yet  when  any  ludicrous 
circumstance  caused  him  to  laugh,  their  usual  play  was  manifested  in 
the  expression  of  his  countenance.  And  in  another  case,  the  muscles 
were  obedient  to  the  will;  but  when  the  individual  laughed  or  cried 
under  the  influence  of  an  emotion,  it  was  only  on  one  side  of  his  face. 
To  these  may  be  added  another  case,  in  which  the  right  arm  was  com- 
pletely palsied,  so  that  the  individual  had  not  the  least  voluntary  power 
over  it ;  yet  it  was  violently  agitated,  whenever  he  met  a  friend  whom  he 
desired  to  greet. — The  influence  of  an  undue  tendency  to  Emotional 
excitement,  is  remarkably  seen  in  what  are  ordinarily  termed  Hysterical 
states  of  the  system ;  in  which  violent  convulsive  paroxysms  are  fre- 
quently brought  on  by  the  most  trivial  causes,  if  these  should  call  the 
passions  or  affections  of  the  mind  into  undue  activity.  There  can  be  no 
doubt  that  many  of  the  peculiar  actions  performed  by  the  subject  of 
what  is  termed  Mesmeric  influence,  are  the  result  of  a  condition  of  this 
nature.  There  appears  to  be,  in  such  persons,  a  proneness  to  activity 
of  the  consensual  and  emotional  parts  of  the  nervous  centres,  which 
manifests  itself  most  strongly  when  the  control  of  the  wall  is  withdrawn ; 
and  thus  very  slight  impressions  produce  very  powerful  involuntary 
movements, — especially  when  this  response  is  favoured  by  the  strong 
desire,  on  the  part  of  the  patient,  to  exhibit  any  particular  manifestation 
that  is  known  to  be  expected  by  the  bystanders. 

918.  It  has  been  supposed  by  some,  that  the  Emotional  movements 
of  Man  and  the  higher  animals  may  be  ranked  in  the  same  category 
with  the  Instinctive  actions  of  the  lower ;  and  that  the  Desires  of  the 
former  are  comparable  to  the  instinctive  Propensities  of  the  latter. 
But  this  comparison  is  erroneous  ;  for  what  we  t^rm  propensities  (among 
the  lower  animals)  are  nothing  else  than  tendencies  to  perform  particular 
movements  in  respondence  to  particular  sensations,  without  any  idea  of 
the  purpose  of  the  movement  or  of  the  object  which  has  excited  it ;  whilst  an 
Emotion  involves  an  idea  of  the  object  which  has  called  it  up,  and  a  Desire 
involves  a  conception  of  the  object  to  be  attained. — The  imitative  actions 
afford  a  good  example  of  the  difference  between  a  propensity  and  a 
desire.  The  former  is  manifested  in  such  imitative  movements  as  are 
purely  consensual ;  the  sensation,  which  is  the  mainspring  of  the  action 
in  each  case,  exciting  a  respondent  automatic  movement,  as  when  we 
yawn  involuntarily  from  seeing  or  hearing  the  action  performed  by 
another,  or  as  when  children  learn  undesignedly  to  perform  many  of 
the  movements  which  they  witness  in  adults.     This  propensity  to  in- 


522  OP  THE  NERVOUS   SYSTEM   AND   ITS  ACTIONS. 

voluntary  imitation  is  much  stronger  in  some  individuals  than  in  others. 
On  the  other  hand,  imitative  actions  may  be  voluntarily  performed,  as 
the  result  of  a  desire  to  execute  them,  which  involves  a  distinct  idea  of 
the  object ;  and  the  moving  force  of  this  desire  is  derived  from  the 
pleasure  which  the  individual  derives  from  the  performance,  and  which 
he  finds  either  in  the  act  itself,  or  in  the  enjoyment  which  it  affords  to 
others,  or  in  its  prospective  benefits  (pecuniary  or  otherwise)  to  himself. 
Thus  we  see  that  the  Mind  (properly  so  called)  is  concerned  in  all  Emo- 
tional actions ;  whilst  there  is  no  evidence  of  the  participation  of  any  higher 
attribute  than  sensation  in  the  purely  Instinctive  acts ;  and  even  this  is 
not  a  requisite  link  in  the  chain,  by  which  many  of  the  movements  are 
excited,  that  are  usually  grouped  together  under  that  designation. 

919.  Again,  the  Emotions  may  be  excited  by  operations  of  the  Mind 
itself,  as  well  as  by  sensations  immediately  received  from  without. 
Thus,  involuntary  laughter  may  result  from  a  ludicrous  idea,  called  up 
by  some  train  of  association,  and  having  no  obvious  connexion  with  the 
sensation  which  first  set  this  process  in  operation ;  and  the  various  move- 
ments of  the  face  and  person  by  which  Actors  endeavour  to  express  strong 
emotions,  are  most  effectual  in  conveying  their  meaning,  when  they  result 
^from  the  actual  working  of  the  emotions  in  the  mind  of  the  performer, 
/  "who  has,  by  an  effort  of  the  will,  identified  himself  (so  to  speak)  with 
'  the  character  he  personates.  A  still  more  remarkable  case  is  that  in 
which  paroxysms  of  Hysterical  convulsion,  in  themselves  beyond  the 
power  of  the  Will  to  excite  or  to  control,  are  brought  on  by  a  voluntary 
effort ;  this  being  exerted,  not  in  the  attempts  to  perform  the  move- 
ments, but  in  "  getting  up,"  so  to  speak,  the  state  of  feeling,  from 
which,  when  it  is  once  excited,  the  movements  spontaneously  flow.  In 
all  these  instances,  and  others  of  like  nature,  it  would  seem  as  if  the 
agency  of  the  Cerebrum  produced  the  same  condition  in  the  Automatic 
centres,  as  that  which  is  more  directly  excited  by  sensations  received 
through  their  own  afferent  nerves. — But  on  the  other  hand,  the  Emo- 
tions, by  their  influence  on  the  Reasoning  processes,  are  largely  con- 
cerned in  many  actions  which  are  strictly  voluntary  ;  in  fact  it  may  be 
questioned  whether  there  are  any  of  our  actions,  the  power  necessary  for 
whose  performance  is  not  derived,  directly  or  indirectly,  from  emotional 
states  of  mind ;  all  our  motives  to  any  kind  of  exertion  being  found,  if  care- 
fully analyzed,  to  have  reference  to  pleasure  to  be  derived,  or  pain  to  be 
avoided,  either  in  the  very  performance  of  the  action,  or  in  the  conse- 
quences which  our  reasoning  processes  connect  with  it.  And  it  will  be 
found  that  the  difference  between  those  persons  who  are  said  to  act  from 
feeling^  and  those  who  are  said  to  be  guided  by  reason,  is  not  precisely 
what  these  terms  imply ;  for  the  actions  of  both  are  equally  determined 
by  the  motives  supplied  by  emotional  states ;  and  the  difference  rather 
lies  in  this,  that  one  class  act  on  their  first  impulses  without  considering 
the  consequences,  whilst  the  other  calculate  the  remoter  results,  and 
weigh  the  future  pain  against  the  present  pleasure  the  ultimate  enjoy- 
ment against  the  immediate  distress. — The  Emotional  states  are  pecu- 
liarly liable  to  be  influenced  by  the  condition  of  the  corporeal  system ; 
thus  a  very  slight  depravation  of  the  blood  may  produce  an  irresistible 
tendency  to  take  a  gloomy  view  of  everything  to  which  the  mind  may 

J 


FUNCTIONS   OF   THE   CEREBRUM.  523 

be  directed,  and  especially  of  all  that  relates  to  the  individual ;  whilst 
that  condition  of  perfect  health  which  is  derived  from  wholesome  recrea- 
tion, fresh  air,  active  exercise,  &c.,  is  almost  always  accompanied  with  a 
degree  of  cheerfulness  and  elasticity,  which  occasions  even  real  evils  to 
be  but  comparatively  little  felt. 

920.  When  we  turn  our  attention  to  the  Intelligential  actions  of 
which  the  Cerebrum  appears  (in  our  present  state  of  being)  to  be  the 
exclusive  instrument,  we  perceive  that  the  attribute  by  which  they  are 
distinguished  both  from  the  Instinctive  and  Emotional,  is  their  inten- 
tional or  pu7'posive  performance,  in  accordance  with  the  mental  concep- 
tion of  the  object  to  be  attained,  and  the  intellectual  belief  as  to  the 
most  advantageous  means  of  accomplishing  it.  The  decision  thus 
formed  by  the  Reasoning  processes,  is  put  into  operation  by  the  Will ; 
and  thus  it  is  the  characteristic  of  a  Voluntary  act,  that  it  is  designed 
by  the  individual  to  answer  a  certain  purpose  which  is  distinctly 
present  to  the  mind. — Now  when  we  come  to  analyze  the  faculties 
concerned  in  this  class  of  operations,  we  find  that  the  one  most  closely 
related  to  the  simple  Sensorial  powers  already  treated  of,  and  at  the 
same  time  most  essential  to  all  the  higher  operations,  is  Memory, 
This  faculty  is  one  of  those  first  awakened  in  the  opening  mind  of  the 
Infant;  and  we  find  traces  of  it  in  animals  that  seem  to  be  otherwise 
guided  by  pure  Instinct.  It  obviously  affords  the  first  steps  towards 
the  exercise  of  the  reasoning  powers ;  since  no  experience  can  be  gained 
without  it,  and  the  foundation  of  all  intelligent  adaptation  of  means  to 
ends  lies  in  the  application  of  the  knowledge  which  has  been  acquired 
and  stored  up  in  th€  mind.  There  is  strong  reason  to  believe  that  this 
attribute  belongs  to  the  Cerebrum  exclusively;  no  impressions  made 
upon  the  Sensorial  centres  being  ever  remembered,  unless  they  are 
registered  (as  it  were)  in  this  organ.  And  further,  there  is  evidence 
that  no  impression  of  this  kind  once  made  upon  the  Cerebrum  is  ever 
entirely  lost,  in  the  normal  state ;  although  disease  or  accident  will 
sometimes  occasion  a  complete  destruction  of  the  memory,  or  will 
obliterate  the  remembrance  of  a  particular  class  of  objects  or  of  ideas. 
All  memory,  however,  seems  to  depend  upon  the  principle  of  Sugges- 
tion ;  one  idea  being  linked  with  another,  or  with  a  particular  sensa- 
tion, in  such  a  manner  as  to  be  called  up  by  its  recurrence  ;  and  a 
period  of  many  years  frequently  intervening,  without  tbat  combination 
of  circumstances  presenting  itself  which  is  Requisite  to  arouse  the 
dormant  impression  of  some  early  event.  Sometimes  this  combination 
occurs  in  Dreaming,  Delirium,  or  Insanity,  three  states  which  agree  in 
this,  that  the  Will  has  no  control  over  the  current  of  thought;  and 
ideas  are  thus  recalled,  of  which  the  mind  in  a  state  of  healthy  activity 
has  no  remembrance. 

921.  It  is  upon  the  ideas  aroused  in  the  mind  by  Sensorial  changes, 
or  recalled  by  Conception^  or  evolved  by  the  process  of  Reflection  (in 
which  the  mind  perceives  its  own  operations,  and  traces  relations 
amongst  its  objects  of  thought),  or  generated  by  the  Imagination 
(which  really  acts,  however,  rather  by  combining  into  new  forms,  than 
by  creating  altogether  de  novo),  that  all  acts  of  Reasoning  are  based. 
These  consist,  for  the  most  part,  in  the  aggregation  and  collocation  of 


524  OF   THE   NERVOUS   SYSTEM  AND   ITS  ACTIONS. 

ideas,  the  decomposition  of  complex  ideas  into  more  simple  ones,  and 
the  combination  of  simple  ideas  into  general  expressions ;  in  which  are 
exercised  the  faculty  of  Comparison^  by  which  the  relations  and  con- 
nexions of  ideas  are  perceived,  that  of  Abstraction^  by  which  we  fix 
our  attention  on  any  particular  qualities  of  the  object  of  our  thought, 
and  isolate  it  from  the  rest,  and  that  of  G-eneralization,  by  which  we 
grasp  in  our  minds  some  definite  notions  in  regard  to  the  general 
relations  of  those  objects.  These  are  the  processes  chiefly  concerned 
in  the  simple  acquirement  of  Knowledge,  with  which  class  of  opera- 
tions the  Emotional  part  of  our  nature  has  very  little  participation, 
save  as  furnishing  the  desire  which  may  be  the  necessary  incitement 
to  the  exertion  of  the  intellect.  A  certain  measure  of  intellectual 
activity  seems  natural  to  Man,  provided  that  the  development  of  the 
mind  has  taken  place  under  favourable  circumstances  ;  and  our  highest 
pleasures  are  connected  with  the  healthful  and  almost  spontaneous 
exercise  of  its  faculties. 

922.  But  the  Will  possesses  a  determining  power  over  the  mental 
as  well  as  over  the  bodily  operations ;  and  it  is,  in  fact,  this  determi- 
ning power,  which  is  the  source  of  the  self-control  that  characterizes  the 
well-regulated  mind  of  Man,  and  distinguishes  him  alike  from  the 
madman  and  the  brute.  The  regulation  of  our  conduct  consists  in  the 
application  of  our  reasoning  powers  to  the  circumstances  of  our  con- 
dition, and  in  the  due  regulation  of  those  emotional  tendencies,  which 
(as  already  pointed  out,  §  919)  are  the  moving  springs  of  our  actions. 
However  powerful  these  tendencies  may  be,  there  can  be  no  doubt, 
that  we  possess  within  ourselves  the  means  of  checking  them,  by 
withdrawing  our  minds  by  a  voluntary  effort  from  the  thoughts  which 
they  suggest,  as  well  as  by  calling  forth  opposing  influences  within  us, 
so  that  the  decision  which  is  finally  arrived  at  is  something  very 
different  from  that  which  the  first  "  balance  of  motives"  would  have 
produced.  It  is  the  deficiency  or  entire  loss  of  this  power  of  self- 
control,  that  usually  constitutes  the  first  step  in  the  development  of 
Insanity ;  for  this  state  generally  consists,  not  so  much  in  a  perversion 
of  the  reasoning  processes,  as  in  a  disorder  of  the  emotional  state, 
which  causes  the  patient  to  dwell  upon  particular  trains  of  thought, 
until  his  feelings  in  relation  to  them  become  exaggerated  or  perverted ; 
and  at  last  intellectual  delusions  arise,  from  the  habit  of  viewing  every- 
thing that  comes  before  the  mind  through  a  distorted  medium,  and 
from  the  substitution  of  the  patient's  morbid  imaginings  for  real  occur- 
rences. ^  In  what  is  now  termed  impulsive  Insanity,  there  is  intellectual 
perversion ;  but  a  desire  of  some  kind  is  so  powerfully  excited,  that 
the  Will  cannot  control  it.  And  every  phase  may  be  witnessed 
between  a  state  of  this  kind,  which  renders  the  individual  an  irrespon- 
sible agent,  and  that  mental  condition  in  which  the  individual,  though 
originally  fully  able  to  control  himself,  habitually  gives  way  to  his 
passions,  and  thus,  by  their  continual  indulgence,  at  last  allows  them 
to  become  the  dominant  powers  of  his  mind. 

923.  Although  the  Will  has  been  usually  regarded  as  directly  deter- 
mining those  muscular  movements  which  are  usually  distinguished  as 
Voluntary,  through  the  intermediation  of  fibres  originating  in  the  cere- 


FUNCTIONS   OF   THE    CEREBRUM.  525 

bral  convolutions  and  proceeding  to  the  muscles,  yet  a  careful  analysis 
of  the  process  fully  bears  out  the  idea  already  put  forwards,  that  the 
Will  really  operates  through  the  Automatic  apparatus,  exciting  parti- 
cular groups  of  muscular  actions,  just  as  they  would  be  called  forth  by 
sensations  directly  excited  by  external  objects.  For  it  has  been  shown 
that  the  Craniospinal  Axis  (consisting  of  the  Sensory  Ganglia,  Me- 
dulla Oblongata,  and  Spinal  Cord)  receives  all  the  sensory  nerves, 
and  gives  origin  to  all  the  motor  ;  and  that  the  fibres  which  pass  between 
the  Cerebral  convolutions  and  the  Sensory  Ganglia,  probably  serve  to 
bring  these  centres  into  mutual  relation,  and  are  not  continuous  with 
those  of  any  nerves,  either  sensory  or  motor.  And  we  might  expect, 
therefore,  that  the  addition  of  a  Cerebrum  to  this  automatic  apparatus 
would  have  the  effect  of  supplying  a  new  stimulus  to  movement,  which, 
whilst  proceeding  from  mental  operations,  should  still  act  through  the 
same  mechanism  as  that  already  provided  for  the  reflex  and  consensual 
movements.  Now  when  we  attentively  consider  the  nature  of  what  we 
are  accustomed  to  call  voluntary  action,  we  perceive  that  the  agency  of 
the  Will  is  limited  to  the  determination  of  the  result ;  and  that  it  has 
nothing  to  do  with  the  selection  and  co-ordination  of  the  individual 
movements,  by  which  that  result  is  brought  about.  If  it  were  other- 
wise, we  should  be  dependent  upon  our  anatomical  knowledge,  for  our 
power  of  performing  even  the  simplest  movements  of  the  body.  Again, 
there  are  very  few  cases  in  which  we  can  single  out  any  individual 
muscle,  and  put  it  into  action  independently  of  others  ;  and  the  cases  in 
which  we  can  do  so,  are  those  in  which  a  single  muscle  is  concerned  in 
producing  the  result,  as  in  the  elevation  of  the  eyelid ;  and  we  then 
really  single  out  the  muscle  by  "willing"  the  result.  Thus,  then,  how- 
ever startling  the  position  may  at  first  appear,  we  have  a  right  to  afiirm 
that  the  W^ill  cannot  exert  any  direct  or  immediate  power  over  the 
muscles  ;  but  that  its  determinations  are  carried  into  effect  through  an 
intermediate  mechanism,  which,  without  any  further  guidance  on  our  own 
part,  selects  and  combines  the  particular  muscles  whose  contractions  are 
requisite  to  produce  the  desired  movement.  We  have  seen  that  the 
Sensorial  centres  play  (so  to  speak)  upon  the  Cerebrum,  sending  to  it 
impressions  of  a  kind  fitted  to  call  forth  its  peculiar  activity  as  an  instru- 
ment of  purely  mental  operations ;  and  in  return,  the  Cerebrum  appears 
to  play  downwards  upon  the  motor  portion  of  the  automatic  apparatus, 
sending  to  it  volitional  impulses  which  excite  its  motorial  activity.  And 
thus  we  see  that  the  very  same  action  may  be  excited  through  an  impres- 
sion conveyed  to  the  centres  of  the  whole  system  through  some  one  or 
more  nerves  of  the  external  senses,  or  through  the  fibres  converging  to 
them  from  the  cerebral  convolutions,  which  have  been  not  unaptly 
called  "  the  nerves  of  the  internal  senses  ;''  and  may  hence  be  automatic 
in  the  first  case,  and  voluntary  in  the  second.  For  example,  in  the  act 
of  Coughing,  we  have  the  very  same  combination  and  succession  of 
diverse  but  mutually-related  actions,  whether  the  operation  be  excited 
by  the  presence  of  an  irritating  particle  in  the  air-passages,  or  be  per- 
formed as  the  consequence  of  a  voluntary  effort.  And  a  little  attention 
to  his  own  consciousness  will  satisfy  the  reader,  that  as  regards  the 
selection  and  co-ordination  of  the  movements  which  are  concerned,  the 


526  OF  THE  NERVOUS   SYSTEM   AND   ITS   ACTIONS. 

Intelligence  and  Will  are  no  more  concerned  in  the  one  case  than  in  the 
other. — And  hence  it  follows,  that  all  the  movements  which  are  per- 
formed by  the  instrumentality  of  the  Cerebro-spinal  system  of  ganglia 
and  nerves,  are  in  their  essential  nature  automatic ;  and  that  their  cha- 
racter as  Reflex,  Instinctive,  Emotional,  or  Voluntary,  is  entirely 
dependent  on  the  nature  and  seat  of  the  impulses  which  respectively 
originate  them. 

924.  There  are  various  conditions,  some  of  them  natural,  others 
morbid,  in  which  the  distinctness  of  the  functions  of  the  Cerebral  Hemi- 
epheres  is  well  marked.  Thus  in  profound  Sleep,  they  seem  to  be 
entirely  dormant ;  the  Spinal  Cord  and  Medulla  Oblongata,  by  which 
the  necessary  reflex  actions  are  carried  on,  being  alone  in  a  state  of 
activity.  In  this  condition,  the  Sensory  ganglia  also  appear  to  be  in  a 
torpid  state ;  but  in  less  profound  sleep,  actions  are  often  performed, 
which  may  be  referred  to  the  consensual  group, — being  such  as  the  sen- 
sation would  immediately  prompt,  without  any  reflection,  and  not  being 
remembered  in  the  waking  state.  Thus  we  turn  in  our  beds,  under  the 
influence  of  an  uneasy  sensation ;  or  we  give  some  sign  of  recognition 
when  our  names  are  called.  The  first  of  these  appears  to  be  a  purely 
consensual  movement,  being  as  automatic  as  if  it  were  a  reflex  action ; 
the  other  seems  to  have  become  as  automatic,  by  the  influence  of  habit, 
and  to  belong  to  that  class  of  secondarily  automatic  actions,  in  which 
the  movement,  though  at  first  directed  by  the  will,  has  become,  after 
very  frequent  performance,  so  closely  associated  with  the  guiding  sug- 
gestion, as  to  be  called  forth  by  it  alone  (§  904). — In  the  Coma  of  Apo- 
plexy, Narcotic  Poisoning,  &c.,  we  witness  the  same  gradations  as  in 
ordinary  sleep.  When  it  is  least  profound,  it  seems  to  affect  the  Cere- 
bral hemispheres  alone  ;  the  Sensory  Ganglia  being  still,  in  some  degree, 
open  to  the  reception  of  impressions.  When  complete,  however,  none 
but  reflex  actions  can  be  excited  ;  and  if  it  advance  to  a  fatal  termina- 
tion, it  does  so  by  the  supervention  of  the  same  state  of  torpidity  in  the 
Medulla  Oblongata,  whereby  the  respiratory  movements  are  brought  to 
a  close.  These  movements  do  not  cease  until  the  power  of  deglutition 
has  been  lost,  and  until  the  eye  ceases  to  close,  when  the  edge  of  the 
lid  is  irritated ;  but  when  this  is  the  case,  a  fatal  termination  may  be 
apprehended,  as  it  is  thus  shown  that  the  torpor  is  extending  to  the 
Spinal  system  of  nerves. — In  the  condition  of  Dreaming,  it  would  seem 
as  if  the  Cerebrum  were  'partially  active  ;  a  train  of  thought  being  sug- 
gested, frequently  by  sensations  from  without ;  which  is  carried  on  with- 
out any  controlling  or  directing  power  on  the  part  of  the  Mind  ;  and 
which  is  not  corrected,  or  is  only  modified  in  a  limited  degree,  by  the 
knowledge  acquired  by  experience.  This  condition  is  still  more  remark- 
able in  Somnambulism,  or  (as  it  has  been  better  termed)  Sleep-waking ; 
in  which  the  dreams  are  not  only  acted^  but  may  be  often  acted  on  with 
the  utmost  facility, — a  suggestion  conveyed  through  any  of  the  senses 
excepting  sight  (which  is  usually  in  abeyance)  being  apprehended  and 
followed-up  with  the  utmost  readiness,  and,  in  like  manner,  with  little 
or  no  correction  from  experience.  Between  this  condition,  and  that  of 
ordinary  dreaming,  on  the  one  hand,  and  that  of  complete  insensibility 
on  the  other,  there   is  every   shade  of  variety;  which   is   presented 


FUNCTIONS   OF   THE   SYMPATHETIC   SYSTEM.  527 

by  different  individuals,  or  by  the  same  individual  at  different  times. 
The  Cerebellum,  in  the  Sleep-waking  state,  seems  to  be  frequently  in  a 
condition  of  peculiar  activity;  a  remarkable  power  of  balancing  and 
combining  the  movements  of  the  body,  being  often  exhibited. 

925.  On  the  other  hand,  there  may  be  an  undue  exaltation  or  a  per= 
version  of  mental  activity,  without  any  affection  of  the  sensorial  appa- 
ratus. This  is  well  seen,  for  example,  in  the  first  stage  of  Alcoholic 
excitement,  and  in  that  of  Mania,  Phrenitis,  and  other  disorders  in 
which  the  Cerebral  Hemispheres  are  especially  affected.  Frequently, 
as  in  the  case  of  Alcohol,  Opium,  Haschish,  &c.,  we  may  directly  attri- 
bute the  morbid  action  of  the  Cerebrum  to  the  presence  of  a  poison  in 
the  blood  which  permeates  it ;  and  there  is  strong  reason  to  believe  that 
many  other  forms  of  delirium  are  partly  due  to  a  perverted  state  of  that 
fluid.  On  the  other  hand,  there  can  be  no  doubt  that  an  extreme 
depression  of  intellectual  power,  as  well  as  of  the  emotional  state,  is 
often  to  be  attributed  to  a  depravation  of  the  blood ;  a  slight  accumula- 
tion of  bile  being  very  prone  to  occasion  this  state  in  some  individuals, 
and  an  entire  change  being  effected  by  a  mild  dose  of  mercurial  prepa- 
rations, which,  by  eliminating  the  bile,  restores  the  circulating  fluid  to 
its  proper  purity.  And  it  may  be  fairly  suspected,  that  the  foul  atmo- 
sphere in  the  midst  of  which  a  large  class  of  our  population  habitually 
lives,  has  the  effect,  by  keeping  their  blood  charged  with  noxious  mat- 
ters, of  so  perverting  the  actions  of  the  brain,  that  neither  the  intellec- 
tual powers  nor  the  moral  sense  can  be  duly  exercised ;  and  thus  it  may 
be  anticipated  that  Sanitary  Reform  will  largely  benefit- not  merely  the 
corporeal  but  the  mental  and  moral  health  of  those,  whose  position  is  at 
present  one  of  fearful  degradation  from  the  want  of  it. 

8.  Functions  of  the  Sympathetic  System. 

926.  The  Cerebro-Spinal  apparatus,  of  which  the  several  parts  have 
now  been  described,  is  not  the  only  system  of  ganglia  and  nerve-trunks, 
that  is  contained  within  the  body  of  a  Vertebrated  animal.  There  is 
another  system,  having  its  own  set  of  centres,  and  its  own  distribution 
of  branches,  characterized  also  by  a  peculiarity  in  the  nature  of  the 
nervous  fibres  of  which  its  trunks  are  composed,  and  communicating  at 
numerous  points  with  the  preceding.  It  will  be  remembered  that,  in 
front  of  the  vertebral  column,  there  is  a  series  of  ganglia  on  each  side ; 
communicating,  on  the  one  hand,  with  the  spind!l  nerves,  as  they  issue 
from  the  vertebral  canal ;  and  also  connecting  themselves  with  the  two 
large  Semilunar  ganglia,  which  lie  amidst  the  abdominal  viscera  ;  as  well 
as  with  a  series  of  ganglia,  that  is  found  near  the  base  of  the  heart.  In 
the  head,  also,  there  are  numerous  scattered  ganglia,  which  evidently 
belong  to  the  same  system ;  having  several  communications  with  the 
cephalic  nerves ;  and  being  also  connected  with  the  chain  of  ganglia  in 
the  neck.  The  branches  proceeding  from  this  series  of  ganglia  are  dis- 
tributed, not  to  the  skin  and  muscles  (like  those  of  the  cerebro-spinal 
system),  but  to  the  organs  of  digestion  and  secretion,  to  the  heart  and 
lungs,  and  particularly  to  the  walls  of  the  blood-vessels,  on  which  they 
form  a  plexus  whose  branches  probably  accompany  their  minutest  rami- 


528  OF   THE   NERVOUS    SYSTEM   AND   ITS   ACTIONS. 

fications.  The  peculiar  connexion  of  this  system  of  nerves  with  the 
organs  of  vegetative  life,  has  caused  it  to  receive  the  designation  of  the 
Nervous  System  of  Organic  Life;  the  Cerebro-Spinal  system  being 
termed  the  Nervous  System  of  Animal  Life.  It  is  also  not  unfrequently 
termed  the  ganglionic  system ;  on  account  of  the  separation  of  its  centres 
into  scattered  ganglia,  which  forms  a  striking  contrast  to  the  concentra- 
tion that  is  so  evident  in  the  Cerebro-spinal  system.  But  this  term  is 
objectionable,  as  leading  to  a  supposed  analogy  between  this  system  and 
the  general  nervous  system  of  Invertebrata,  whose  centres  are  equally 
scattered ; — an  analogy  which  is  completely  erroneous,  since,  as  we  have 
seen,  this  last  is  chiefly  the  representative  of  the  Cerebro-Spinal  system 
of  Vertebrated  animals.  The  term  Sympathetic  is  perhaps  the  best ; 
although  it  must  not  be  supposed  that  this  system  of  nerves  is  the 
instrument  of  by  any  means  all  the  sympathies,  which  manifest  them- 
selves between  different  organs. 

927.  The  Sympathetic  system  contains  both  classes  of  nervous  fibres  ; 
— the  ordinary  white  tubular  fibres,  all  of  which  are  probably  derived 
from  the  Cerebro-Spinal  system ;  and  the  gra^  or  gelatinous  fibres,  part 
of  which  seem  to  belong  to  itself  (§  375).  Thus  we  may  consider  each 
system  as  intermingling  itself  with  the  other ; — the  Cerebro-Spinal  sys- 
tem transmitting  some  of  its  fibres,  both  motor  and  sensory,  into  the 
Sympathetic ; — whilst  the  Sympathetic  is  represented  in  the  Cerebro- 
spinal system,  by  certain  fibres  and  collections  of  vesicular  matter  of 
its  own.  The  trunks  that  proceed  from  the  Semilunar  ganglia,  are 
almost  entirely  composed  of  gray  or  organic  fibres  ;  whence  it  is  evident 
that  these  ganglia  are  to  be  regarded  as  the  true  centres  of  the  Sympa- 
thetic system.  On  the  other  hand,  the  trunks  which  issue  from  the 
chain  of  spinal  ganglia,  contain  a  large  admixture  of  white  or  tubular 
fibres. 

928.  The  Sympathetic  nerves  possess  a  certain  degree  of  power  of 
exciting  Muscular  contractions,  in  the  various  parts  to  which  they  are 
distributed.  Thus  by  irritating  them,  immediately  after  the  death  of 
an  animal,  contractions  may  be  excited  in  any  part  of  the  alimentary 
canal,  from  the  pharynx  to  the  rectum,  according  to  the  trunks  which 
are  irritated, — in  the  heart,  after  its  ordinary  movements  have  ceased, 
— in  the  aorta,  vena  cava,  and  thoracic  duct, — in  the  ductus  choledochus, 
uterus,  fallopian  tubes,  vas  deferens,  and  vesiculse  seminales.  But  the 
very  same  contractions  may  be  excited,  by  irritating  the  roots  of  those 
Spinal  nerves,  from  which  the  Sympathetic  trunks  receive  their  white 
fibres;  and  there  is,  consequently,  strong  reason  to  believe  that  the 
motor  power  of  the  latter  is  entirely  dependent  upon  the  Cerebro-spinal 
system.  Whatever  sensory  endowments  the  Sympathetic  trunks  pos- 
sess, are  probably  to  be  referred  to  the  same  connexion.  In  the  ordi- 
nary condition  of  the  body,  these  are  not  manifested.  The  parts  ex- 
clusively supplied  by  Sympathetic  trunks  do  not  appear  to  be  in  the 
least  degree  sensible ;  and  no  sign  of  pain  is  given  when  the  Sympa- 
thetic trunks  themselves  are  irritated.  But  in  certain  diseased  conditions 
of  those  organs,  violent  pains  are  felt  in  them ;  and  these  pains  can 
only  be  produced  through  the  medium  of  fibres  communicating  with  the 
sensorium  through  the  spinal  nerves. 


GENERAL  AND   SPECIAL   SENSATIONS.  529 

929.  It  is  difficult  to  speak  with  any  precision,  as  to  the  functions 
of  the  Sympathetic  system.  There  is  much  reason  to  believe,  how- 
ever, that  it  constitutes  the  channel  through  which  the  passions  and 
emotions  of  the  mind  affect  the  Organic  functions ;  and  this  especially 
through  its  power  of  regulating  the  calibre  of  the  arteries.  We  ha've" 
examples  of  the  influence  of  these  states  upon  the  Circulation,  in  the 
palpitation  of  the  heart  which  is  produced  by  an  agitated  state  of  feel- 
ing ;  in  the  Syncope,  or  suspension  of  the  heart's  action,  which  some- 
times comes  on  from  a  sudden  shock ;  in  the  acts  of  blushing '  and 
turning  pale,  which  consist  in  the  dilatation  or  contraction  of  the  small 
arteries ;  in  the  sudden  increase  of  the  salivary,  lachrymal,  and  mam- 
mary secretions,  under  the  influence  of  particular  states  of  mind,'  which 
increase  is  probably  due  to  the  temporary  dilatation  of  the  arteries  that 
supply  the  glands,  as  in  the  act  of  blushing ;  and  in  many  other  phe- 
nomena. It  is  probable  that  the  Sympathetic  system  not  only  thus 
brings  the  Organic  functions  into  relation  with  the  Animal,  but  that  it 
also  tends  to  harmonize  the  former  with  each  other,  so  as  to  bring  the 
various  acts  of  secretion,  nutrition,  &c.,  into  mutual  conformity.  For 
whilst  the  quantity  of  a  secreted  product,  or  the  amount  of  tissue  gene- 
rated in  a  part,  may  be  affected  by  an  increase  or  diminution  in  the 
calibre  of  the  vessels  supplying  it,  the  quality  of  the  secretion,  or  the 
character  of  the  tissue,  may  be  likewise  affected  (there  seems  valid 
reason  to  believe)  by  that  Nervous  force,  whose  relations  to  the  Physical 
and  Chemical,  as  well  as  to  all  other  Vital  forces,  are  so  intimate 
(§  396). 


CHAPTER  XIII. 


1.    Of  Sensation  in  general. 

930.  All  beings  of  a  truly  Animal  Nature  possess  (there  is  good 
reason  to  believe),  a  consciousness  of  their  own  existence,  first  derived 
from  a  feeling  of  some  of  the  corporeal  changes  taking  place  within 
themselves  ;  and  also  a  greater  or  less  amount  of  sensibility  to  the  con- 
dition of  external  things.  This  colisciousness  of  what  is  taking  place 
within  and  around  the  individual,  is  all  derived  from  impressions  made 
upon  its  ^afferent  nervous  fibres  ;  which,  being  conveyed  by  them  to  the 
central  sensorium,  are  there  felt  (§  390).  Of  the  mode  in  which  the 
impression,  hitherto  a  change  of  a  physical  character,  is  there  made  to 
act  upon  the  mind,  we  are  absolutely  ignorant;  we  only  know  the 
fact.  Although  we  commonly  refer  our  various  sensations  to  the  parts 
at  which  the  impressions  are  made, — as,  for  instance,  when  we  say 
that  we  have  a  pain  in  the  hand,  or  an  ache  in  the  leg, — we  really  use 
incorrect  language;  for,  though  we  may  refer  our  sensations  to  the 

34 


530  OF  SENSATION  IN   GENERAL. 

parts  where  the  impression  is  first  made  on  the  nerves,  they  are  really 
felt  in  the  brain.  This  is  evident  from  two  facts ; — first,  that  if  the 
nervous  communication  between  the  part  and  the  brain  be  interrupted, 
no  impressions,  however  violent,  can  make  themselves  felt ;  and  second, 
that  if  the  trunk  of  the  nerve  be  irritated  or  pinched,  anywhere  in  its 
course,  the  pain  which  is  felt  is  referred,  not  to  the  point  injured,  but 
to  the  surface  to  which  these  nerves  are  distributed.  Hence  the  well- 
known  fact  that,  for  some  time  after  the  amputation  of  a  limb,  the 
patient  feels  pains,  which  he  refers  to  the  fingers  or  toes  that  have  been 
removed ;  this  continues  until  the  irritation  of  the  cut  extremities  of  the 
nervous  trunks  has  subsided. 

931.,  It  would  seem  probable  that,  among  the  lower  tribes  of  Ani- 
mals, there  exists  no  other  kind  of  sensibility,  than  that  termed  general 
or  common;  which  pervades,  in  a  greater  or  less  degree,  nearly  every 
part  of  the  bodies  of  the  higher.  It  is  by  this,  that  we  feel  those  im- 
pressions, made  upon  our  bodies  by  the  objects  around  us,  which  pro- 
duce the  various  modifications  of  pain,  the  sense  of  contact  or  resistance, 
the  sense  of  variations  of  temperature,  and  others  of  a  similar  character. 
From  what  was  formerly  stated  {§  403)  of  the  dependence  of  the  im- 
pressibility/ of  the  sensory  nerves,  upon  the  activity  of  the  circulation 
in  the  neighbourhood  of  their  extremities,  it  is  obvious  that  no  parts 
destitute  of  blood-vessels  can  receive  such  impressions,  or  (in  common 
language)  can  possess  sensibility.  Accordingly  we  find  that  the  hair, 
nails,  teeth,  cartilages,  and  other  parts  that  are  altogether  extra-vascu- 
lar, are  themselves  destitute  of  sensibility ;  although  certain  parts  con- 
nected with  them,  such  as  the  bulb  of  the  hair,  or  the  vascular  membrane 
lining  the  pulp-cavity  of  the  tooth,  may  be  acutely  sensitive.  Again, 
in  tendons,  ligaments,  fibro-cartilages,  bones,  &c.,  whose  substance  con- 
tains very  few  vessels,  there  is  but  a  very  low  amount  of  sensibility. 
On  the  other  hand,  the  skin  and  other  parts,  which  are  peculiarly 
adapted  to  receive  such  impressions,  are  extremely  vascular ;  and  it  is 
interesting  to  observe,  that  some  of  the  tissues  just  mentioned  become 
acutely  sensible,  when  new  vessels  form  in  them  in  consequence  of 
diseased  action.  It  does  not  necessarily  follow,  however,  that  parts 
should  be  sensible  in  a  degree  proportional  to  the  amount  of  blood  they 
may  contain ;  for  this  blood  may  be  sent  to  them  for  other  purposes, 
and  they  may  contain  but,  a  small  number  of  sensory  nerves.  Thus, 
although  it  is  a  condition  necessary  to  the  action  of  Muscles,  that  they 
should  be  copiously  supplied  with  blood  (§  359),  they  are  by  no  means 
acutely  sensible ;  and,  in  like  manner,  Glands,  which  receive  a  large 
amount  of  blood  for  their  peculiar  purposes,  are  far  from  possessing  a 
high  degree  of  sensibility. 

932.  But  besides  the  general  or  common  sensibility,  which  is  dif- 
fused over  the  greater  part  of  the  body,  in  most  animals,  there  are  cer- 
tain parts,  which  are  endowed  with  the  property  of  receiving  impres- 
sions of  a  peculiar  or  special  kind,  such  as  sounds  or  odours,  that  would 
have  no  influence  on  the  rest ;  and  the  sensations  which  these  excite, 
being  of  a  kind  very  difi*erent  from  those  already  mentioned,  arouse 
ideas  in  our  minds,  which  we  should  never  have  gained  without  them. 
Thus,  although  we  can  acquire  a  knowledge  of  the  shape  and  position 


GENERAL  AND   SPECIAL   SENSATIONS.  531 

of  objects  by  the  touch,  we  could  form  no  notion  of  their  colour  with- 
out sight,  of  their  sounds  without  hearing,  or  of  their  odours  without 
smell.  The  nerves  which  convey  these  special  impressions,  as  already 
mentioned,  are  not  able  to  receive  those  of  a  common  kind ;  thus  the 
eye,  however  well  fitted  for  seeing,  would  not  feel  the  touch  of  the 
finger,  if  it  were  not  supplied  by  branches  from  the  Fifth  pair,  as  well 
as  by  the  Optic.  Nor  can  the  difierent  nerves  of  special  sensation  be 
affected  by  impressions  that  are  adapted  to  operate  on  others ;  thus  the 
ear  cannot  distinguish  the  slightest  difi*erence  between  a  luminous  and 
a  dark  object ;  nor  could  the  eye  distinguish  a  sounding  body  from  a 
silent  one,  except  when  the  vibrations  can  be  seen.  But  Electricity 
possesses  the  remarkable  power,  when  transmitted  along  the  several 
nerves  of  special  sense,  of  exciting  the  sensations  peculiar  to  each ;  and 
thus,  by  proper  management,  this  single  agent  may  be  made  to  produce 
flashes  of  light,  distinct  sounds,  a  phosphoric  odour,  a  peculiar  taste, 
and  a  pricking  feeling,  in  the  same  individual,  at  one  time.  Each  kind 
of  sensation  may  also  be  excited,  however,  by  mechanical  irritation  of 
the  nerve  which  is  subservient  to  it. — The  feeling  of  pain  may  be  in- 
duced by  impressions  made  upon  the  nerves  of  special  sense,  as  well  as 
upon  those  of  feeling,  if  these  impressions  be  too  violent  or  excessive. 
Thus  the  dazzling  of  the  eye  by  a  strong  light,  and  still  more,  the 
action  of  a  moderate  light  in  an  irritable  state  of  the  retina, — sudden 
loud  sounds,  or  even  sounds  of  moderate  intensity  but  of  peculiar  harsh- 
ness,— powerful  odours,  even  such  as  are  agreeable  in  moderation, — 
produce  feelings  of  uneasiness,  which  may  be  properly  called  painful, 
even  though  they  are  different  from  those  excited  through. the  nerves  of 
common  sensation. 

933.  As  a  general  rule,  it  may  be  stated,  that  the  violent  excite- 
ment of  any  sensation  is  disagreeable ;  even  when  the  same  sensation, 
experienced  in  a  moderate  degree,  may  be  a  source  of  extreme  pleasure. 
But  the  question  of  degree  is  relative  rather  than  absolute :  that  is,  a 
sensation  may  be  felt  as  extremely  violent  by  one  individual,  whilst 
another,  who  is  more  accustomed  to  sensations  of  the  same  kind,  is  not 
disagreeably  affected  by  it.  Thus,  our  sensations  of  heat  and  cold  are 
entirely  governed  by  the  previous  condition  of  the  parts  affected ;  as  is 
shown  by  the  well-known  experiment  of  putting  one  hand  in  hot  water, 
the  other  in  cold,  and  then  transferring  them  both  to  tepid  water, — 
which  will  seem  cool  to  the  one  hand,  and  warm  to  the  other.  The 
same  is  the  case  in  regard  to  light  and  sound,  smell  and  taste.  A  per- 
son going  out  of  a  totally  dark  room,  into  one  moderately  bright,  is  for 
the  time  painfully  impressed  by  the  light,  but  ^oon  becomes  habituated 
to  it ;  whilst  another,  who  enters  it  from  a  room  brilliantly  illuminated, 
will  consider  it  dark  and  gloomy. 

934.  The  intensity  with  which  sensations  are  felt,  therefore,  depends 
upon  the  degree  of  change  which  they  produce  in  the  sensorium.  The 
more  frequent  the  recurrence  of  any  particular  sensation,  the  more 
does  the  system  become  adapted  to  it,  and  the  less  change  does  it  pro- 
duce. It  is,  therefojre,  perceived  in  a  less  and  less  degree,  and  at  last 
it  ceases  to  excite  attention.  The  stoppage  of  a  constantly-recurring 
sensation,  however,  will  produce  a  change,  which  makes  as  strong  an 


532  OF   SENSATION  IN   GENERAL. 

impression  on  the  system  as  its  first  commencement ;  thus  there  are 
persons,  who  have  become  so  habituated  to  the  sound  of  a  waterfall  or 
even  of  a  forge-hammer,  that  they  cannot  sleep  anywhere  but  in  its' 
vicinity ;  and  it  is  well  known  that,  when  a  person  has  gone  to  sleep 
unde^  the  influence  of  some  continuous  or  frequently-recurring  sound 
(such  as  the  voice  of  a  reader,  the  dropping  of  water,  the  tread  of  a 
sentinel,  &c.),  the  cessation  of  the  sound  will  cause  his  awaking. 

935.  The  acuteness  of  particular  sensations  is  influenced  in  a  re- 
markable degree,  by  the  attention  they  receive  from  the  mind.  If  the 
mind  be  entirely  inactive,  as  in  profound  sleep,  no  sensation  whatever 
is  produced  by  very  feeble  impressions ;  on  the  other  hand,  when  the 
mind  is  from  any  cause  strongly  directed  upon  them,  impressions  very 
feeble  in  themselves  produce  sensations  of  even  painful  acuteness.  It 
is  in  this  manner,  that  the  habit  of  attending  to  sensations  of  any  par- 
ticular class  increases  their  vividness;  so  that  they  are  at  once  per- 
ceived by  an  individual  on  the  watch  for  them,  when  they  do  not  ex- 
cite the  observation  of  others.  We  may  even,  by  a  strong  effort,  direct 
the  mind  into  one  particular  channel,  so  as  to  receive  only  those  sensa- 
tions which  have  reference  to  it,  and  to  be  unconscious  quoad  all  others. 
Thus,  the  application  of  the  mind  to  some  particular  train  of  thought 
may  prevent  our  being  conscious  of  anything  that  is  going  on  around  or 
within  us, — the  conversation  of  friends, — the  striking  of  the  clock, — 
the  calls  of  hunger,  &c.  This  abstraction  may  be  altogether  voluntary ; 
.and  the  possession  of  the  power  of  thus  withdrawing  the  mind  at  will 
from  the  influence  of  external  disturbing  causes,  and  of  fixing  it  upon 
any  particular  .train  of  ideas,  is  an  extremely  valuable  one.  But  it  may 
also  be  involuntary,  and  may  be  a  source  of  inconvenience  from  its 
tendency  to  recur  at  improper  times, — ^producing  the  habitual  state 
which  is  known  as  absence  of  mind  or  reverie. 

936.  It  is  desirable  that  we  should  make  a  distinction,  between  the 
sensations  themselves,  and  the  ideas  which  are  the  immediate  results  of 
those  sensations,  when  they  are  perceived  by  the  mind.  These  ideas 
relate  to  the  cause  of  the  sensation,  or  the  object  by  which  the  impres- 
sion is  made.  Thus,  the  formation  of  the  picture  of  an  object,  upon 
the  retina,  produces  a  certain  impression  upon  the  optic  nerve ;  which, 
being  conveyed  to  the  sensorium,  excites  a  corresponding  sensation, 
with  which,  in  all  ordinary  cases,  w^e  immediately  connect  an  idea  of 
the  nature  of  the  object.  So  closely,  indeed,  is  this  idea  usually  re- 
lated to  the  sensation,  that  we  are  not  in  the  habit  of  making  a  distinc- 
tion between  them.  Thus,  I  may  say  at  this  moment,  ''  I  see  u  book 
on  the  table  before  me  ;"  ihe  fact  being,  that  I  am  conscious  of  a  certain 
picture,  which  conveys  to  my  mind  the  ideas  of  a  book  and  of  a  table, 
and  of  their  relative  positions ;  these  ideas  being  (in  Man)  the  result  of 
experience  and  associations, — in  fact,  originating  in  the  immediate 
application  of  the  knowledge  we  have  previously  acquired,  that  a  cer- 
tain object,  whose  picture  we  see,  is  a  book,  another  object  a  table,  and 
so  on.  We  are  liable  to  be  deceived  on  this  assumption ;  as  when,  by 
a  clever  imitation,  a  picture  on  a  plane  surface  is  ii^de  to  represent  an 
object  in  relief,  so  perfectly  as  at  once  to  excite  the  idea  of  the  latter. 


INTUITIVE  AND  ACQUIKED  PERCEPTIONS.  538 

— whioh  may  not  be  corrected,  until  we  have  ascertained  by  the  touch, 
the  flatness  of  the  real  object. 

937.  This  production  of  ideas,  by  the  agency  of  sensations,  is  a  pro- 
cess altogether  mental,  and  dependent  upon  the  laws  of  Mind.  We 
find  that  some  of  these  perceptions  or  elementary  notions  are  intuitive : 
that  is,  they  are  prior  to  all  experience,  and  are  as  necessarily  connected 
with  the  sensation  which  produces  them,  as  reflex  movements  are  with 
the  impression  that  excites  them.  This  seems  to  be  the  case,  for 
example,  with  regard  to  erect  vision.  There  is  no  reason  whatever  to 
think,  that  either  infants  or  any  of  the  lower  animals  see  objects  in  an 
inverted  position,  until  they  have  corrected  their  notion  by  the  touch ; 
for  there  is  no  reason  why-  the  inverted  picture  on  the  retina  should 
give  rise  to  the  idea  of  the  inversion  of  the  object.  The  picture  is  so 
received  by  the  mind,  as'  to  convey  to  us  an  idea  of  the  position  of 
external  objects,  which  harmonizes  with  the  ideas  we  derive  through  the 
touch ;  and  whilst  we  are  in  such  complete  ignorance  of  the  manner  in 
which  the  mind  becomes  conscious  of  the  sensation  at  all,  we  need  not 
feel  any'  difiiculty  about  the  mode  in  which  this  conformity  is  eff"ected. 
But  in  Man,  as  already  stated,  the  attaching  definite  ideas  to  certain 
groups  of  lines,  colours,  &c.,  with  respect  to  the  objects  they  represent, 
is  a  subsequent  process,  in  which  experience  and  memory  are  essentially 
concerned ;  as  we  see  particularly  well,  in  cases  presently  to  be  referred 
to,  in  which  the  sense  of  sight  has  been  acquired  comparatively  late  in 
life,  and  in  which  the  mode  of  using  it,  and  of  connecting  the  sensa- ' 
tions  received  through  it  with  those  received  through  the  touch,  has 
had  to  be  learned,  by  a  long-continued  training.  The  elementary 
notions  thus  formed, — which  may,  by  long  habit,  present  themselves  as 
immediately  and  unquestionably,  as  if  they  were  intuitive, — are  termed 
acquired  perceptions. 

938.  It  is  probable  that,  among  tlie  lower  animals,  the  proportion  of 
intuitive  perceptions  is  much  greater  than  in  Man ;  whilst,  on  the  other 
hand,  his  power  of  acquiring  perceptions  is  much  greater  than  theirs. 
So  that,  whilst  the  young  of  the  lower  animals  very  soon  becomes  pos- 
sessed of  all  the  knowledge  which  is  necessary  for  the  acquirement  of 
its  food,  the  construction  of  its  habitation^  &c.,  its  range  is  very  limited, 
and  it  is  incapable  of  attaching  any  ideas  to  a  great  variety  of  objects, 
of  which  the  Human  mind  takes  cognizance.  This  correspondence 
between  the  acquired  perceptions  of  Man,  and^the  intuitive  perceptions 
of  many  of  the  lower  animals,  is  strikingly  evident  in  regard  to  the 
power  of  measuring  distance.  This  is  acquired  very  gradually  by  the 
Human  infant,  or  by  a  person  who  has  first  obtained  the  faculty  of 
sight  later  in  life ;  but  it  is  obviously  possessed  by  many  of  the  lower 
animals,  to  whose  maintenance  it  is  essential,  immediately  upon  their 
entrance  into  the  world.  Thus,  a  Fly-catcher,  immediately  after  its 
exit  from  the  egg,  has  been  known  to  peck  at  and  capture  an  insect, — 
an  action  which  requires  a  very  exact  appreciation  of  distance,  as  well 
as  a  power  of  precisely  regulating  the  muscular  movements  in  accordance 
with  it. 


684  OF   SENSATION. 


2.    Of  the  Sense  of  Touch. 

939.  By  the  sense  of  Touch  is  usually  understood  that  modification 
of  the  common  sensibility  of  the  body,  of  which  the  surface  of  the  skin 
is  the  especial  seat,  but  which  exists  also  in  some  of  its  internal  reflexions. 
In  some  animals,  as  in  Man,  nearly  the  whole  exterior  of  the  body  is 
endowed  with  it,  in  no  inconsiderable  degree  ;  whilst  in  others,  as  the 
greater  number  of  Mammalia,  most  Birds,  Reptiles,  and  Fishes,  and  a 
large  proportion  of  the  Invertebrata,  the  greater  part  of  the  body  is  so 
covered  with  hairs,  scales,  bony  or  horny  plates,  shells  of  various  kinds, 
complete  horny  envelopes,  &c.,  as  to  be  nearly  insensible ;  and  the 
faculty  is  restricted  to  particular  portions  of  the  surface,  or  to  organs 
projecting  from  it,  which  often  possess  a  peculiarly  high  degree  of  this 
endowment.  Even  in  Man,  the  acuteness  of  the  sensibility  of  the 
cutaneous  surface  varies  greatly  in  diff*erent  parts,  being  greatest  at  the 
extremities  of  the  fingers  and  in  the  lips,  and  least  in  the  skin  of  the 
trunk,  arm,  and  thigh.  Thus  the  two  points  of  a  pair  of  compasses 
(rendered  blunt  by  bits  of  cork)  can  be  separately  distinguished  by  the 
point  of  the  middle  finger,  when  approximated  so  closely  as  l-3d  of  a 
line ;  whilst  they  require  to  be  opened  so  widely  as  30  lines  from  each 
other,  to  be  separately  distinguished,  when  pressed  upon  the  skin  over 
the  spine,  or  upon  that  of  the  middle  of  the  arm  or  thigh. 

940.  The  impressions  that  produce  the  sense  of  touch  are  received 
through  the  sensory  papillce,  with  which  the  surface  of  the  true  Skin  is 
beset, — more  or  less  closely,  according  to  the  part  of  it  that  is  examined. 
These  papillae  are  minute  elevations,  which  enclose  loops  of  capillary 
vessels  (Fig.  157),  and  branches  of  the  sensory  nerves.     With  regard 

Fig.  157. 


Capillary  network  at  margin  of  lips. 

to  the  precise  course  of  the  latter,  there  is  some  uncertainty;  but  it  is 
probable,  from  analogy,  that  the  representation  given  of  them  by 
Gerber  (Fig.  158)  is  in  the  main  correct ;  and  that  each  loop  of  the 
Sensory  nerve  is  connected  with  one  or  more  vesicular  foci,  on  some 
change  in  which  the  formation  of  the  sensory  impression  is  immediately 
dependent  (§  382).  It  is  peculiar  to  the  sense  of  Touch,  and  to  that  of 
Taste  (which  is  closely  related  to  it)  that  the  impression  must  be  made 
by  the  contact  of  the  object  itself  with  the  sensory  surface,  and  not 
through  any  intermediate  agency.  The  only  exception  to  this  is  in 
regard  to  the  sense  of  Temperature,  which  seems  to  be  in  many 
respects  different  from  ordinary  touch  ;  here  i\iQ  proximity  of  the  warm 


SENSE   OP  TOUCH.  535 

or  cold  body  is  sufficient,  the  impressions  being  made  after  the  manner 
of  those  of  odours,  sounds,  &c.  It  is  worth  remarking,  with  reference 
to  the  question  of  the  special  nature  of  the  sensory  fibres,  which  are  the 


Fig.  158. 

^^B^H 

^^^^B 

^^^^^^^^^^^B 

^^^^^^:(/ 

^^^^^^^^B^^^^HJ 

<i^'^^^^^'^^^^^^s5^5=^^^aM»^^^'°'^^V  ...■'.,  i^^JBbBSjiIu 

Distribution  of  the  tactile  nerves  at  the  extremity  of  the  Human  Thumb,  as  seen  in  a  thin  perpendicular 

section  of  the  skin. 

channel  of  these  impressions,  that  no  mechanical  irritation  of  the  nerves 
of  common  sensation  ever  seems  to  excite  sensations  of  heat  or  cold ; 
these  being  apparently  almost  as  distinct  from  the  sense  of  contact  as 
they  are  from  that  of  light  or  sound. 

941.  The  only  idea  communicated  to  our  minds,  when  this  sense  is 
exercised  in  its  simplest  form,  is  that  of  resistance;  and  we  cannot 
acquire  a  notion  of  the  size  or  shape  of  an  object,  or  of  the  nature  of 
its  surface,  through  this  sense  alone,  unless  we  move  the  object  over  our 
own  sensory  organ,  or  pass  the  latter  over  the  former.  By  the  various 
degrees  of  resistance  which  we  then  encounter,  we  form  our  estimate  of 
the  hardness  or  softness  of  the  body.  By  the  impressions  made  upon 
our  sensory  papillae,  when  they  are  passed  over  its  surface,  we  form  our 
idea  of  its  smoothness  or  roughness.  But  it  is  through  the  muscular 
sense,  which  renders  us  cognizant  of  the  relative  position  of  the  fingers, 
the  amount  of  movement  the  hand  has  performed  in  passing  over  the 
object,  and  of  other  impressions  of  like  nature,  that  we  acquire  our 
notions  of  the  size  and  figure  of  the  object ;  and  hence  we  perceive  that 
the  sense  of  touch,  without  the  power  of  giving  motion  to  the  tactile 
organ,  would  have  been  of  comparatively  little  use.  It  is  chiefly  in  the 
variety  of  movements  of  which  the  hand  of  Man  is  capable, — thus  con- 
ducive as  they  are,  not  merely  to  his  prehensile  powers,  but  to  the 
exercise  of  his  sensory  endowments, — that  it  ;s  superior  to  that  of  any 
other  animal ;  and  it  cannot  be  doubted  that  this  affords  us  a  very 
important  means  of  acquiring  information  in  regard  to  the  external 
world,  and  especially  of  correcting  m^ny  vague  and  fallacious  notions 
which  we  should  derive  from  the  sense  of  Sight,  if  used  alone.  On  the 
other  hand,  it  must  be  evident  that  our  knowledge  would  have  but  a 
very  limited  range,  if  this  sense  wer6  the  only  medium  through  which 
we  could  acquire  ideas.  Of  this  we  have  the  clearest  evidence  in  the* 
very  imperfect  development  of  the  mental  powers  in  those  unfortunate 
persons  who  have  suffered  under  the  deprivation  of  sight  and  hearing 
from  their  birth,  and  who  have  been  consequently  cut  off  from  the  most 
direct  means  of  profiting  by  the  knowledge  possessed  by  their  fellow- 
beings,  through  want  of  power  to  use  the  organs  of  speech.     It  is  only 


,-$86  OF   SENSATION. 

where  such  individuals  have  fallen  under  the  care  of  judicious  and  per- 
severing instructors,  that  their  mental  powers  have  been  called  into 
their  due  activity,  or  that  any  ideas  have  been  awakened,  beyond  those 
immediately  connected  with  the  gratification  of  the  animal  wants,  or 
with  painful  or  pleasurable  sensations.  Thus  a  mind,  quite  capable  of 
being  aroused  to  activity  and  enjoyment,  may  remain  in  a  condition 
nearly  allied  to  that  of  idiocy,  simply  for  want  of  the  sensations  requi- 
site to  produce  ideas  of  a  higher  and  more  abstract  character  than  those 
derived  tlirough  the  senses  of  Touch,  Taste,  and  Smell. 

942.  For  the  exercise  of  the  sense  of  Temperature,  the  integrity  of 
the  sensory  apparatus  contained  in  the  Skin  appears  to  be  requisite ; 
for  it  has  been  ascertained  by  the  recent  experiments  of  Prof.  Weber, 
that  if  the  integuments  'be  removed,  the"  application  of  hot  'or  cold 
bodies  only  causes  pain^  their  elevation  or  depression  of  temperature 
not  being  perceived ;  and  the  same  is  the  case  when  hot  or  cold  bodies 
are  applied  to  the  nerve-trunks.  It  is  worthy  of  note  that  there  are 
many  cases  on  record,  in  which  the  sense  of  Temperature  has  been  lost, 
while  the  ordinary  Tactile  sense  remained ;  and  the  former  is  sometimes 
preserved,  when  there  is  a  complete  loss  of  every  other  kind  of  sensi- 
bility. So  ^gain  we  find  that  the  subjective  sensations  of  temperature 
(that  is,  sensations  which  originate  from  changes  in  the  body  itself,  not 
from  external  impressions)  are  frequently  excited  quite  independently 
of  the  tactual  sensations ;  a  person  being  sensible  of  heat  or  of  chilliness 
in  soTue  part  of  his  body,  without  any  real  alteration  of  its  temperature, 
and  without  any  corresponding  affection  gf  the  tactual  sensations.  It 
is  cilrious  that  the  intensity  of  the  sensation  of  temperature  should 
depend,  not  merely  upon  the  relative  degree  of  heat  to  w^hich  the  part 
is  exposed  (§  933),"  but  also  upon  the  extend;  of  the  surface  over  which  it 
is  applied ;  a  weaker  impression  made  on  a  larger  surface  seeming  more 
powerful -than  a  stronger  impression  made  on  a  small  surface.  Thus, 
if  the  forefinger  of  one  hand  be  immersed  in  water  at  104°,  and  the 
whole  of  the  other  hand  be  plunged  in  water  at  102°,  the  cooler  water 
will  be  thought  the  warmer ;  whence  the  well-known  fact  that  water  in 
which  a  finger  can  be  held  without  discomfort,  will  produce  a  scalding 
sensation  when  the  entire  hand  is  immersed  in  it. 

3.    Of  the  Sense  of  Taste. 

943.  The  sense  of  Taste,  like  that  of  Touch,  is  excited  by  the  direct 
contact  of  particular  substances  with  certain  parts  of  the  body :  but  it 
IS  of  a  much  more  refined  nature  than  touch,  inasmuch  as  it  communi- 
cates to  us  a  knowledge  of  properties  which  that  sense  w^ould  not  reveal 
to  us.  All  substances,  however,  do  not  make  an  impression  on  the 
organ  of  Taste.  Some  have  a  strong  savour,  others  a  slight  one,  and 
others  are  altogether  insipid.  The  cause  of  these  differences  is  not 
altogether  understood ;  but  it  may  be  remarked  that,  in  general,  bodies 
which  cannot  be  dissolved  in  water,  alcohol,  &c.,  and  which  thus  cannot 
be  presented  to  the  gustative  papillae  in  a  state  of  solution,  have  no 
taste.  This  sense  has  for  its  chief  purpose  to  direct  animals  in  their 
choice  of  food ;  hence  its  organ  is  always  placed  at  the  entrance  to  the 


SENSE   OF   TASTE.  537 

digestive  canal.  In  higher  animals,  the  Tongue  is  the  principal  seat  of 
it ;  but  other  parts  of  the  mouth  are  also  capable  of  receiving  the 
impressioft  of  certain  savours.  The  mucous  membrane  which  covers  the 
tongue  is  copiously  supplied  with  papillae,  of  various  forms  and  sizes. 
Those  of  simplest  structure  closely  resembje  the  cutaneous  papillae ;  but 
there  are  others,  which  resemble  clusters  of  such  papillae,  each  being 
composed  of  a  fasciculus  of  looped  capillaries  (Fig.  159),  with  a  bundlb 

Fig.  159. 


Capillary  network  of  fungiform  papillae  of  the  Tongue. 

of  nerve-fibres,  whose  precise-  mode  of  termination  it  has  not  yet  been 
found  possible  to  ascertain.  These  fungifonn  papillae,  which  are 
covered  with  a  very  thin  epithelium,  are  probably  the  special  instru- 
ments of  the  sense  of  taste  ;  for  the  exercise  of  which  it  seems  probable 
that  the  sapid  substances  must  penetrate,  in  solution,  to  the  interior  of 
the  papilla.  When  these  papillae -are  called  into  action  by  the  contact 
of  substances  having  a  strong  savour,  they  not  unfrequently  become 
very  turgid,  by  a  distension  of  their  vessels  analogous  to  that  whicfh 
occurs  in  erection;  and  they  rise  up  from  the  surface  of  the  mucous 
membrane,  so  as  to  produce  a  decided  roughness  of  its  surface.  The 
conical  papillae,  on  the  other  hand,  are  furnished  with  thick  epithelial 
investments,  which  are  sometimes  prolonged  into  filamentous  appen- 
dages ;  and,  looking,  to  their  higher  development  among  other  animals, 
and  the  offices  to  which  they  are  there  subservient,  it  seems  probable 
that  their  functions  are  purely  mechanical,  and  that  they  serve  especially 
to  cleanse  the  teeth  from  adhering  particles.  The  nerve-fibres  can  be 
seen  to  form  distinct  loops  in  their  interior,  at  some  distance  from  the 
apex. 

944.  There  has  been  much  discrepancy  of  opinion  as  to  the  nerve 
which  is  specially  concerned  in  the  sense  of  Taste.  The  tongue  of  Man 
is  supplied  by  two  sensory  nerves  :  the  lingual  branch  of  the  Fifth  pair ; 
and  the  Glosso-pharyngeal.  The  former  chiefly  supplies  the  upper  sur- 
face of  the  front  of  the  tongue,  and  is  copiously -distributed  to  the 
papillae  near  the  tip.  The  latter  is  mostly  distributed  upon  the  mucous 
surface  of  the  Fauces,  and  upon  the  back  of  the  tongue ;  but  it  sends  a 
branch  forwards,  beneath  the  lateral  margin  on  each  side,  which  supplies 
the  edges  and  inferior  surface  of  the  tip  of  the  tongue,  and  'inosculates 
with  the  preceding.  There  is  reason  to  believe,  from  experiment,  that 
the  gustative  sensibility  of  the  tongue  is  not  destroyed  by  section  of 
either  of  these  nerves ;  though  the  operation  produces  a  total  or  partial 
loss  of  sensibility  over  certain  parts  of  the  surface.  There  seems  good 
reason  to  conclude,  that  the  lingual  branch  of  the  Fifth  pair  is  the 


538  OF   SENSATION. 

nerve,  through  which  the  sense  of  Taste,  as  well  as  that  of  Touch,  is 
exercised,  in  the  parts  of  the  tongue  to  which  it  is  specially  distributed, 
— which  are  those  that  possess  both  senses  in  the  most  acute  degree ; 
and  that  the  Glosso-pharyngeal  is  subservient  to  the  same  functions  in 
the  parts  supplied  by  it^  being  probably  the  exclusive  channel,  also, 
through  which  the  impressions  made  by  disagreeable  substances  taken 
into  the  mouth,  are  propagated  to  the  Medulla  Oblongata,  so  as  to  pro- 
duce nausea  and  excite  efforts  to  vomit.  The  latter  nerve  is  also,  as 
we  have  seen,  the  principal  channel  of  the  impressions  that  give  rise  to 
the  reflex  act  of  swallowing  ;  with  which  the  fifth  pair  is  concerned  in  a 
much  inferior  degree  (§  897). 

945.  A  considerable  part  of  the  impression  produced  by  many  sub- 
stances taken  into  the  mouth,  is  received  through  the  sense  of  Smell, 
rather  than  through  that  of  Taste.  Of  this,  any  one  may  easily  satisfy 
himself,  by  closing  the  nostrils,  and  breathing  through  the  mouth  only, 
whilst  holding  in  his  mouth,  or  even  rubbing  between  his  tongue  and  his 
palate,  some  aromatic  substance ;  its  taste  is  then  scarcely  recognised, 
although  it'  is  immediately  perceived  when  the  nasal  passages  are  re- 
opened, and  its  effluvia  are  drawn  into  them.  There  are  many  sub- 
stances, however,  which  have  no  aromatic  or  volatile  character ;  and 
whose  taste,  though  not  in  the  least  dependent  upon  the  action  of  the 
nose,  is. nevertheless  of  a  powerful  character.  Some  of  these  produce, 
by  irritating  the  mucous  membrane,  a  sense  of  pungency^  allied  to  that 
which  the  same  substances  (mustard,  for  instance)  will  produce,  when 
applied  to  the  skin  for  a  sufficient  length  of  time,  especially  if  the  Epi- 
dermis have  been  removed.  Such  sensations,  therefore,  are  evidently 
of  the  same  kind  with  those  of  Touch,  differing  from  them  only  in  the 
degree  of  sensibility  of  the  organ  through  which  they  are  received.  But 
there  are  others  which  produce  sensations  entirely  different  from  any 
that  can  be  received  through  the  skin,  and  which  are  properly  distin- 
guished, therefore,  as  gustative  ;  such  are  common  Salt,  which  may  be 
considered  as  a  type  of  the  saline  taste.  Sugar,  the  type  of  the  saccharine. 
Quinine  of  the  bitter,  and  Tannin  of  the  astringent,  and  Citric  acid  of 
the  sour.  All  such  substances,  therefore,  are  said  to  possess  sapid  pro- 
perties, exciting  distinctive  tastes,  quite  irrespectively  of  any  aromatic 
or  odoriferous  properties  which  they  may  also  possess,  as  well  as  of  their 
stimulating  action  on  the  skin. 

4.    Of  the  Sense  of  Smell. 

946.  Certain  bodies  possess  the  property  of  exciting  sensations  of  a 
peculiar  nature,  which  cannot  be  perceived  by  the  organs  of  taste  or 
touch,  but  which  seem  to  depend  upon  the  diffusion  of  the  particles  of 
the  substance  through  the  surrounding  air,  in  a  state  of  extreme  minute- 
ness. As  the  solubility  of  a  substance  in  liquid  seems  a  necessary  con- 
dition of  its  exciting  the  sense  of  Taste,  so  does  its  volatility,  or  tendency 
to  a  vaporous  state,  appear  requisite  for  its  having  Odorous  properties. 
Most  volatile  substances  are  more  or  less  odorous  :  whilst  those  which 
do  not  readily  transform  themselves  into  vapour,  usually  possess  little 
or  no  fragrance  in  the  liquid  or  solid  state,  but  acquire  strong  odorous 


SENSE   OF   SMELL.  639 

properties,  as  soon  as  they  are  converted  into  vapour, — by  the  aid  of 
heat  for  example.  There  are  some  solid  substances,  which  possess  very 
strong  odorous  properties,  without  losing  weight  in  any  appreciable 
degree  by  the  diffusion  of  their  particles  through  the  air.  This  is  the 
case,  for  example,  with  Musk ;  a  grain  of  which  has  been  kept  freely 
exposed  to  the  air  of  a  room,  whose  door  and  windows  were  constantly 
open,  for  a  period  of  ten  years ;  during  which  time  the  air,  thus  con- 
tinually changed,  was  completely  impregnated  with  the  odour  of  musk ; 
and  yet,  at  the  end  of  that  time,  the  particle  was  not  found  to  have  per- 
ceptibly diminished  in  weight.  We  can  only  attribute  this  result  to  the 
extreme  minuteness  of  the  division  of  the  odorous  particles  of  this  sub- 
stance. There  are  other  odorous  solids,  such  as  Camphor,  which  rapidly 
lose  weight  by  the  loss  of  particles  from  their  surface,  when  freely 
exposed  to  the  air. 

947.  The  conditions  of  the  sense  of  Smell  are  very  simple.  The  Ol- 
factory nerve  is  minutely  distributed  over  the  Schneiderian  membrane, 
which  is  itself  highly  vascular.  The  arrangement  of  the  ultimate  fibres 
of  this  nerve  has  not  been  ascertained.  The  Schneiderian  membrane 
is  kept  constantly  but  moderately  moist,  by  a  mucous  secretion  from  its 
surface  ;  and  this  condition  is  essential  to  the  acute  perception  of  odours. 
If  the  mucous  surface  be  too  dry,  as  happens  when  the  fifth  pair  is 

Fig.  160. 


The  Olfactory  nerve,  with  its  distribution  on  the  septum  nasi.  The  nares  have  been  divided  by  a  longitu- 
dinal s«*ction  made  immediately  to  the  left  of  the  septum,  the  right  nares  being  preserved  entire.  1.  The 
frontal  sinus.  2.  The  nasal  bone.  3.  The  crista  gall  i  process  of  the  ethmoid  bone.  4.  The  sphenoidal  sinus 
of  the  left  side.  5.  The  sella  turcica.  6.  The  basilar  process  of  the  sphenoid  and  occipital  bones.  7.  The 
posterior  openjng  of  the  right  nares.  8.  The  opening  of  the  Eustachian  tube  in  the  upper  part  of  the 
pharynx.  9.  The  soft  palate,  divided  through  its  middle.  10.  Cut  surface  of  the  hard  palate,  a.  The  olfac- 
tory peduncle,  b.  Its  three  roots  of  origin,  c.  Olfactory  ganglion,  from  which  the  filaments  proceed  that 
spread  out  in  the  substance  of  the  pituitary  membrane,  d.  The  nasal  nerve,  a  branch  of  the  ophthalmic 
nerve  descending  into  the  left  nares  from  the  anterior  foramen  of  the  cribriform  plate,  and  dividing  into 
its  external  and  internal  branch,  e.  The  naso-palatine  nerve,  a  branch  of  the  spheuo-palatine  ganglion 
distributing  twigs  to  the  mucous  membrane  of  the  septum  nasi  in  its  course  to  (/)  the  anterior  palatine 
foramen,  where  it  forms  a  small  gangliform  swelling  (Cloquet's  ganglion)  by  its  union  with  its  fellow  of  the 
opposite  side.  g.  Branches  of  the  nasopalatine  nerve  to  the  palate.  7i.  Posterior  palatine  nerves,  t,  i.The 
septum  nasi. 

paralysed,  the  sensation  is  blunted  or  even  destroyed ;  and  the  same 
effect  is  produced  by  the  presence  of  too  copious  a  secretion,  as  when 


540  OF   SENSATION. 

we  are  suffering  under  an  ordinary  cold. — The  highest  part  of  the  nasal 
fossae  appears  to  be  that,  in  which  there  is  the  most  acute  sensibility  to 
odours;  and  hence  it  is,  that,  when  we  snuff  the  air,  so.  as  to  direct  it 
into  this  portion  of  the  cavity,  we  perceive  delicate  odours,  which  would 
otherwise  have  escaped  us.  .The  acuteness  of  the  sense  of  Smell  depends, 
in  no  small  degree,  upon  the  extent  of  surface  exposed  by  the  membrane 
lining  the  nasal  cavity ;  and  in  this  respect  Mai\  is  far  surpassed  by 
many  of  the  lower  Mammalia,  especially  the  Ruminants,  which  are 
warned  by  its  means  of  the  proximity  of  their  enemies.  The  habit  of 
attention  to  sensory  impressions  of  this  class;  however,  very  much 
heightens  their  acuteness ;  hence  in  those  who  suffer  under  blindness  and 
deafness  conjointly,  it  is  usually  the  principal  means  by  which  indivi- 
duals are  distinguished,  and  the  presence  of  strangers  recognised;  and 
there  are  cases,  in  which  individuals  in  a  state  of  somnambulism  have 
exhibited  a  degree  of  acuteness  of  smell,  quite  comparable  to  that  which 
is  characteristic  of  Deer,  Antelopes,  &c. 

948.  Besides  ministering  to  the  sense  of  Smell,  by  stimulating  the 
secreting  powers  of  its  surface,  the  Fifth  pair  has  another  very  impor- 
tant function, — that  of  endowing  the  interior  of  the  nose  with  common 
sensibility,  and  thus  receiving  the  impression  produced  by  acrid  or  pun- 
gent substances,  which  act  upon  it  in  the  same  way  as  they  do  upon  the 
tongue.  Such  substances  are  felt,  by  the  irritation  they  produce,  rather 
than  smelt ;  and  the  sensation  they  occasion  gives  rise  to  the  consensual 
act  of  sneezing,  by  which  a  violent  blast  of  air  is  directed  through  the 
nasal  passages,  in  such  a  manner  as  to  clear  them  of  the  irritating  mat- 
ter, whether  solid  (as  snuff),  fluid,  or  gaseous.  Hence  this  action  may 
be  excited  by  the  contact  of  an  irritant  with  the  Schneiderian  mem- 
brane, after  the  olfactory  nerve  has  been  divided,  if  the  branches  of  the 
fifth  pair  be  entire ;  whilst  it  does  not  take  place  when  the  fifth  pair  is- 
paralysed,  even  though  the  sense  of  smell  is  retained. 

5.    Of  the  Sense  of  Hearing. 

949.  By  this  sense  we  become  acquainted  with  the  sounds  produced 
by  bodies  in  a  certain  state  of  vibration;  the  vibrations  being  propagated 
through  the  surrounding  medium,  by  the  corresponding  waves  or  undu- 
lations which  they  produce  in  it.  Although  air  is  the  usual  medium 
through  which  sound  is  propagated,  yet  liquids  or  solids  may  answer  the 
same  purpose.  On  the  other  hand,  no  sound  can  be  propagated  through 
a  perfect  vacuum. — It  is  a  fact  of  much  importance,  in  regard  to  the 
action  of  the  Organ  of  Hearing,  that  sonorous  vibrations  which  have 
been  excited,  and  are  being  transmitted,  in  a  medium  of  one  kind,  are 
not  imparted  with  the  same  readiness  to  others.  The  following  conclu- 
sions have  been  drawn  from  experimental  inquiries  on  this  subject. 

I.  Vibrations  excited  in  solid  bodies,  may  be  transmitted  to  water 
without  much  loss  of  their  intensity ;  although  not  with  the  same  readi- 
ness that  they  would  be  communicated  to  another  solid. 

II.  ^  On  the  other  hand,  vibrations  excited  in  water  lose  something  of 
their  intensity  in  being  propagated  to  solids ;  but  they  are  returned,  as 
it  were,  by  these  solids  to  the  liquid,  so  that  the  sound  is  more  loudly 


SENSE   OF   HEARING.  541 

heard  in  the  neighbourhood  of  these  bodies,  than  it  would  otherwise 
have  been. 

III.  The  sonorous  vibrations  are  much  more  weakened  in  the  trans- 
mission of  solids  to  air ;  and  those  of  air  make  but  little  impression  on 
solids.  ~ 

ly.  Sonorous  vibrations  in  water  are  transmitted  but  feebly  to  air  ; 
and  those  which  are  taking  place  in  air  are  with  difficulty  communicated 
to  water ;  but  the  communication  is  rendered  more  easy  by  the  inter- 
vention of  a  membrane  extended  between  them. 

The  application  of  these  conclusions,  in  the  Physiology  of  Hearing, 
will  be  presently  apparent. 

950.  It  is  on  the  Auditory  nerve  (commonly  termed  the  Portio 
Mollis  of  the  7th  pair),  that  the  sonorous  undulations  make  their  im- 
pression ;  but  we  invariably  find,  that  this  impression  is  made  through 
the  medium  of  a  liquid,  contained  in  a  cavity,  on  the  walls  of  which 
the  ultimate  branches  of  this  nerve  are  distributed.  The  simplest  form 
of  the  organ  of  Hearing,  such  as  we  find  in  Cephalopods  and  in  certain 
Fishes,  consists  merely  of  a  cavity  exxjavated  in  the  solid  framework 
of  the  head  ;  which  cavity  is  filled  with  liquid,  and  lined  by  a  membrane 
on  which  the  auditory  nerve  is  distributed.  These  animals  are  inhabi- 
tants of  the  water ;  and  the  sonorous  vibrations  excited  in  this  medium, ' 
being  communicated  to  the  solid  parts  of  the  head,  will  be  by  them 
again  transmitted  to  the  contained  fluid,  without  much  diminution  of 
their  intensity ;  according  to  principles  I.  and  II. — In  certain  Crustacea, 
however,  whose  organ  of  hearing  is  contained  in  the  base  of  the  anten- 
nae, as  well  as  in  most  Fishes,  we  find  the  auditory  cavity  or  vestibule 
no  longer  entirely  closed ;  but  having  an  aperture  on  its  external '  side, 
which  is  covered  in  by  a  membrane.  Here  the  vibrations  of  the  liquid 
within  the  cavity  will  be  more  directly  excited  by  those  of  the  sur- 
rounding medium,  for  if  this  be  water,  it  will  propagate  its  undulations 
into  the  cavity,  with  little  interruption  from  the  membrane  stretched 
across  its  mouth  ;  whilst,  if  it  be  air,  the  interposition  of  this  very  mem- 
brane will  greatly  assist  in  the  transmission  of  the  vibrations  to  the 
water  of  the  auditory  cavity,  according  to  principle  IV.  In  most  of  the 
animals  which  have  the  organ  of  hearing  constructed  upon  this  simple 
plan,  the  force  of  the  vibrations  of  the  fluid  within  the  cavity  is  increased 
by  several  minute  stony  concretions  (termed  otolithes),  which  are  sus- 
pended in  it.  These  act  according  to  principle  II.  Some  traces  of 
them  are  found  in  the  higher  animals ;  in  which  they  are  for  the  most 
part  superseded,  however,  by  an  apparatus  better  adapted  to  augment 
the  intensity  of  the  sonorous  vibrations. 

951.  This  apparatus  consists,  in  all  Vertebrated  animals  above  the 
inferior  Reptiles,  of  the  tympanum  or  drum,  with  its  membrane  "and 
chain  of  bones  ;  together  with,  in  the  Mammalia,  the  external  ear ; 
which  is  adapted  to  direct  itself,  more  or  less  completely,  towards  the 
point  from  which  the  sonorous  vibrations  proceed,  and  to  give  them  a 
degree  of  preliminary  concentration.  The  tympanic  apparatus  is 
interposed  between  the  external  ear  and  the  membrane  covering  the 
foramen  ovale,  which  is  the  entrance  to  the  real  auditory  cavity ;  and 
its  purpose  is  evidently,  to  receive  the  sonorous  vibrations  from  the  air, 


51^  OF   SENSATION. 

and  to  transmit  them  to  that  membrane,  in  such  a  manner  that  the 
vibrations  thus  excited  in  the  latter  may  be  much  more  powerful,  than 
they  would  be  if  the  air  acted  immediately  upon  it,  as  in  the  lower 
Vertebrata. — The  usual  condition  of  the  Membrana  Tympani  appears 
to  be  rather  lax ;  and,  when  in  this  condition,  it  vibrates  in  accordance 
"with  grave  or  deep  tones.  By  the  action  of  the  tensor  tympani  it  may 
be  tightened,  so  as  to  vibrate  in  accordance  with  sharper  or  higher 
tones ;  but  it  will  then  be  less  able  to  receive  the  impressions  of  deeper 
sounds.  This  state  we  may  easily  induce  artificially,  by  holding  the 
breath,  and  forcing  air  from  the  throat  into  the  Eustachian  tube,  so  as 
to  make  the  membrane  bulge  out  by  pressure  from  within ;  or  by  ex- 
hausting the  cavity  by  an  efibrt  at  inspiration,  with  the  mouth  and 
nostrils  closed,  which  will  cause  the  membrane  to  be  pressed  inwards 
by  the  external  air.  In  either  case,  the  hearing  is  immediately  found 
to  be  imperfect ;  but  the  deficiency  relates  only  to  grave  sounds,  acute 
ones  being  heard  even  more  plainly  than  before.  There  is  a  different 
limit  to  the  acuteness  of  the  sounds,  of  which  the  ear  can  naturally 
take  cognizance,  in  different  persons.  If  the  sound  be  so  high  in  pitch, 
that  the  membrana  tympani  cannot  vibrate  in  unison  wuth  it,  the 
individual  will  not  hear  it,  although  it  may  be  loud ;  and  it  has  been 
noticed,  that  certain  individuals  cannot  hear  the  very  shrill  tones  pro- 
duced by  particular  Insects,  or  even  Birds,  which  are  distinctly  audible 
to  others. 

952.  Not  only  do  we  find  the  tympanic  apparatus  superadded,  in 
the  higher  forms  of  the  organ  of  Hearing,  but  also  the  Semicircular 
Canals,  and  the  Cochlea. — The  former  exist  in  all  Vertebrata,  save  the 
lowest  ^Pishes ;  and  in  nearly  every  case,  they  are  three  in  number, 
and  lie  in  three  different  planes.  Hence  it  has  been  supposed,  with 
some  probability,  that  they  assist  in  producing  the  idea  of  the  direction 
of  sounds.  The  Cochlea  does  not  exist  at  all  in  Fishes  ;  and  in  Reptiles 
its  condition  is  quite  rudimentary.  In  Birds,  this  cavity  is  more  com- 
pletely formed,  though  the  passage  is  nearly  straight  instead  of  spiral ; 
of  its  real  character,  however,  there  can  be  no  doubt,  from  its  being 
divided,  like  the  cochlea  of  Man,  by  a  membranous  partition,  on 
which  the  ramifications  of  the  auditory  nerve  are  spread  out.  This 
appendage  has  been  supposed  to  be  the  organ  that  enables  us  to  judge 
of  the  pitch  of  sounds  ;  an  idea  which  derives  some  confirmation  from 
the  correspondence  between  the  development  of  the  cochlea  in  different 
animals,  and  the  variety  in  the  pitch  (or  length  of  the  scale)  of  the 
sounds  which  it  is  important  that  they  should  hear  distinctly,  espe- 
cially the  voices  of  their  own  kind. — That  the  Vestibule,  with  the 
passages  proceeding  from  it,  constitutes  the  true  organ  of  hearing,  even 
in  Man,  is  evident  from  the  fact,  that  when  (as  not  unfrequently 
happens)  the  tympanic  apparatus  has  been  entirely  destroyed  by 
disease,  so  as  to  reduce  the  organ  to  the  condition  of  that  in  which  no 
such  apparatus  exists,  the  faculty  of  Hearing  is  by  no  means  abolished, 
although  it  is  deadened. 

953.  The  faculty  of  Hearing,  like  other  senses,  may  be  very  much 
increased  in  acuteness  by  cultivation ;  but  this  improvement  depends 
rather  upon  the  habit  of  attention  to  the  faintest  impressions  made 


SENSE   OP   HEAKING. 


543 


upon  the  organ,  than  upon  any  change  in  the  organ  itself.  This  habit 
may  be  cultivated  in  regard  to  sounds  of  some  one  particular  class  ;  all 
others  being  heard  as  by  an  ordinary  person.  Thus,  the  watchful 
North  American  Indian  recognises  footsteps,  and  can  even  distinguish 

Fig.  161. 


A  diagram  of  the  Ear :— p.  The  pina.  t  The  tympanum.  I.  The  labyrinth.  1.  The  upper  part  of  the 
helix.  2.  The  antihelix.  3.  The  tragus.  4.  The  antitragus.  5.  The  lobulus.  6.  The  concha.  7.  The  upper 
part  of  the  fossa  scaphoidea.  8,  The  meatus.  9.  The  membrana  tympani,  divided  by  the  section.  10.  The 
three  little  bones,  crossing  the  area  of  the  tympanum,  malleus,  incus,  and  stapes;  the  foot  of  the  stapes 
blocks  up  the  fenestra  ovalis  upon  the  inner  wall  of  the  tympanum.  11.  The  promontory.  12.  The  fenestra 
rotunda;  the  dark  opening  above  the  ossicula  leads  into  the  mastoid  cells.  13.  The  Eustachian  tube;  the 
little  canal  upon  this  tube  contains  the  tensor  tympani  muscle  in  its  passage  to  the  tympanum.  14.  The 
vestibule.  15.  The  three  semicircular  canals,  horizontal,  perpendicular,  and  oblique.  16.  The  ampullae 
upon  the  perpendicular  and  horizontal  canals.  17.  The  cochlea.  18.  A  depression  between  the  convexities 
of  the  two  tubuli  which  communicate  with  the  tympanum  and  vestibule ;  the  one  is  the  scala  tympani, 
terminating  at  12;  the  other  is  the  scala  vestibuli. 

between  the  tread  of  friends  and  foes ;  whilst  his  white  companion, 
who  has  lived  among  the  busy  hum  of  cities,  is  unconscious  of  the 
slightest  sound.  Yet  the  latter  may  be  a  musician,  capable  of  dis- 
tinguishing the  tones  of  all  the  different  instruments  in  a  large  orches- 
tra, of  following  any  one  of  them  through  the  part  which  it  performs, 
and  of  detecting  the  least  discord  in  the  blended  effects  of  the  whole, — 
effects  which  would  be  to  the  unsophisticated  Indian  but  an  indistinct 
mass  of  sound.  In  the  same  manner,  a  person  who  has  lived  much  in 
the  country,  is  able  to  distinguish  the  note  of  every  species  of  bird 
that  lends  its  voice  to  the  general  chorus  of  nature  ;  whilst  the  inhabi- 
tant of  a  town  hears  only  a  confused  assemblage  of  shrill  sounds, 
which  may  impart  to  him  a  disagreeable  rather  than  a  pleasurable  sen- 
sation. 

954.  In  all  continued  sounds  or  tones,  there  are  several  points  to  be 
attended  to.  In  the  first  place,  we  take  cognizance  of  their  pitch; 
which  depends  upon  the  number  of  vibrations  in  a  given  time, — the 
high  notes  being  produced  by  the  most  rapid  vibrations,  and  the  low 
notes  by  the  slowest.    The  ear  can  appreciate  tones  produced  by  24,000 


544  OF  SENSATION. 

impulses  per  second,  the  pitch  of  which  is  about  four  octaves  above  the 
highest  F  of  the  piano-forte.  On  the  other  hand,  no  sequence  of  vibra- 
tions fewer  than  7  or  8  in  a  second,  can  produce  a  continuous  tone, 
because  the  impression  left  by  each  impulse  has  passed  away,  before  the 
next  succeeds ;  and  there  is  consequently  nothing  more  than  a  succession 
of  distinct  beats. — The  strength  or  loudness  of  musical  tones  depends 
(other  things  being  equal)  on  the  force  and  extent  of  the  vibrations,  com- 
municated by  the  sounding  body  to  the  medium  which  propagates  them. 
This  will  diminish,  however,  with  distance,  which  softens  loud  tones  by 
lowering  the  intensity  of  the  undulations,  as  a  consequence  of  their  more 
extensive  diffusion.  The  causes  of  the  difference  in  the  timbre^  or 
quality  of  musical  tones, — such,  for  instance,  as  those  which  exist 
between  the  tones  of  a  flute,  a  violin,  a  trumpet,  and  a  human  voice, 
all  sounding  a  note  of  the  same  pitch, — are  unknown :  but  they  pro- 
bably depend  upon  differences  of  form  in  the  undulations. — Our  ideas 
of  the  direction  and  distance  of  sounds,  are  for  the  most  part  formed  by 
habit.  Of  the  former  we  probably  judge  in  great  degree,  by  the  rela- 
tive intensity  of  the  impressions  received  by  the  two  ears ;  though  we 
may  form  some  notion  of  it  by  a  single  ear,  if  the  idea  just  stated  as 
to  the  use  of  the  semicircular  canals  (§  952),  be  correct. — Of  the  dis- 
tance of  the  sounding  body,  we  judge  by  the  intensity  of  the  sound, 
comparing  it  with  that  which  we  know  the  same  body  to  produce  when 
nearer  to  us.  The  Ear  may  be  deceived  in  this  respect  as  well  as  the 
eye  ;  thus  the  effect  of  a  full  band  at  a  distance  may  be  given  by  the 
subdued  tones  of  a  concealed  orchestra  close  by  us ;  and  the  Ventrilo- 
quist produces  his  deception,  by  imitating  as  closely  as  possible,  not 
the  sounds  themselves,  but  the  manner  in  which  they  would  strike  our 
ears. 

•  .  6.    Of  the  Sense  of  Sight. 

955..  By  the  faculty  of  Sight  we  are  made  acquainted,  in  the  first 
place,  with  the  existence  of  Light ;  and  by  the  medium  of  that  agent, 
we  take  cognizance  of  the  form,  size,  colour,  position,  &c.,  of  bodies 
that  transmit  or  reflect  it.  As  to  the  mode  in  which  luminous  impres- 
sions are  propagated  through  space,  philosophers  are  at  present  unde- 
termined ;  and  the  question  is  of  no  physiological  importance,  since  all 
are  agreed  as  to  the  laws  which  regulate  their  transmission.  These 
laws,  which  will  be  found  at  large  in  any  Treatise  on  Natural  Philoso- 
phy,* may  be  briefly  stated  as  follows. 

I.  Light  travels  in  straight  lines,  so  long  as  the  medium  through 
which  it  passes  is  of  uniform  density. 

II.  When  the  rays  of  light  pass  from  a  rarer  medium  into  a  denser 
one,  they  are  refracted  towards  a-  line  drawn  perpendicularly  to  the 
surface  they  are  entering. 

III.  When  the  rays  of  light  pass  from  a  .denser  medium  into  a  rarer 
one,  they  are  refracted  from  the  perpendicular. 

IV.  When  rays  proceeding  from  the  several  points  of  a  luminous 
object,  at  a  distance,  fall  upon  a  double  convex  lens,  they  are  brought 

*  See  Dr.  Golding  Bird's  Manual,  Chap.  XXII. 


SENSE  OF   SIGHT. 


545 


to  a  focus  upon  the  other  side  of  it ;  in  such  a  manner  that  an  inverted 
picture  of  the  object  is  formed  upon  a  screen,  placed  in  the  proper  posi- 
tion to  receive  it.     Thus  in  Fig.  162,  a  b  is  the  object,  and  E  F  the 

Fig.  162.  -    _ 


A. 


lens ;  the  rays  issuing  from  the  two  extremities  and  the  centre  of  the 
object,  are  brought  to  a  corresponding  focus  at  a  less  distance  on  the 
other  side  of  it,  so  as  to  form  a  distinct  picture ;  but  as  the  rays  from 
A  are  brought  to  a  focus  at  D,  and  those  from  B  at  c,  the  picture  will 
be  inverted. 

V.  The  further  the  object  is  removed  from  the  lens,  the  nearer  will 
the  picture  be  brought  to  it,  and  the  smaller  will  it  be. 

VI.  If  the  screen  be  not  held  precisely  in  the  focus  of  the  lens,  but 
a  little  nearer,  or  further  off,  the  picture  will  be  indistinct ;  for  the 
rays  which  form  it  will  either  not  have  met,  or  they  will  have  crossed 
each  other. 

956.  The  Eye,  in  its  most  perfect  form — such  as  it  possesses  in  Man 
and  the  higher  animals, — is  an  optical  instrument  of  wonderful  com- 
pleteness ;  designed  to  form  an  exact  picture  of  surrounding  objects 
upon  the  Retina  or  expanded  surface  of  the  Optic  nerve,  by  which  the 
impression  is  conveyed  to  the  brain.  The  rays  of  light,  which  diverge 
from  the  several  points  of  any  object,  and  fall  upon  the  front  of  the 
cornea,  are  refracted  by  its  convex  surface,  whilst  passing  through  it 
into  the  eye,  and  are  made  to  converge  slightly.  They  are  brought 
more  closely  together  by  the  crystalline  lens,  which  they  reach  after 
passing  through  the  pupil ;  and  its  refracting  influence,  together  with 
that  produced  by  the  vitreous  humour,  is  such  as  to  cause  the  rays,  that 
issued  from  each  point,  to  meet  in  a  focus  on  the  retina.  In  this 
manner,  a  complete  inverted  image  is  formed,  as  shown  in  Fig.  163 ; 
which  represents  a  vertical  section  of  the  eye,  and  the  general  course 

Fig.  163. 


of  the  rays  in  its  interior.  As  in  the  preceding  figure,  the  rays  which 
issue  from  the  point  A  are  brought  to  a  focus  at  D  ;  whilst  those  diverg- 
ing from  B  are  made  to  converge  upon  the  retina  at  c. — The  Retina, 
which  is  itself  so  thin  as  to  be  nearly  transparent,  is  spread  over  the 

85 


546  OF   SENSATION. 

layer  of  black  pigment,  which  lines  the  choroid  coat.  The  purpose  of 
this  is  evidently  to  absorb  the  rays  of  light  that  form  the  picture,  imme- 
diately after  they  have  passed  through  the  retina ;  in  this  manner,  they 
are  prevented  from  being  reflected  from  one  part  of  the  interior  of  the 
globe  to  another ;  which  would  cause  great  confusion  and  indistinctness 
in  the  picture.  Hence  it  is  that,  in  those  albino  individuals  (both  of 
the  Human  race,  and  among  the  lower  animals),  in  whose  eyes  this 
pigment  is  deficient,  vision  is  extremely  imperfect,  except  in  a  very 
feeble  light ;  for  the  Tascularity  of  the  choroid  and  iris  is  such  as  to 
give  to  these  membranes  a  bright  red  hue,  which  enables  them  power- 
fully to  reflect  the  light  that  reaches  the  interior  of  the  eye,  when  they 
are  not  prevented  from  doing  so  by  the  interposition  of  the  pigmentary 
layer. 

957.  The  Eye  is  so  constructed,  as  to  avoid  certain  errors  and  de- 
fects, to  which  all  ordinary  optical  instruments  are  liable.  One  of 
these  imperfections,  termed  spherical  aberration^  results  from  the  fact, 
that  the  rays  of  light,  passing  through  a  convex  lens  whose  curvature 
is  circular,  are  not  all  brought  to  their  proper  foci,  those  which  have 
passed  through  the  exterior  of  the  lens  being  made  to  converge  sooner 
than  those  which  have  traversed  its  central  portion.  The  result  of  this 
imperfection  is,  that  the  image  is  deficient  in  clearness,  unless  only 
the  central  part  of  the  lens  be  employed. — The  other  source  of  imper- 
fection is  what  is  termed  chromatic  aberration;  and  it  results  from  the 
unequal  degree  in  which  the  difierently-coloured  rays  are  refracted,  so 
that  they  are  brought  to  a  focus  at  different  points.  The  violet  rays, 
being  the  most  refrangible,  are  soonest  brought  to  a  focus ;  and  the  red 
being  the  least  refrangible,  have  their  focus  at  the  greatest  distance 
from  the  lens.  Hence  it  is  impossible  to  obtain  an  image  by  an  ordi- 
nary lens,  in  which  the  colours  of  the  object  are  accurately  repre- 
sented ;  for  the  foci  of  its  differently-coloured  portions  will  be  different ; 
and  its  white  rays  will  be  decomposed,  so  that  the  outlines  will  be  sur- 
rounded by  coloured  fringes. — The  Optician  is  enabled  to  correct  the 
effects  of  these  aberrations,  by  combining  lenses  of  different  densities 
and  curvatures ;  so  arranged  as  to  correct  each  other's  errors,  without 
neutralizing  the  refractive  power.  This  is  precisely  the  plan  adopted 
in  the  construction  of  the  Eye ;  which,  when  perfectly  formed,  and  in 
a  healthy  state,  forms  an  accurate  picture  of  the  object  upon  the  retina, 
free  from  either  spherical  or  chromatic  aberration.  This  is  effected  by 
the  combination  of  humours  of  different  densities,  having  curvatures 
precisely  adapted  to  the  required  purpose. 

958.  There  are  certain  variations,  however,  in  the  conformation  of 
the  eye  which  diminish  the  perfection  of  its  result.  Thus  the  Cornea 
may  be  too  convex,  and  the  .whole  refractive  power  too  great ;  so  that 
the  image  of  an  object  at  a  moderate  distance  is  formed  in  front  of  the 
retina,  instead  of  upon  it.  When  this  is  the  case,  a  distinct  image  can 
only  be  formed,  by  bringing  the  object  nearer  to  the  eye ;  the  effect  of 
w'hich  will  be,  to  throw  the  picture  further  back.  Such  an  eye  is  said 
to  be  myopic,  or  short-sighted ;  and  its  imperfection  may  be  corrected 
by  placing  a  concave  lens  in  front  of  the  cornea,  of  a  curvature  adapted 
to  neutralize  what  is  superfluous  in  the  convexity  of  the  latter. — On 


OF  THE  EYE  AS  AN  OPTICAL  INSTRUMENT.  547 

the  other  hand,  if  the  cornea  be  too  flat,  and  the  refractive  power  of 
the  humours  be  too  low,  the  convergent  rays  proceeding  from  an  object 
at  a  moderate  distance  will  not  meet  upon  the  retina,  but  behind  it  (if 
they  were  allowed  to  pass  on) ;  consequently,  the  picture  is  indistinct ;  and 
it  can  only  be  made  clear,  either  by  withdrawing  the  object  to  a  greater 
distance,  which  will  bring  the  focus  of  the  eye  nearer  to  its  front,  or 
by  interposing  a  convex  lens  to  increase  the  refractive  power  of  the  eye. 
Such  a  condition  is  termed  presbyopic  (from  its  being  common  in  aged 
persons),  or  long-sighted.  It  may  proceed  to  such  an  extent,  that  not 
even  the  removal  of  the  object  to  any  distance  can  permit  the  formation 
of  a  distinct  picture ;  so  that  the  assistance  of  a  convex  lens  must  be 
obtained  even  to  see  remote  objects  clearly ;  though  a  less  degree  of 
convexity  will  be  required,  than  for  the  clear  vision  of  nearer  objects. 
This  state  is  particularly  well  marked  after  the  operation  for  cataract ; 
for  the  removal  of  the  crystalline  lens  so  greatly  diminishes  the  refrac- 
tive power  of  the  eye,  as  to  render  necessary  the  assistance  of  convex 
lenses  of  high  curvature. 

959.  The  power,  by  which  a  healthy,  well-formed  eye  can  accommodate 
itself  to  the  distinct  vision  of  objects  at  varying  distances,  is  a  very  re- 
markable one  ;  and  its  rationale  is  not  yet  properly  understood.  Accord- 
ing to  the  laws  already  stated  (§  955,  V.  and  VI.)  the  picture  of  a  near 
object  can  only  be  distinct,  when  formed  more  remotely  from  the  lens 
than  the  picture  of  a  distant  object.  Consequently  when  the  eye,  that 
has  been  looking  at  a  distant  object,  and  has  seen  it  clearly,  is  turned 
to  a  near  object,  a  distinct  picture  of  the  latter  cannot  be  formed  without 
some  alteration,  either  in  the  distance  between  the  refractive  surfaces 
and  the  retina,  or  in  the  curvature  of  the  former.  It  seems  most  pro- 
bable that,  in  the  Human  eye,  this  adjustment  is  chiefly  effected  by  the 
automatic  contraction  of  the  ciliary  muscle ;  which,  by  drawing  the  lens 
nearer  to  the  iris,  will  thus  increase  its  distance  from  the  retina.  But 
this  may  not  be  the  sole  change. 

960.  The  various  humours  and  containing  membranes  of  the  Eye, 
thus  answer  the  purpose  of  a  most  delicate  and  self-adjusting  Optical 

Fig.  164. 


Distribution  of  Capillaries  in  vascular  layer  of  Retina. 


instrument ;  the  sole  part,  which  is  immediately  concerned  in  the  act 
of  sensation,  being  the  Retina,  or  net-like  expansion  of  the  Optic  nerve, 


648  OF   SENSATION. 

which  lies  between  the  black  pigment  and  the  vitreous  humour.  It  is 
in  this  structure,  that  the  presence  of  cells  at  the  peripheral  as  well  as 
the  central  extremities  of  the  afferent  nerves  (§  381),  may  be  most 
clearly  demonstrated.  They  can  scarcely  be  distinguished,  in  many 
animals,  from  the  cells  of  the  vesicular  matter  of  the  brain  ;  and,  like 
the  latter,  they  lie  in  the  midst  of  a  plexus  of  capillary  blood-vessels 
(Fig.  164),  which  supplies  the  materials  requisite  for  their  growth  and 
activity.  For  the  maintenance  of  the  due  nutrition  of  this  organ  it  is  re- 
quisite that  it  should  be  occasionally  called  into  use.  If  its  functional 
power  be  destroyed,  by  opacity  of  the  anterior  portion  of  the  eye,  the 
nutrition  of  the  retina  and  optic  nerve  suffers  to  such  a  degree  that 
these  parts  cease,  after  a  time,  to  exhibit  their  characteristic  structure ; 
thus  showing  that  the  general  rules  already  stated  (chap,  vii.)  in  regard 
to  the  connexion  between  the  functional  activity  and  the  due  nutrition, 
of  tissues  and  organs,  hold  good  with  respect  to  the  Nervous  structure. — 
The  fibres  of  the  Optic  nerve  when  they  diverge  to  form  the  Retina,  lose 
their  tubular  structure  ;  their  central  axes  only  being  continued,  in  the 
form  of  gray  fibres  (§  375),  and  some  of  these  becoming  directly  conti- 
nuous with  the  caudate  vesicles  (§  378). 

961.  The  picture  of  external  objects,  which  is  formed  upon  the 
Retina,  closely  resembles  that  which  we  see  in  a  Camera  Obscura.  It 
represents  the  outlines,  colours,  lights  and  shades,  and  relative  posi- 
tions, of  the  objects  before  us ;  but  these  do  not  necessarily  convey  to 
the  mind  the  knowledge  of  their  real  forms,  characters,  or  distances. 
The  perception  of  the  latter,  as  already  remarked  (§  936),  is  a  mental 
process;  and  it  may  be  intuitive^  or  acquired, — the  latter,  it  would 
seem,  being  the  general  condition  of  the  function  in  Man,  the  former  in 
the  lower  animals.  The  Infant  is  educating  his  perceptive  powers, 
long  before  any  indications  present  themselves,  of  the  exercise  of  higher 
mental  faculties.  By  the  combination,  especially,  of  the  sensations  of 
sight  and  touch,  he  is  learning  to  judge  of  the  surfaces  of  objects  as 
they  feel,  by  the  appearance  they  present, — to  form  an  idea  of  their 
distance,  by  the  mode  in  which  his  eyes  are  directed  towards  them, — 
and  to  estimate  their  size,  by-  combining  the  notions  obtained  through 
the  picture  on  the  retina,  with  those  he  acquires  by  the  movement  of 
his  hands  over  their  different  parts. — A  simple  illustration  will  show, 
how  closely  the  ideas  excited  by  the  two  sets  of  sensations,  are  blended 
in  our  minds.  The  idea  of  smoothness  is  one  which  has  reference  to 
the  touch ;  and  yet  it  constantly  occurs  to  us,  on  looking  at  a  surface 
which  reflects  light  in  a  particular  manner.  On  the  other  hand,  the 
idea  of  polish  is  essentially  visual,  having  reference  to  the  reflection  of 
light  from  the  surface  of  the  object;  and  yet  it  would  occur  to  us  from 
the  sensation  conveyed  through  the  touch,  even  in  the  dark. 

962.  That  this  sort  of  combination  is  not  intuitive  in  Man,  but  is  the 
result  of  experience,  is  evident  from  the  numerous  observations  made 
upon  those  who  had  acquired  the  sense  of  Sight  for  the  first  time,  after 
long  familiarity  with  the  characters  of  objects  as  perceived  through  the 
Touch.  Thus  a  boy  of  four  years  old,  upon  whom  the  operation  for 
congenital  cataract  had  been  very  successfully  performed,  continued  to 
find  his  way  about  his  father's  house,  rather  hj  feeli7ig  with  his  hands. 


SENSE   OF  VISION.  549 

as  he  had  been  formerly  accustomed  to  do,  than  by  his  newly-acquired 
sense  of  Sight ;  being  evidently  perplexed,  rather  than  assisted  by  the 
sensations  which  he  derived  through  it.  But  when  learning  a  new 
locality,  he  employed  his  sight  and  evidently  perceived  the  increase 
of  facility  which  he  derived  from  it.  Among  the  many  interesting 
particulars  recorded  of  the  youth  on  whom  Cheselden  operated  with 
equal  success,  it  is  mentioned  that,  although  perfectly  familiar  with  a 
dog  and  a  cat  by  feeling  them,  and  quite  able  to  distinguish  between  them 
by  his  sight,  it  was  long  before  he  associated  his  visual  with  his  tactual 
sensations,  so  as  to  be  able  to  name  either  animal  by  sight  alone. — The 
question  was  put  by  the  celebrated  Locke,  whether  a  person  born  blind, 
who  was  able  by  his  touch  to  distinguish  a  cube  from  a  sphere,  would, 
on  suddenly  obtaining  his  sight,  be  able  to  recognise  each  by  the  latter 
sense;  the  reply  was  given  in  the  negative ;  and  the  experience  of  the 
cases  just  referred  to,  as  well  as  of  many  others,  fully  justifies  such  an 
answer. 

963.  Still  there  are,  even  in  Man,  certain  intuitive  perceptions, 
which  afford  great  assistance  in  ther  formation  of  ideas  regarding  ex- 
ternal objects  through  the  visual  sense.  And  the  first  of  these  is  the 
power  by  which  we  recognise  their  erect  position,  notwithstanding  the 
inversion  of  the  image  upon  the  retina.  This  is  certainly  not  a  matter 
of  experience ;  nor  is  it  capable  of  explanation  (as  some  have  thought) 
by  a  reference  to  the  direction  in  which  the  rays  fall  upon  the  retina. 
It  is  the  mind  which  rectifies  the  inversion ;  and  as  already  remarked, 
it  is  just  as  difficult  to  understand  how  the  inverted  image  on  the  retina 
should  be  taken  cognizance  of  by  the  mind  at  all,  as  it  is  to  comprehend 
how  it  should  be  thus  rectified.  In  fact,  there  is  no  real  connexion 
whatever,  between  the  inversion  of  the  image  upon  the  retina,  and  that 
wrong  perception  of  external  objects,  which  some  have  thought  to  be 
its  necessary  consequence.  Any  distortion  of  the  picture,  giving  a 
wrong  view  of  the  relative  positions  of  the  objects  represented,  would  be 
attended  with  a  difierent  result. — The  same  may  be  said  of  the  cause  of 
the  singleness  of  the  sensation  perceived  by  the  mind,  although  an 
image  is  formed  upon  the  retina  of  each  ?ye,  of  those  objects  at  least, 
which  lie  in  the  field  of  vision  that  is  common  to  both.  This  blending 
of  the  pictures,  formed  upon  the  two  retinae,  into  a  single  perception, 
appears  to  be,  in  part  at  least,  the  eifect  of  habit.  For  when  the  images 
do  not  fall  upon  those  parts  of  the  two  retinae^ which  are  accustomed  to  act 
together,  double  vision  is  the  result.  Thus  if,  when  looking  steadily  at 
an  object,  we  press  one  of  the  eyeballs  sideways  with  the  finger,  we  see 
two  representations  of  the  object ;  and  the  same  thing  frequently  occurs, 
as  a  result  of  an  aff'ection  of  the  nerves  or  muscles  of  one  or  both  eyes 
(as  in  ordinary  strabismus  or  squinting),  or  from  some  change  in  the 
nervous  centres,  as  in  various  disorders  of  the  Encephalon,  and  in  in- 
toxication. If  this  condition  should  be  permanent,  however,  we  usually 
find  that  the  individual  becomes  accustomed  to  the  double  images,  or 
rather  ceases  to  perceive  that  they  are  double ;  probably  because  the 
mind  becomes  habituated  to  receive  the  impressions  from  the  two  parts 
of  the  retinae  which  now  act  together.  And  if,  after  the  double  vision 
has  passed  away,  the  conformity  of  the  two  eyes  be  restored  (as  by  the 


560  OP   SENSATION. 

operation  for  the  cure  of  squinting),  there  is  double  vision  for  some  little 
time,  although  the  two  parts  of  the  retinae,  which  originally  acted  toge- 
ther, are  now  brought  into  their  pristine  position. 

964.  But  the  images  thus  combined  are  far  from  being  identical ;  and 
one  of  the  most  remarkable  of  all  our  intuitive  perceptions,  is  that  by 
which  they  are  reconciled  and  combined,  and  are  caused  to  give  rise  to 
an  idea  that  differs  essentially  from  either  image.  No  near  object  can 
be  seen  by  the  two  eyes  in  the  same  manner ;  of  this  the  reader  may 
easily  convince  himself,  by  holding  up  a  thin  book,  in  such  a  position 
that  its  back  shall  be  in  a  line  with  the  nose,  and  at  a  moderate  distance 
from  it ;  and  by  looking  at  the  book,  first  with  one  eye,  and  then  with 
the  other.  He  will  find  that  he  gains  a  different  view  of  the  object  with 
each  eye,  when  used  separately ;  so  that  if  he  were  to  represent  it,  as 
he  actually  sees  it  under  these  circumstances,  he  would  have  two  per- 
spective delineations  differing  from  one  another,  because  drawn  from 
different  points.  But  on  looking  at  the  object  with  the  two  eyes  con- 
jointly, there  is  no  confusion  between  these  pictures ;  nor  does  the  mind 
dwell  upon  either  of  them  singly ;  but  the  union  of  the  two  intuitively 
gives  us  the  idea  of  a  solid  projecting  body, — such  an  idea  as  we  could 
only  have  otherwise  acquired  by  the  exercise  of  the  sense  of  touch. 
That  this  is  really  the  case,  has  been  proved  by  experiments  with  a  very 
ingenious  instrument,  the  Stereoscope,  invented  by  Prof.  Wheatstone ; 
which  is  so  contrived,  as  to  bring  to  the  two  eyes,  by  reflection  from 
mirrors,  two  different  pictures,  such  as  would  be  accurate  representa- 
tions of  a  solid  object,  as  seen  by  the  two  eyes  respectively.  When  the 
arrangement  is  such,  as  to  bring  the  images  of  these  pictures  to  those 
parts  of  the  retinae,  which  would  have  been  occupied  by  the  images  of 
the  solid  (supposing  that  to  have  been  before  the  eyes),  the  mind  will 
perceive,  not  one  or  other  of  the  single  representations  of  the  object, 
nor  a  confused  union  of  the  two,  but  a  body  projecting  in  relief,  the 
exact  counterpart  of  that  from  which  the  drawings  were  made. — Thus 
the  combination  of  the  two  pictures,  and  the  perception  of  an  object 
different  from  either  of  them,  is  effected  by  a  mental  process  of  an  in- 
stinctive kind,  of  the  nature  of  which  we  know  nothing  further. 

965.  When  two  pictures,  representing  dissimilar  objects,  are  pro- 
jected upon  the  retinae  of  the  two  eyes  by  means  of  the  Stereoscope,  the 
result  is  a  curious  one.  The  mind  perceives  only  one  of  them,  the 
other  being  completely  excluded  for  a  time ;  but  it  commonly  happens 
that,  after  one  has  been  seen  for  a  short  period,  the  other  begins  to 
attract  attention  and  takes  its  place,  the  first  entirely  disappearing ;  so 
that  there  is  no  confusion  or  intermingling  of  images,  except  at  the 
moment  of  change.  The  Will  may  determine,  to  a  certain  extent, 
which  object  shall  be  seen ;  but  not  entirely ;  for  if  one  picture  be  more 
illuminated  than  the  other,  it  will  be  seen  during  a  larger  proportion  of 
the  time. — An  interesting  variation  of  this  experiment  may  be  made, 
without  the  aid  of  the  Stereoscope,  by  holding  a  piece  of  blue  glass 
before  one  eye,  and  a  piece  of  yellow  glass  before  the  other.  The  re- 
sult will  be,  not  that  everything  will  be  seen  of  a  green  colour,  but  that 
the  surrounding-  objects  will  be  seen  alternately  blue  and  yellow;  or 
sometimes  the  field  of  vision  will  be  blue  spotted  with  yellow,  alterna- 


ESTIMATE   OF  DISTANCE   BY  VISION.  551 

ting  with  yellow  spotted  witli  blue.  Thus,  when  we  have  two  dissimilar 
objects  before  the  eyes,  our  attention  cannot  be  kept  upon  either,  to  the 
exclusion  of  the  other,  but  is  alternately  and  involuntarily  directed, 
either  in  part  or  completely,  to  one  and  the  other. 

966.  Our  idea  of  the  distance  of  near  objects  is  evidently  acquired 
from  experience ;  and  is  suggested  by  the  muscular  sensations  which 
are  produced  by  the  contraction  of  the  adductor  muscles  of  the  eyes. 
When  we  direct  our  eyes  towards  a  near  object,  a  certain  degree  of  con- 
vergence takes  place  between  their  axes ;  the  degree  increasing  as  the 
distance  between  the  object  and  the  eyes  diminishes ;  and  vice  versd. 
We  instinctively  interpret  the  sensations  thus  produced,  in  such  a 
manner  as  to  be  able  to  compare,  with  great  accuracy,  the  relative  dis- 
tances of  two  objects  that  are  not  remote  from  the  eyes.  This  intuition, 
however,  is  evidently  one  of  the  acquired  kind ;  as  may  be  seen  by 
watching  the  actions  of  an  infant,  or  of  a  person  who  has  recently  be- 
come possessed  of  Vision.  When  an  object  is  held  before  the  eyes,  and 
an  attempt  is  made  to  grasp  it,  the  manner  in  which  the  attempt  is  made 
clearly  shows,  that  there  is  no  power  of  forming  a  precise  idea  of  its 
situation,  such  as  that  which  exists  in  many  of  the  lower  animals  from 
their  first  entrance  into  the  world  (§  938).  The  impressions  made  upon 
the  eyes  have  to  be  corrected  by  those  received  through  the  touch,  be- 
fore the  power  of  judging  of  distance  is  acquired.  How  much  this 
power  depends  upon  the  conjoint  use  of  both  eyes,  is  evident  from  the 
difficulty  with  which  any  actions,  that  require  an  exact  appreciation  of 
distance,  are  performed  by  those  who  have  lost  the  sight  of  one  eye, 
until  they  have  acquired  new  modes  of  judging  of  it. 

967.  In  regard  to  remote  objects,  we  have  not  the  same  guide ;  since 
the  convergence  of  the  eyes,  in  viewing  them,  is  so  slight  that  the  axes 
are  virtually  parallel.  Our  judgment  of  their  distance  is  chiefly  founded 
upon  their  apparent  size,  if  their  actual  size  be  known  to  us ;  and  also 
upon  the  extent  of  ground,  which  we  see  to  intervene  between  ourselves 
and  the  object.  But  if  we  do  not  know  their  actual  size,  and  are  so 
situated  that  we  cannot  estimate  the  intervening  space,  we  form  our 
judgment  chiefly  from  the  greater  or  less  distinctness  of  their  colour  and 
outline.  Hence  our  idea  of  it  will  be  very  much  afi*ected  by  varying 
states  of  the  atmosphere ;  a  slight  haziness  increasing  the  apparent  dis- 
tance ;  whilst  a  peculiarly  clear  state  of  the  air  will  seem  to  cause  re- 
mote objects  to  approach  much  more  closely.  This  want  of  conver- 
gence between  the  axes  of  the  two  eyes,  has  the  further  effect  of  causing 
the  pictures  upon  the  two  retinae  to  be  nearly  identical ;  and  conse- 
quently the  idea  of  projection  is  not  so  strongly  excited ;  nor  are  we  able 
to  distinguish  with  the  same  certainty  between  a  well-painted  picture, 
in  which  the  lights  and  shades  are  preserved,  and  the  objects  themselves 
in  relief. 

968.  Our  notion  of  the  size  of  an  object  is  closely  connected  with 
that  of  its  distance.  It  is  founded  upon  the  dimensions  of  the  picture 
projected  on  the  retina ;  and  the  dimensions  of  this  picture  will  vary, 
according  to  the  laws  of  optics  (§  955)  inversely  as  the  distance, — 
being  for  example,  twice  as  great  when  the  object  is  viewed  at  the 
distance  of  one  foot  as  when  it  is  carried  to  the  distance  of  two  feet. 
When  we   know  the   relative   distances  of  two   objects,  the   estima- 


562  OP  SENSATION. 

tion  of  their  real  comparative  sizes  from  their  apparent  sizes  is  easily 
effected  by  a  simple  process  of  mind ;  but  this  is  not  the  case,  when  we 
only  guess  at  their  distances  ;  and  our  estimate  of  the  size  of  objects, 
even  moderately  remote,  is  as  much  affected  by  states  of  the  atmosphere 
as  that  of  their  distance, — the  one  being,  in  fact,  proportional  to  the 
other.  Thus  a  slight  mist,  which  gives  the  idea  of  increased  distance, 
will  also  augment  the  apparent  size ;  because  in  order  that  an  object 
two  miles  off,  should  produce  a  picture  upon  the  retina  of  the  same 
extent  with  that  made  by  an  object  one  mile  off,  it  must  have  double 
the  dimensions.  It  is  evident  that  our  perception  of  the  size  of  objects 
must  be  acquired  by  experience,  in  the  same  manner  as  that  of  their 
distance  has  been  shown  to  be. 

969.  We  have  now  to  consider  briefly  some  other  phenomena  of 
Vision,  in  which  the  acts  of  Mind,  that  have  been  just  alluded  to,  do 
not  participate. — The  contraction  of  the  Pupil,  under  the  stimulus  of 
light,  seems  to  be  effected  by  a  sphincter  muscle,  which  surrounds  the 
orifice,  and  which  is  put  in  action  by  a  branch  of  the  Third  pair  of 
nerves.  This  is  an  action  with  which  the  will  has  nothing  to  do  ;  and 
it  takes  place  entirely  without  our  consciousness.  Although  it  is  due 
to  the  stimulus  of  light,  yet  there  is  reason  to  believe  that  the  conscious- 
ness of  the  presence  of  light  is  not  requisite ;  and  that  it  is,  therefore, 
a  purely  reflex  action.  The  Optic  nerve  seems  to  be  the  channel 
through  which  the  impression  is  conveyed  to  the  nervous  centres ; 
whilst  the  Third  pair  is  that  through  which  the  motor  impulse  is  con- 
veyed to  the  iris ;  but  there  is  some  ground  for  the  idea  that  the  Fifth 
pair  may  in  some  degree  convey  the  requisite  stimulus,  when  the  optic 
nerve  has  been  divided.  That  the  dilatation  of  the  pupil  is  a  muscular 
action,  appears  probable  from  the  fact  that  the  radiating  fibres  of  the 
iris  are  of  the  same  character  with  the  circular;  both  sets  constituting, 
in  Man,  a  peculiar  variety  of  the  non-striated  form  of  muscular  tissue. 
Through  what  nervous  channel,  however,  the  stimulus  to  this  action  is 
conveyed,  has  not  yet  been  clearly  made  out.  The  contraction  of  the 
pupil  is  evidently  destined  to  exclude  from  the  interior  of  the  eye,  such 
an  amount  of  light  as  would  be  injurious  to  it ;  whilst  its  dilatation  in 
opposite  circumstances  admits  the  greatest  possible  number  of  rays. 
There  is  a  contraction  of  the  pupils,  however,  which  takes  place  without 
any  change  in  the  amount  of  light.  This  occurs  when  the  two  eyes  are 
made  to  converge  strongly  upon  any  object  brought  very  near  them ; 
and  its  purpose  appears  to  be,  to  prevent  rays  from  entering  the  eye 
at  such  a  wide  angle,  as  would  render  it  impossible  for  them  to  be  all 
brought  to  their  proper  foci,  and  would  thus  produce  an  indistinct 
image. 

970.  In  the  use  of  the  Eye,  like  that  of  the  Ear,  there  is  a  tendency 
to  blend  into  one  continuous  image  a  succession  of  luminous  impressions 
made  at  short  intervals ;  upon  which  fact  depend  a  number  of  curious 
optical  illusions.  The  length  of  the  greatest  interval  that  can  elapse 
without  an  interruption  of  the  presence  of  the  image  (in  other  words 
the  duration  of  the  visual  impression),  may  be  measured  by  causing  a 
luminous  object  to  whirl  round,  and  by  ascertaining  the  longest  period 
that  may  be  allowed  for  each  revolution,  consistently  with  the  complete- 


OF   THE   VOICE  AND   SPEECH. 


553 


ness  of  the  circle  of  light  thus  formed.  By  experiments  of  this  kind, 
the  time  has  been  found  to  vary,  in  different  individuals,  or  in  diffe- 
rent states  of  the  same  individual,  from  about  l-4th  to  1-lOth  of  a 
second :  that  is,  the  impression  must  be  repeated  from  four  to  ten  times 
in  each  second,  to  insure  the  continuousness  of  the  image. 

971.  The  impressions  of  variety  of  colour .^  are  produced  by  the  diffe- 
rently-coloured rays,  which  objects  reflect  or  transmit  to  the  eye.  It 
is  curious  that  some  persons,  whose  sight  is  perfectly  good  for  forms, 
distances,  &c.,  are  unable  to  discriminate  colours.  This  curious  affec- 
tion has  received  the  name  of  Daltonism ;  from  the  circumstance  that  the 
celebrated  Dalton  was  an  example  of  it.  There  are  numerous  modifi- 
cations of  it ;  the  want  of  power  to  discriminate  colour  being  total  in 
some  ;  whilst  in  others  it  extends  only  to  certain  shades  of  colour,  or  to 
the  complementary  colours. 

972.  When  the  retina  has  been  exposed  for  some  time  to  a  strong 
impression  of  some  particular  kind,  it  seems  less  susceptible  of  feebler 
impressions  of  the  same  kind ;  thus  if  we  look  at  any  brightly -luminous 
object,  and  then  turn  our  eyes  upon  a  sheet  of  paper,  we  shall  perceive 
a  dark  spot  upon  it ;  the  portion  of  the  retina,  which  had  received  the 
brighter  image,  not  being  affected  by  the  fainter  one. — Again,  when 
the  eyes  have  received  a  strong  impression  from  a  coloured  object,  the 
spot  which  is  seen  when  the  eyes  are  directed  upon  a  white  surface  ex- 
hibits the  complementary  colour  ;  for  the  retina  has  been  so  strongly 
affected,  in  the  part  that  originally  received  the  image,  by  its  vivid  hue, 
that  it  does  not  perceive  the  fainter  hue  of  the  same  kind  in  the  object 
to  which  it  is  then  turned,  and  it  is  impressed  only  by  the  remaining 
rays  forming  the  complementary  colours.  This  explanation  applies  to 
the  phenomena  of  the  coloured  shadows  which  are  often  seen  at  sunset, 
and  of  those  which  may  be  seen  in  a  room  whose  light  enters  through 
coloured  glass  or  drapery.  For  if  the  prevailing  light  be  of  one  colour, 
— orange  or  red  for  instance, — the  eye  will  not  take  cognizance  of  that 
colour  in  the  faint  light  of  the  shadows ;  and  will  see  only  its  comple- 
ment, blue  or  green.  If  the  shadow  be  viewed  through  a  tube,  in  such 
a  manner  that  the  general  coloured  ground  is  excluded,  it  presents  the 
ordinary  tint. 


CHAPTER  XIV. 


OF   THE   VOICE   AND   SPEECH. 


973.  There  is  one  particular  application  of  Muscular  power  in  Man, 
which  deserves  special  consideration,  as  being  that  by  which  he  effects" 
his  most  complete  and  intimate  communication  with  his  fellows ; — that, 
namely,  by  which  his  organ  of  Voice  is  put  into  action.  In  all  air- 
breathing  Vertebrata,  the  production  of  sound  depends  upon  the  pas- 
sage of  air  through  a  certain  portion  of  the  respiratory  tubes,  which  is 


554  OF  THE  VOICE  AND  SPEECH. 

SO  constructed  as  to  set  it  in  vibration,  as  it  passes  forth  from  the 
lungs. — In  Reptiles,  the  vibrating  apparatus  is  situated  at  the  point, 
where  the  trachea  opens  into  the  front  of  the  pharynx ;  it  is  of  very 
simple  construction,  however,  being  only  composed  of  a  slit  bounded 
by  two  contractile  lips ;  and  few  of  the  animals  of  this  class  can  pro- 
duce any  other  sound  than  a  hiss,  which,  owing  to  the  great  capacity 
of  their  lungs,  is  often  very  much  prolonged. — In  Birds,  the  situation 
of  the  vocal  organ  is  very  different.  The  trachea  opens  into  the  front 
of  the  pharynx,  as  in  Reptiles,  by  a  mere  slit ;  the  borders  of  which 
have  no  other  movement  than  that  of  approaching  one  another,  so  as 
to  close  the  aperture  when  necessary.  This  appears  to  be  the  instru- 
ment for  regulating  the  ingress  and  egress  of  air,  in  conformity  with 
the  wants  of  the  respiratory  function.  The  vocal  larynx  of  Birds  is 
situated  at  the  lower  extremity  of  the  trachea,  just  where  it  subdivides 
into  the  bronchial  tubes ;  and  it  is  of  very  complex  construction,  espe- 
cially in  the  singing  birds. — In  Mammalia,  on  the  other  hand,  the 
vocal  organ  and  the  regulator  of  the  respiration  are  united  in  one  la- 
rynx, which  is  situated  at  the  top  of  the  trachea.  There  are  few,  if 
any,  of  this  class,  which  have  not  some  vocal  sound ;  but  the  variety 
and  expressiveness  which  can  be  given  to  it,  differ  considerably  in  the 
several  orders ;  being  by  far  the  greatest  in  Man,  who  alone,  there  is 
reason  to  believe,  has  the  power  of  producing  articulate  sounds,  or  pro- 
per language, 

974.  The  Larynx  is  built-up,  as  it  were,  upon  the  Cricoid  cartilage 
(Fig.  165,  X  w  r  u),  which  surmounts  the  trachea,  and  which  might  be 

Fig.  165. 


Bird  s-eye  view  of  Larytix  from  above,  after  Willis:— o  e  h,  the  thyroid  cartilage,  embracing  the  ring  of 
me  cricoid  r  uxw,  and  turning  upon  the  axis  x  z,  which  passes  through  the  lower  horns;  n  f,  n  f,  the  ary- 
tenoid cartilages,  connected  by  the  arytenoideus  transversus ;  t  v,  T  v,  the  vocal  ligaments;  N  x,  the  right 
crico-arytenoideus  lateralis  (the  left  being  removed);  v  A/,  the  left  thyro-arytenoideus  (the  right  being  re- 
moved) ;  N  i,  N  i,  the  crico-arytenoidei  postici;  b  b,  the  crico-arytenoid  ligaments. 

considered  as  its  highest  ring  modified  in  form,  its  depth  from  above 
downwards  being  much  greater  posteriorly  than  anteriorly.  This  is 
embraced,  as  it  were,  by  the  Thyroid  cartilage  (a  E  h)  ;  which  is  arti- 


REGULATION   OF   THE   APERTURE   OF   THE   GLOTTIS.  555 

culated  to  the  sides  of  the  Cricoid  by  its  lower  horns,  round  the  extre- 
mities of  which  it  may  be  considered  to  rotate,  as  on  a  pivot.  In  this 
manner,  the  front  of  the  Thyroid  cartilage  may  be  lifted  up,  or  de- 
pressed, by  the  muscles  which  act  upon  it ;  whilst  the  position  of  its 
posterior  part  is  but  little  changed.  Upon  the  upper  surface  of  the 
back  of  the  Cricoid  cartilage,  are  seated  the  two  small  Arytenoid  carti- 
lages (n  f)  ;  these  are  so  tied  to  the  cricoid  by  a  bundle  of  strong  liga- 
ments (b  b),  as  to  have  a  sort  of  rotation  upon  an  articulating  surface, 
which  enables  them  to  be  approximated  or  separated  from  each  other, 
— their  inner  edges  being  nearly  parallel  in  the  first  case,  but  slanting 
away  from  each  other  in  the  second.  To  the  summit  of  these  cartilages 
are  attached  the  Chordce  vocales,  or  vocal  ligaments  (t  u)  composed  of 
yellow  fibrous  or  elastic  tissue.  These  stretch  across  to  the  front  of 
the  Thyroid  cartilage ;  and  it  is  upon  their  condition  and  relative  situ- 
ation, that  the  absence  or  the  production  of  vocal  tones,  and  all  their 
modifications  of  pitch,  depend.  They  are  rendered  tense  by  the  de- 
pression of  the  front  of  the  Thyroid  cartilage,  and  relaxed  by  its  ele- 
vation ;  by  which  action  the  pitch  of  the  tones  is  regulated.  But  for 
the  production  of  any  vocal  tones  whatever,  they  must  be  brought  into 
a  nearly  parallel  condition,  by  the  mutual  approximation  of  the  points 
of  the  arytenoid  cartilages  to  which  they  are  attached ;  whilst  in  the 
intervals  of  vocalization,  these  are  separated,  and  the  rima  glottidis,  or 
fissure  between  the  chordae  vocales,  assumes  the  form  of  a  narrow  V, 
with  its  point  directed  backwards. 

975.  Thus  there  are  two  sets  of  movements  concerned  in  the  act  of 
vocalization ; — the  regulation  of  the  relative  position  of  the  Vocal 
Cords,  which  is  efi*ected  by  the  movements  of  the  Arytenoid  cartilages ; 
— and  the  regulation  of  their  tension,  which  is  determined  by  the 
movements  of  the  Thyroid  cartilage.  The  Arytenoid  cartilages  are 
made  to  diverge  from  one  another  by  means  of  the  Crieo-arytenoidei 
postici  of  the  two  sides  (n  I,  N  I),  which  proceed  from  their  outer  cor- 
ners and  turn  somewhat  round  the  edge  of  the  Cricoid,  to  be  attached 
to  the  lower  part  of  its  back ;  their  action  is  to  draw  the  outer  corners 
of  the  Arytenoid  cartilages  outwards  and  downwards,  so  that  the 
points  to  which  the  vocal  ligaments  are  attached  are  separated  from 
one  another,  and  the  rima  glottidis  is  thrown  open.  The  action  of 
these  muscles  is  antagonized  by  that  of  the  Arytenoideus  transversus, 
which  draws  together  the  Arytenoid  cartilages;  and  by  that  of  the 
Crico-arytenoidei  laterales  of  the  two  sides  (n  x),  which  run  forwards 
and  downwards  from  the  outer  corners  of  the  Arytenoid  cartilages,  and 
tend  by  their  contraction  to  bring  together  their  anterior  points,  to 
which  the  Vocal  ligaments  are  attached. — The  depression  of  the  front 
of  the  Thyroid  cartilage,  and  the  consequent  tension  of  the  Vocal  liga- 
ments, is  occasioned  by  the  conjoint  action  of  the  Orico-thyroidei  of 
the  two  sides,  which  occasions  the  Thyroid  and  Cricoid  cartilages  to 
rotate,  the  one  upon  the  other,  at  the  articulation  formed  by  the  infe- 
rior cornua  of  the  former ;  and  this  action  will  be  assisted  by  the 
Sterno-thyroidei,  which  tend  to  depress  the  front  of  the  Thyroid  carti- 
lage, by  pulling  from  a  fixed  point  below.  On  the  other  hand,  the 
elevation  of  the  front  of  the  Thyroid  cartilage,  and  the  relaxation  of 


556  OF  THE  VOICE  AND  SPEECH. 

the  Vocal  ligaments,  are  effected  by  the  contraction  of  the  Thyro-ary- 
tenoidei  of  the  two  sides  (v  hf),  whose  attachments  are  the  same  as 
those  of  the  Vocal  ligaments  themselves ;  and  this  is  aided  by  the  Thyro- 
Jiyoidei^  which  will  tend  to  draw  up  the  front  of  the  Thyroid  cartilage, 
acting  from  a  fixed  point  above. 

976.  The  muscles  which  govern  the  aperture  of  the  glottis, — those 
namely,  which  separate  and  bring  together  the  arytenoid  cartilages, 
and  thus  widen  or  contract  the  space  between  the  posterior  extremities 
of  the  vocal  ligaments, — have  important  functions  in  connexion  with 
the  Respiratory  actions  in  general ;  standing  as  guards,  so  to  speak,  at 
the  entrance  of  the  lungs.  We  can  entirely  close  the  glottis,  through 
their  means,  by  an  effort  of  the  Will,  either  during  inspiration  or  expi- 
ration ;  and  it  is  a  spasmodic  movement  of  this  sort,  which  is  concerned 
in  the  acts  of  Coughing  and  Sneezing,  the  purpose  of  which  is  to  expel, 
by  a  sudden  and  powerful  blast  of  air,  any  irritating  substances, 
whether  solid,  liquid,  or  gaseous,  which  have  found  their  way  into  the 
air-passages.  These  muscles  appear  to  be  under  the  sole  direction  of 
the  inferior  or  recurrent  laryngeal  nerve ;  which  seems  to  possess  ex- 
clusively motor  endowments.  When  this  nerve  is  divided,  on  each  side, 
or  when  the  par  vagum  is  divided  above  its  origin,  the  muscles  of  the 
larynx  (with  the  exception  of  the  crico-thyroid)  are  paralysed ;  and  the 
aperture  of  the  glottis  may  remain  open,  or  may  be  entirely  closed,  ac- 
cording to  the  manner  in  which  its  lips  are  affected  by  the  currents  of 
air  in  ingress  or  egress.  It  is  found  that,  under  such  circumstances, 
tranquil  respiration  may  be  carried  on  ;  but  that  any  violent  ingress  or 
egress  of  air  will  tend  to  drive  the  lips  of  the  glottis  (these  being  in  a 
state  of  complete  relaxation)  into  apposition  with  each  other,  so  as  com- 
pletely to  close  the  aperture.  The  character  of  the  superior  laryngeal 
nerve  appears  to  be  almost  exclusively  afferent ;  no  muscle,  except  the 
crico-thyroid,  being  thrown  into  contraction  when  it  is  irritated ;  whilst, 
on  the  other  hand,  if  it  be  divided,  neither  the  act  of  coughing,  nor  any 
reflex  respiratory  movement  whatever,  can  be  excited,  by  irritating  the 
lining  membrane  of  the  larynx. 

977.  During  the  ordinary  acts  of  inspiration  and  expiration,  the 
Chordae  vocales  appear  to  be  widely  separated  from  each  other,  and  to 
be  in  a  state  of  the  freest  possible  relaxation.  In  order  to  produce  a 
vocal  sound,  they  must  be  made  to  approach  one  another,  and  their 
inner  faces  must  be  brought  into  parallelism  ;  both  of  which  ends  are 
accomplished  by  the  rotation  of  the  Arytenoid  cartilages :  whilst,  at  the 
same  time,  they  must  be  put  into  a  certain  degree  of  tension,  by  the 
depression  of  the  Thyroid  cartilage.  Both  of  these  movements  take 
place  consentaneously,  and  are  mutually  adapted  to  each  other;  the 
vocal  ligaments  being  approximated,  and  the  rima  glottidis  consequently 
narrowed,  at  the  same  time  that  their  tension  is  increased.  There  is  a 
certain  aperture,  which  is  favourable  to  the  production  of  each  tone, 
although  the  pitch  itself  is  governed  by  the  tension  of  the  Vocal  Cords ; 
and  it  is,  perhaps,  to  a  want  of  consent  between  the  two,  that  the  pecu- 
liarly discordant  nature  of  some  voices,  which  appear  incapable  of  pro- 
ducing a  distinct  musical  tone,  is  due. 

978.  It  has  been  fully  proved,  by  the  researches  of  Willis,  Miiller, 


KEGULATION  OF  THE  PITCH  OF  VOCAL  SOUNDS.        657 

and  others,  that  the  action  of  the  Vocal  ligaments,  in  the  production  of 
sound,  bears  no  resemblance  to  that  of  vibrating  strings  ;  and,^that  it  is 
not  comparable  to  that  of  the  mouth-piece  of  the  flute-^i^Q^  of  the  Or- 
gan ;  but  that  it  is,  in  all  essential  particulars,  the  same  with  that  of 
the  reeds  of  the  Hautboy  or  Clarionet,  or  the  tongues  of  the  Accordion 
or  Concertina.  All  the  phenomena  attending  the  production  of  Musical 
tones  are  fully  explicable  on  this  hypothesis ;  except  the  production  of 
falsetto  notes,  which  has  not  yet  been  clearly  accounted  for. — The 
power  which  the  Will  possesses,  of  determining,  with  the  most  perfect 
precision,  the  exact  degree  of  tension  which  these  ligaments  shall  re- 
ceive, is  extremely  remarkable.  Their  average  length  in  the  Male, 
in  the  state  of  repose,  is  estimated  by  MUller  at  about  T3-100ths  of  an 
inch ;  whilst,  in  the  state  of  greatest  tension,  it  is  about  93-lOOths ;  the 
whole  difference,  therefore,  is  not  above  20-lOOths,  or  one-fifth  of  an 
inch.  In  the  female  glottis,  their  average  dimensions  are  about  51- 
lOOths  and  63-lOOths,  respectively ;  so  that  the  difference  is  here  only 
12-lOOths,  or  less  than  one-eighth  of  an  inch.  Now  the  natural  com- 
pass of  the  voice,  in  most  persons  who  have  cultivated  the  vocal  organ, 
may  be  stated  at  about  two  octaves,  or  24  semitones.  Within  each 
semitone,  a  singer  of  ordinary  capability  could  produce  at  least  ten  dis- 
tinct intervals ;  so  that,  for  the  total  number  of  intervals,  240  is  a  very 
moderate  estimate.  There  must,  therefore,  be  at  least  240  different 
states  of  tension  of  the  vocal  cords,  every  one  of  which  can  be  at  once 
determined  by  the  will,  when  a  distinct  conception  exists  of  the  tone  to 
be  produced  (§  905) ;  and,  as  the  whole  variation  in  their  length  is  not 
more  than  one-fifth  of  an  inch,  even  in  Man,  the  variation  required,  to 
pass  from  one  interval  to  another,  will  not  be  more  than  l-1200th  of 
an  inch. — And  yet  this  estimate  is  much  below  that,  which  might  be 
truly  made  from  the  performance  of  a  practised  vocalist.  The  cele- 
brated Madame  Mara  is  said  to  have  been  able  to  sound  50  different 
intervals  between  each  semitone ;  the  compass  of  her  voice  was  at  least 
40  semitones,  so  that  the  total  number  of  intervals  was  2000.  The 
extreme  variation  in  the  length  of  the  vocal  cords,  even  taking  the 
larger  scale  of  the  Male  larynx,  not  being  more  than  one-fifth  of  an 
inch,  it  may  be  said  that  she  was  able  to  determine  the  contractions  of 
her  vocal  muscles  to  the  ten-thousandth  of  an  inch. 

979.  It  is  on  account  of  the  greater  length  of  the  Vocal  cords,  that 
the  pitch  of  the  voice  is  much  lower  in  Man  tjian  in  Woman :  but  this 
difference  does  not  arise  until  the  end  of  the  period  of  childhood, — the 
size  of  the  larynx  being  about  the  same  in  the  Boy  and  Girl,  up  to  the 
age  of  14  or  15  years,  but  then  undergoing  a  rapid  increase  in  the 
former,  whilst  it  remains  nearly  stationary  in  the  latter.  Hence  it  is 
that  Boys,  as  well  as  Girls  and  Women,  sing  treble;  whilst  Men  sing 
tenor,  which  is  about  an  octave  lower  than  the  treble ;  or  bass,  which  is 
several  notes  lower  still.  The  cause  of  the  variation  in  the  timbre  or 
quality  in  different  voices  is  not  certainly  known ;  but  it  appears  to  be 
due,  in  part,  to  differences  in  the  degree  of  flexibility  and  smoothness 
in  the  cartilages  of  the  larynx.  In  women  and  children,  these  carti- 
lages are  usually  soft  and  flexible,  and  the  voice  is  clear  and  smooth ; 
whilst  in  men,  and  in  women  whose  voices  have  a  masculine  roughness, 


558  OF  THE  VOICE  AND  SPEECH. 

the  cartilages  are  harder,  and  are  sometimes  almost  completely  ossified. 
The  loudness  of  the  voice  depemds  in  part  upon  the  force  with  which 
the  air  is  expelled  from  the  lungs ;  but  the  variations  in  this  respect 
which  exist  among  different  individuals,  seem  partly  due  to  the  degree 
in  which  its  resonance  is  increased  by  the  vibration  of  the  other  parts 
of  the  larynx,  and  of  the  neighbouring  cavities.  In  the  Howling 
Monkeys  of  America,  there  are  several  pouches  opening  from  the 
larynx,  which  seem  destined  to  increase  the  volume  of  tone  that  issues 
from  it ; — one  of  these  is  excavated  in  the  substance  of  the  hyoid  bone 
itself.  Although  these  Monkeys  are  of  inconsiderable  size,  yet  their 
voices  are  louder  than  the  roaring  of  lions,  and  are  distinctly  audible  at 
the  distance  of  two  miles ;  and  when  a  number  of  them  are  congregated 
together,  the  effect  is  terrific. 

980.  The  vocal  sounds  produced  by  the  action  of  the  larynx  are  of 
very  different  characters ;  and  may  be  distinguished  into  the  ctt/,  the 
song,  and  the  ordinary  or  acquired  voice.  The  cry  is  generally  a  sharp 
sound,  having  little  modulation  or  accuracy  of  pitch,  and  being  usually 
disagreeable  in  its  timbre  or  quality.  It  is  that  by  which  animals 
express  their  unpleasing  emotions,  especially  pain  or  terror ;  and  the 
Human  infant,  like  many  of  the  lower  animals,  can  utter  no  other 
sound. — In  song,  by  the  regulation  of  the  vocal  cords,  definite  and  sus- 
tained musical  tones  are  produced,  which  can  be  changed  or  modulated 
at  the  will  of  the  individual.  Different  species  of  Birds  have  their 
respective  songs ;  which  are  partly  instinctive,  and  partly  acquired  by 
education.  In  Man,  the  power  of  song  is  entirely  acquired  ;  but  some 
individuals  possess  a  much  greater  facility  in  acquiring  it  than  others, 
— this  superiority  appearing  to  depend  upon  their  more  precise  con- 
ception of  the  tones  to  be  sounded,  as  well  as  their  more  ready  imitation, 
— besides  differences  in  the  construction  of  the  larynx  itself.  The 
larynx  of  an  accomplished  vocalist,  obedient  to  the  expression  of  the 
emotions,  as  well  as  to  the  dictates  of  the  will,  may  be  said  to  be  the 
most  perfect  musical  instrument  ever  constructed. — The  voice  is  a  sound 
more  resembling  the  cry,  in  regard  to  the  absence  of  any  sustained 
musical  tone ;  but  it  differs  from  the  cry,  both  in  the  quality  of  its 
tone,  and  in  the  modulation  of  which  it  is  capable  by  the  will.  In 
ordinary  conversation,  the  voice  passes  through  a  great  variety  of 
musical  tones,  in  the  course  of  a  single  sentence,  or  even  a  single  word, 
sliding  imperceptibly  from  one  to  another ;  and  it  is  when  we  attempt 
to  fix  it  definitely  to  a  certain  pitch,  that  we  change  it  from  the  speak- 
ing to  the  singing  tone. 

981.  The  power  of  producing  articulate  sounds,  from  the  combination 
of  which  Speech  results,  is  altogether  independent  of  the  Larynx ;  being 
due  to  the  action  of  the  muscles  of  the  mauth,  tongue  and  palate. 
Distinctly-articulate  sounds  may  be  produced  without  any  vocal  or 
laryngeal  tone,  as  when  we  whisper;  and  it  has  been  experimentally 
shown,  that  the  only  condition  necessary  for  this  mode  of  speech  is  the 
propulsion  of  a  current  of  air  through  the  mouth,  from  back  to  front. 
On  the  other  hand,  we  may  have  the  most  perfect  laryngeal  tone  without 
any  articulation ;  as  in  the  production  of  musical  sounds,  not  connected 
with  words.     But  in  ordinary  speech,  the  laryngeal  tone  is  modified  by 


ARTICULATE   SPEECH — VOWELS   AND   CONSONANTS.  559 

the  various  organs  which  intervene  between  the  larynx  and  the  os 
externum.  The  simplest  of  these  modifications  is  that  by  which  the 
Vowel  sounds  are  produced, — these  sounds  being  continuous  tones, 
modified  by  the  form  of  the  aperture  through  which  they  pass  out. 
Thus,  let  the  reader  open  his  mouth  to  the  widest  dimensions,  depress 
the  tongue,  and  raise  the  velum  palati,  so  as  to  make  the  exit  of  air  as 
free  as  possible ;  on  then  making  a  vocal  sound,  he  will  find  that  this 
has  the  character  of  the  vowel  a  in  ah.  On  the  other  hand,  if  he  draw 
together  the  lips,  still  keeping  the  tongue  depressed,  he  will  pass  to  the 
sound  represented  in  the  English  language  by  oo,  in  the  Continental 
languages  by  u.  By  attention  to  the  production  of  other  vowel  sounds, 
it  will  be  found  that  they  are  capable  of  being  formed  by  similar  modi- 
fications in  the  form  of  the  buccal  cavity  and  the  size  of  the  buccal 
orifice ;  and  that  they  are  capable  of  being  sustained  for  any  length  of 
time.  There  is  an  exception,  however,  in  regard  to  the  sound  of  the 
English  i,  as  in  fine,  which  is,  in  reality,  a  diphthongal  sound,  produced 
in  the  act  of  transition  from  a  peculiar  indefinite  murmur  to  the  sound 
of  the  long  e,  which  takes  its  place  when  we  attempt  to  continue  it. 
The  short  vowel  sounds,  moreover,  such  as  a  in  fat,  e  in  met,  o  in  pot, 
&c.,  are  not  capable  of  being  perfectly  prolonged,  as  they  require,  for 
their  true  enunciation,  to  be  immediately  followed  by  a  consonant. — A 
tolerably  goocj  artificial  imitation  of  Vowel  sounds  has  been  effected  by 
means  of  a  reed-pipe  representing  the  larynx,  surmounted  by  an  India- 
rubber  ball,  with  an  orifice,  representing  the  cavity  and  orifice  of  the 
mouth.  By  modifying  the  form  of  the  ball,  the  different  vowels  could 
be  sounded  during  the  action  of  the  reed. 

982.  In  the  production  of  the  sounds  termed  Consonants,  the  breath 
suffers  a  more  or  less  complete  interruption,  in  its  passage  through  the 
parts  anterior  to  the  larynx.  The  most  natural  primary  division  of 
these  sounds  is  into  those  which  require  a  total  stoppage  of  the  breath 
at  the  moment  previous  to  their  being  pronounced,  and  which,  there- 
fore, cannot  be  prolonged ;  and  those  in  pronouncing  which  the  inter- 
ruption is  partial,  and  which  can,  like  the  vowel  sounds,  be  prolonged 
ad  libitum.  The  former  have  received  the  designation  of  explosive  con- 
sonants ;  the  latter  are  termed  continuous. — In  pronouncing  any  conso- 
nants of  the  explosive  class,  the  posterior  nares  are  completely  closed ; 
and  the  whole  current  of  air  is  directed  through  the  mouth.  This  may 
be  checked  by  the  approximation  of  the  lips,  a^  in  pronouncing  b  and  p  ; 
by  the  approximation  of  the  point  of  the  tongue  to  the  front  of  the  palate, 
as  in  pronouncing  d  and  t;  or  by  the  approximation  of  the  middle  of 
the  tongue  to  the  arch  of  the  palate,  as  in  pronouncing  the  hard  g  or  h. 
The  difference  between  h,  d,  and^,  on  the  one  hand,  andp,  t,  and  h,  on  the 
other,  depends  simply  upon  the  greater  extent  of  the  meeting  surfaces 
in  the  former  case  than  in  the  latter. — In  sounding  some  of  the  con- 
tinuous consonants,  the  air  is  not  allowed  to  pass  through  the  nose ;  but 
the  interruption  in  the  mouth  is  incomplete ;  this  is  the  case  with  v  and 
/,  s  and  z.  In  others,  the  posterior  nares  are  not  closed,  and  the  air 
has  a  nearly  free  passage,  either  through  the  nose  alone,  as  in  m  and  n, 
or  through  the  nose  and  mouth  conjointly,  as  in  I  and  r.  The  sound  of 
^  is  a  mere  aspiration,  caused  by  an  increased  force  of  breath ;  and  that 


560  OF  THE   VOICE  AND   SPEECH. 

of  the  guttural  ch,  as  it  exists  in  Welsh,  Gaelic,  and  most  Continental 
languages,  is  an  aspiration  modified  by  the  elevation  of  the  tongue, 
which  causes  a  slight  obstruction  to  the  air,  and  an  increased  resonance 
in  the  back  of  the  mouth. 

983.  The  study  of  the  mode  in  which  the  different  Consonants  are 
produced,  is  of  particular  importance  to  those  who  labour  under  defec- 
tive speech,  especially  that  difficulty  which  is  known  as  Stammering. 
This  very  annoying  impediment  is  occasioned  by  a  want  of  proper 
control  over  the  muscles  concerned  in  Articulation ;  which,  instead  of 
obeying  the  Will,  are  sometimes  affected  with  an  involuntary  or  spas- 
modic action,  that  interrupts  the  pronunciation  of  particular  words, — 
just  as,  in  Chorea,  the  muscles  of  the  limbs  are  interrupted  by  spas- 
modic twitchings,  in  the  performance  of  any  voluntary  movement.  In 
fact,  persons  affected  with  general  Chorea  frequently  stammer ;  show- 
ing that  ordinary  Stammering  may  be  considered  as  a  kind  of  local 
Chorea.  The  analogy  between  the  two  states  is  further  indicated  by 
the  corresponding  influence  of  excited  Emotions  in  aggravating  both. 
— It  is  in  the  pronunciation  of  the  consonants  of  the  explosive  class, 
that  the  stammerer  usually  experiences  the  greatest  difficulty ;  for  the 
total  interruption  to  the  breath,  which' they  occasion,  is  frequently  con- 
tinued involuntarily  ;*  so  that  either  the  expiration  is  entirely  checked, 
the  whole  frame  being  frequently  thrown  into  the  most  distressing  semi- 
convulsive  movements,  or  the  sound  comes  out  in  jerks.  Sometimes, 
however,  the  spasmodic  action  occurs  in  the  pronunciation  of  vowels  and 
continuous  consonants  ;  the  stammerer  prolonging  his  expiration,  with- 
out being  able  to  check  it. 

984.  The  best  method  of  curing  this  defect  (where  there  is  no  mal- 
formation of  the  organs  of  speech,  but  merely  a  want  of  power  to  use 
them  aright),  is  to  study  the  particular  difficulty  under  which  the  indi- 
vidual labours ;  and  then  to  cause  him  to  practise  systematically  the 
various  movements  concerned  in  the  production  of  the  sounds  in  ques- 
tion, at  first  separately,  and  afterwards  in  combination, — until  he  feels 
that  his  voluntary  control  over  the  muscles  is  complete.  The  patient 
would  at  first  do  well  to  practise  sentences,  from  which  the  explosive 
consonants  are  omitted ;  his  chief  difficulty,  arising  from  the  spasmodic 
suspension  of  the  expiratory  movement,  being  thus  avoided.  Having 
mastered  these,  he  may  pass  on  to  others,  in  which  the  difficult  letters 
are  sparingly  introduced  ;  and  may  finally  accustom  himself  to  the  use 
of  ordinary  language.  One  of  the  chief  points  to  be  aimed  at,  is  to 
make  the  patient  feel  that  he  has  command  over  his  muscles  of  articu- 
lation ;  and  this  is  best  done,  by  gradually  leading  him  from  that  which 
he  can  do,  to  that  which  he  fears  to  attempt. 

*  The  interruption  of  the  expiratory  movement  in  Stammering,  is  usually  stated  to 
take  place  in  the  glottis  ;  but  the  Author  is  satisfied  that,  in  all  ordinary  cases  at  least, 
it  is  in  that  condition  of  the  mouth,  -which  is  preparatory  to  the  pronunciation  of  one  of 
the  explosive  consonants. 


INDEX. 


N.B.  The  Numbers  refer  to  the  Paragraphs. 


Aberration  corrected  in  eye,  957. 
Absorbent  Cells,  243-245. 

Vessels,  489. 
Absorption,  from  alimentary  canal,  489, 490 ; 
by    lacteals,    243,    244  ;    by 
blood-vessels,  491-493. 
from    general    and    pulmonary* 

surfaces,  522,  523. 
interstitial,  by  lymphatics,  502, 
503;   by  blood-vessels,   502, 
503. 
Adipose  tissue,  257-263,  423-425. 
Age,  influence  of,  on  pulse,  579 ;  on  nutrition, 

622-627. 
Air-cells  of  lungs,  676-679. 
Albumen,  167-171. 

conversion  of,  into  fibrine,  519. 
Albuminous  compounds  of  Plants,  174. 
Albuminuria,  533,  746. 
Algae,  development   and  generation  of,  779, 

780. 
Aliment,  sources  of  demand  for,  406-415. 

effect  of  variations  in  supply  of,  416- 

426. 
relative  value  of  different  kinds  of, 

427-441. 
necessity  for  mixture  in,  437. 
Allantois,  formation  of,  817. 
Amnion,  formation  of,  816. 
Amphioxus,  see  Lancelot. 
Anterior  Pyramids,  890. 
Apoplexy,  688,  924. 
Area  germinativa,  806. 
pellucida,  807. 
vasculosa,  551,  813. 
Areolar  tissue,  194-196,  205. 
Arteries,  movement  of  Blood  in,  582-588. 

elasticity  of,  583;  tonicity  of,  584; 
contractility  of,  585,  586  ;  pulsa- 
tion of,  583,  584  ;  uniform  capacity 
of,  587  ;  anastomosis  of,  588. 
Articulata,  circulation  in,  552,  553  ;  respi- 
ration in,   657-661  ;    nervous    system    in, 
856-863. 
Articulate  speech,  981,  982. 
Asphyxia,  628,  703-709. 
Assimilating  cells,  514,  519. 
Assimilation,  519  ;  by  the  liver,  493. 
Asthma,  678. 
Atrophy,  619,  620. 
Attention,  effects.of,  935. 
Auditory  ganglia,  900. 
nerve,  950. 


Azotized  Compounds  in  Plants,  174,  428, 429. 
in    Animals,    167-179, 

428,  429. 
destination  of,  in  food, 

429,  433. 

Basement  membrane,  206-209. 

Batrachia,  respiration  of,  670,  671. 

Bile,  composition  and  properties  of,  724-726. 

uses  of,  in  digestion,  476-479. 
Birds,  circulation  in,  564,  565;  respiration  in, 
672-674 ;  lymphatic  system  in,  500  ;  nerv- 
ous centres  of,  872 ;  heat  of,  761. 
Blastodermic  vesicle,  805,  806. 
Blastema,  organizable,  213. 
Blood,  composition  of,  525-528;  uses  of  seve- 
ral constituents  of,  529, 530 ;  changes 
of,  in  disease,  531-534. 
corpuscles  of,  white,  214 ;  red,  215-223. 
coagulation  of,  535. 
buffy.coatof,  536,  537. 
rate  of  movement  of,  577. 
influence  of  respiration  on,  699-702. 
Blushing,  603. 

Bone,  structure  and  composition  of,  287-299 ; 
development  of,  300-306  ;  regeneration  of, 
307-309. 
Brunner's  glands,  450,  480. 
Buffy  coat  of  blood,  536,  537. 
Butyric  acid,  430,833. 

Caecum,  secondary  digestion  in,  481. 
Canaliculi  of  Bone,  290. 
Cancelli  of  Bone,  289. 
Cancer-cells,  212,  255. 

Capillaries /movement  of  Blood  in,  589-604; 
variations  in  its  rate,  597. 
variations  in  size  of,  595,  603  ; 
influence  of  nerves  upon,  603, 
604. 
independent  force  generated  in, 
598-600. 
Carbonic  acid,  decomposition   of,  by  Plants, 
79-87  ;  necessity  for  excre- 
tion of,  641  ;  sources  of,  in 
Animal  bodies,  642-648. 
mode  of  its  extrication,  649- 
652  ;  amount  set  free,  691- 
698. 
Cartilage,  264-273;  multiplication  of  cells  of, 

212;  ossification  of,  300-303. 
Caseine,  172,  832. 
Catamenia,  798,  799. 


3G 


►62 


INDEX. 


Cells,  vegetable,  general  history  of,  26-42. 

animal,  general  history  of,  210,  211; 

production  of,  212,  213. 
isolated,  various  forms  of,  214-216. 
the  immediate  agents  in  Organic  func- 
tions, 246,  247. 
union  of,  248-254. 
coalescence  of,  252-254. 
changes  of  form  in,  255. 
Cementum,  319. 

Centipede,  experiments  on,  858,  859. 
Cerebellum,  867-869. 

functions  of,  908-911. 
Cerebric  acid,  383. 
Cerebrum,  867-873. 

functions  of,  912-925. 
Chlorosis,  state  of  blood  in,  219,  532,  537. 
Cholesterine,  724. 
Chondrine,  177. 
Chorda  dorsalis,  211,  251,  812. 
Chordae  vocales,  974-979. 
Chorea,  983. 

Chorion,  795,  809,  817,  818. 
Chyle,  composition  and  properties  of,  515-519. 

corpuscles  of,  214,  518,  519. 
Chyme,  473,  476. 
Cilia,  234,  235. 
£!ineritious  substance,  379. 
Circulation,  538,  539;  in  Plants,  540-548; 
in  lowest  Animals,  549, 550 ;  in  Echi- 
nodermata,  552;  in  Articulata,  552, 
553 ;  in  Mollusca,  555-557 ;  in  Fishes, 
558-560;    in   Reptiles,  561-563;    in 
Birds  and  Mammals,  564,  565. 
in   early   embrvo,  551,  554,   566;    in 
fcEtus  at  birth,  823,  824. 
Coagulation,  of  Albumen,  168,  169;  of  Blood, 
535;  of  Caseine,  172;    of  Chyle,  518;    of 
Fibrine,  180-187. 
Cochlea,  952. 

Cold, degree  of,  sustainable  by  Plants,  1 10, 1 11. 
degree  of,  sustainable  by  Animals,  136. 
Colostrum,  835. 
Colours,  perception  of,  971. 
Commissures  of  brain,  913-916. 
Complementary  colours,  972. 
Co7ichifera,  nervous  system  of,  852,  853. 
Concussion,  581. 
Congestion,  arterial,  601,  602. 
venous,  609,  610. 
Consensual  actions,  903-905. 
Consonants,  982. 
Contractility  of  Muscle,  347. 

of  Vegetable  tissues,  345,  346. 
Convulsive  actions,  885. 
Coral,  277. 
Cornea,  274. 
Corpora  Malpighiana  of  the  Spleen,  506;  of 

the  Kidney,  728. 
Corpora  Quadrigemina,  873,  900,  902. 
Striata,  901. 
Wolffiana,  727. 
Corpus  Callosum,  915. 

Luteum,  800. 
Corpuscles  of  Blood,  red,  215-223 ;  white,  214. 

of  Chyle  and  Lymph,  214. 
Correlation  of  Forces,  53-61. 
Cortical  substance  of  brain,  380. 
Cranium,  circulation  in,  611. 
Crura  cerebri,  894. 
Crustacea,  geographical  distribution  of,  133; 

shells  of,  286  ;  respiration  of,  658. 
Crusta  petrosa,  319. 


Cryptogamia,  generation  of,  780. 

Crystalline  lens,  275. 

Cuttle-fish,  nervous  cords  in  arms  of,  854. 

Daltonism,  971. 

Death,  somatic,  65,  68,  69,  628,  629. 
molecular,  66,  67. 

Decidua,  810,811. 

Decussation,  of  Anterior  Pyramids,  890;  of 
Posterior  Pyramids,  893;  of  Optic  Nerves, 
907. 

Defecation,  462,  463. 

Deglutition,  453,  454,  897. 

Dentine,  311-316. 

Determination  of  blood,  601. 

Development,  early  history  of,  in  Plants,  781 ; 
in  Animals,  784,  785  ;  see  Embryo. 

Developmental  process,  influence  of  heat  on, 
124-127. 

Diff^usion,  mutual,  of  gases,  650. 

Digestion,  organs  of,  442-450. 

nature  of  the  process  of,  471,  472. 

Disintegration  of  tissues,  617;  of  Muscular 
tissue,  361 ;  of  Nervous  tissue,  384. 

Distances,  estimate  of,  966,  967. 

Doris,  gills  of,  651,  656. 

♦Dormant  Vitality,  43-46. 

Double  vision,  963. 

Draper,  Prof.,  his  views  on  the  capillary  cir- 
culation, 545-548,  598,  599. 

Dreaming,  924. 

Duration  of  pregnancy,  825,  826. 

of  impressions  on  Ear,  956. 
of  impressions  on  Eye,  970. 

Dytiscus,  experiments  on,  859. 

Ear,  structure  of,  950-952. 
Echinodermata,  shells  of,  278,  279 ;  circula- 
tion in,  552. 
Electricity,  development  of,  in  Animals,  771- 
777;  in  Torpedo  and  Gymno- 
tus,  771-774  ;  in  Muscles,  775; 
in  the  Frog,  776 ;  in  higher  ani- 
mals, 777. 
influence  of,  on  organized  bodies, 
142;  on  Vegetation,  143,  144; 
effects  of  shocks  of,  145  ;  influ- 
ence of,  on  Animals,  146-148 ; 
on   Muscles,   351 ;    on  nerves, 
396,  932. 
Embryo,  early  development  of,  805,  808  ;  for- 
mation of  vertebral  column  in,  812  ;  forma- 
tion of  vessels  in,  813  ;  formation  of  heart 
in,  814;  formation  of  digestive   cavity  in, 
815  ;  circulation  in,  551,  554,  556. 
Emotional  movements,  917,  919. 
Emotions,  influence  of,  on  hunger,  483  ;   on 
salivary  secretion,  467  ;  on  heart's  action, 
580  ;  on  capillary  circulation,  603  ;  on  mam- 
mary secretion,  836,  837. 
Enamel,  318. 
Endosmose,  491,  492. 
Entozoa,  circulation  in,  549,  550. 
Epidermis,  224-228. 
Epilepsy,  886. 
Epithelium,  231-239. 
Erect  vision,  963. 

Exhalation  of  water,  from  lungs,  701 ;  from 
cutaneous  surface,  743-746. 
of  organic  matter,  702,  746. 
Excreting  processes,  general  review  of,  751- 

759. 
Eye,  structure  of,  956-960. 


INDEX. 


563 


Facial  nerve,  888. 

Fat,  257-263,  423-425. 

Fatty  liver,  754. 

Fecundation  of  ovum,  803,  804. 

Ferments,  action  of,  on  blood,  534. 

Fertilization  of  ovum,  803,  804. 

Fibre,  white,  189,  191. 
yellow,  190,  192. 

Fibres,  formation  of,  from  cells,  193. 

Fibrillation,  183,  213. 

Fihrine,  coagulation  of,  180-187. 
composition  of,  178,  179. 
production  of,  519. 

Fibrous  membranes,  188. 

Fibrous  tissues,  simple,  188-193. 

Fibro- Cartilage,  188,  269,  272. 

Fifth  Pair,  686,  888. 

Fishes,  lymphatic  system  in,  499  ;  circulation 
in,  558-560;  respiration  in,  663-667;  heat 
of,  760;  electricity  of,  771-774;  nervous 
centres  in,  869,  870. 

FcEtus,  circulation  in,  822-824. 

Follicles  of  glands,  238,  714-719. 

Follicles  of  Lieberkiihn,  449. 

Food,  see  Aliment. 

Force,  abstract  nature  of,  18,  71. 

Forces,  Physical,  see  Physical  Forces. 

Vital,  see  Vital  Forces ;  their  relation 
to  the  Physical,  61. 


Gall-bladder,  478. 

Ganglion,  380. 

Gangrene,  634. 

Gases,  mutual  diffusion  of,  650. 

Gastric  fluid,  properties  and  actions  of,  468- 
472. 
conditions  of  its  secretion,  474, 
475. 

Gastric  follicles,  469. 

Gelatinous  nerve-fibres,  375. 

Gelatine,  175,  176,  264,  298;  uses  of,  as  food, 
429. 

Gemmation,  in  Plants,  779;  in  Animals,  782. 

Generation,  essential  character  of  the  pro- 
cess, 780-783  ;  action  of  the  male  in,  786- 
790  ;  action  of  the  female  in,  791-804. 

Geographical  distribution  of  Animals,  133. 

distribution  of  Plants,  102-106. 

Germ-cells,  240,  242,  780,  783. 

Germinal  membrane,  805.  | 

spot,  794.  1 

vesicle,  794.  | 

Gestation,  duration  of,  825,  826.  I 

Gills,  structure  of,  651,  655,  656,  663. 

Glands,  essential  parts  of,  238,  714-719. 

Globuline,  221. 

Glosso-pharyngeal  nerve,  888,  897. 

Glottis,  regulation  of  aperture  of,  976. 

Glycerine,  260. 

Glycocoll,  176,  734. 

Gout,  422,  615. 

Graafian  Vesicle,  796. 

Granulation,  637. 

Gravity,  influence  of,  on  venous  circulation, 
609,  610. 

Gray  nerve-fibres,  375. 

Gymnotus,  771-774. 

222. 


Hsematine,  221, 
Hair,  328-330. 
Haversian  canals,  293-297. 
Hearing,  sense  of,  949-954. 


Heart,  action  of,  568-570;  sounds  of,  571- 
575  ;  propulsive  power  of,  576-578 ; 
frequency  of  contractions  of,  579. 
power    of,    independent    of  nervous 
agency,  580  ;  influenced  by  mental 
emotions,  580;  by  state  of  nervous 
system,  581. 
first  development  of,  in  embryo,  554, 
566,  814. 
Heat,  amount  of,  developed  in  Insects,  123; 
in  Fishes,   760 ;   in   Birds,   761;   in 
Mammals,  761 ;  in  Plants,  762. 
development  of,  chiefly  dependent  on 
production  of  carbonic  acid,  763,  764  ; 
but  partly  on  other  oxidizing  pro- 
cesses, 765 ;    inferior  in  young  ani- 
mals, 766. 
of  body,  kept  down  by  perspiration, 

745,  768. 
its  influence  upon  vital  activity  in  gene- 
ral, 97,  98;  upon  Vegetation,  99-111 ; 
upon  Animal  life,  112-141. 
degree  of,  sustainable  by  Animals,  138- 
141  ;  by  Plants,  108. 
Hemispheres,  Cerebral,  912-916. 
Hippuric  acid,  730,  734. 
Hunger,  sense  of,  483-485. 
Hybernation,  120,  121. 
Hydra,  stomach  of,  443. 
Hydrophobia,  886,  908. 
Hypertrophy,  617,  618. 
Hypo-glossal  nerve,  888. 
Hysteria,  741,  887,  908. 

Inanition,  Chossat's  experiments  on,  117. 

Incubation,  heat  supplied  in,  125-127. 

Inflammation,  nature  of  the  process,  631 ,  632 ; 
state  of  the  blood  in,  531,  536. 

Inorganic  substances  in  food,  438-441. 

Insalivation,  446,  451,  452. 

Insects,  circulation  in,  552;  respiration  in, 
659,  660 ;  nervous  system  of,  856-864  ;  re- 
flex actions  of,  858-860;  instinctive  actions 
of,  860,  861 ;  heat  of,  123. 

Instinctive  actions  of  Man,  904. 

Intelligence,  913,  920. 

Intercellular  substance,  248-253. 

Intestinal  canal,  structure  of,  447-450;  move- 
ments of,  460,  461. 

Iris,  movements  of,  969. 

Irritability  of  Muscles,  348-363. 

Kidneys,  structure  of,  727,   728;   action  of, 

729-741,  755. 
Kreatine,  735. 
Kreatinine,  73^5. 

Lacteals,  494,  496,  499. 

Lactic  acid,  in  gastric  fluid,  470;  in  urine,  735. 

Lacunae  of  Bone,  290. 

Laminae  dorsales,  812. 

Lancelot,  215,  251,  560,  869. 

Laryngeal  nerves,  976. 

Larynx,  structure  and  actions  of,  974,  979. 

Lead-palsy,  614. 

Leucin,  170,  176. 

Light,  laws  of  transmission  and  refraction  of, 

955. 
influence  of,  on  vegetation,  79-92 ;  on 

growth  and  development  of  animals, 

93-96. 
emission  of,  by  animals,  769 ;  by  man, 

770. 


5G4 


INDEX. 


Life,  idea  of,  49 ;  conditions  of,  70 ;  duration 

of,  25. 
Lime,  in  Animal  body,  43S,  440,  44L 
Lithic  acid,  732,  733. 

diathesis,  422,  733. 
Liver,    structure    of,    720-723;    assimilating 

action  of,  493;  secreting  action  of,  476-479, 

724-726. 
Luminousness,  animal,  769,  770. 
Lungs,  structure  of,  676-679. 
Lymph,  composition  and  properties  of,  515,520. 
Lymphatics,  498-503. 

Male,  action  of,  in  reproduction,  786-790. 

Malignant  diseases,  640. 

Malpighian  bodies,  of  Kidney,  728;  of  Spleen, 

506. 
Mammalia,  lymphatic  system  in,  500;  cir- 
culation in,  564,  565;  respiration  in,  674- 
676 ;  heat  evolved  in,  761 ;  nervous  centres 
of,  873  ;  ovisac  of,  795. 
Mammary  glands,  830,  831. 
Margarine,  259. 

Mastication,  act  of,  451,  452,  896. 
Medulla    Oblongata,   structure  of,  889-893; 

functions  of,  894-899. 
Memory,  924. 

Menstrual  secretion,  798,  799. 
Mesenteric  glands,  496. 
Metamorphosis  of  animals,  407,  784,  785';  in- 
fluence of  heat  upon,  127. 
Milk,  436 ;    composition  and  properties  of, 
832-834. 
circumstances  influencing  secretion  of, 
836-839. 
Mineral  ingredients  of  food,  438-441. 
Moisture,  proportion  of,  in  diflferent  parts  of 
the  body,  149-152;  necessity  of,  for  growth 
of  Plants  and  Animals,  153-157 ;   effects 
of  withdrawal  of,  158-161. 
MoLLUscA,  circulating  system  of,  555-557 ; 
respiratory  organs    of,    654-656 ;    nervous 
system  of,  850-854. 
Mucous  membrane,  199-204. 
Mucus,  237,  464. 
Mulberry  mass,  784,  805. 
Muscles,    contractility    of,    345-371 ;    irrita- 
bility  of,   348-363;    tonicity  of, 
364-366;     rigor    mortis    of,  367 
-369 ;    peculiar    force    of,    370 ; 
heat  evolved  by,  371 ;   electricity 
evolved  by,  775. 
energy  of,  dependent  on  supply  of 

blood,  358-360. 
disintegration  of,  361. 
Muscular    fibre,    striated,    332-336;     non- 
striated,  337;    development  of,  338,   339; 
vessels  and  nerves  of,  340,  341. 
Muscular  sense,  904. 
Myolemma,  333. 
Myopia,  958. 

Nail,  226. 

Nervous  System,  general  view  of  actions  of, 
840-848. 

Nervous  System,  in  Radiata,  849;  in  Tuni- 
cata,  850,  851  ;  in  Bivalve  Mollusca,  852, 
853 ;  m  higher  Mollusca,  854 ;  in  Articu- 
lata,  855-863  ;  in  Vertebrata,  867,  868  ;  in 
Fishes,  869,  870;  in  Reptiles,  871;  in 
Birds,  872;  in  Mammals,  873. 

Nervous  tissue,  372-405  ;  fibrous,  373-377  ; 
vesicular,  378,  379;    arrangement  of  ele- 


ments of,  in  nervous  centres,  380  ;  in  peri- 
phery, 381,  382;  chemical  composition  of, 
383  ;    disintegration  and  renewal  of,   384- 
389  ;  conditions  of  activity  of,  390-404. 
Neurilemma,  373. 
Nucleus,  211. 
Nutrition,  612-615. 

activity  of,  dependent  on  func- 
tional activity  of  parts,  616-627. 

(Esophagus,  passage  of  food  along,  455,  898. 

Oily  compounds  in  food,  430,  432,  435 ;  im- 
portance of,  530. 

Oleine,  259. 

Oleo-phosphoric  acid,  383. 

Olfactive  lobes,  869-873,  900. 

Olfactory  nerve,  906,  946,  947. 

Olivary  bodies,  891. 

Omphalo-mesenteric  vessels,  813. 

Optic  lobes,  869-873,  900. 

Optic  nerves,  906,  907,  960. 

Orbit,  motor  nerves  of  the,  888. 

Organized  structures,  general  characters  of, 
2-15. 

Osseous  tissue,  see  Bone. 

Ossification,  300-303. 

Otolithes,  950. 

Ova  of  animals,  791-795. 

Ovarium,  793-797. 

Ovisac,  792,  796. 

Oxygen,  necessity  for,  in  animal  body,  649  ; 
mode  of  introduction  of,  650-652. 

Pancreatic  secretion,  480. 

Papillse,  sensory,  of  skin,  382, 940;  of  tongue, 

943. 
Parturition,  827-829. 
Par  Vagum,  459,  487,580,  685,  686,  888,  895, 

897-899. 
Pedal  ganglia  in  Mollusca,  852,  853. 
in  Articulata,  857,  862. 
Pepsine,  470,  471. 
Perception,  nature  of,  936,  937. 
Perceptions,  tactual,  941 ;  visual,  961-968. 
Peristaltic  movement,  352,  460. 
Perspiration,  743-746. 
Peyer's  glands,  450,  749. 
Phosphate  of  lime,  in  food,  438-441 ;  in  bone, 

298. 
Phosphatic  deposits,  386,  738-740. 
Phosphorus,  in  animal  body,  438,  439. 
Phanerogamia,  generation  and  development 

of,  780,  781. 
Physical  Forces,  19-23,  52;   correlation  of, 

53-55 ;  relations  of,  to  Vital,  61-63 ;  their 

influence  on  vital  action,  73-78. 
Pigment-cells,  229,  230. 
Placenta,  structure  of,  818-820. 
Placental  tufts,  245,  818. 
Plants,  heat  of,  762;  circulation  in,  540-548; 

respiration  in,  84,  641,  642;  reproduction 

in,  778-781. 
Pneumogastric  nerve,  see  Par  Vagum. 
Polypes,  digestive  process  in,  443,  444. 
Posterior  Pyramids,  893. 
Pregnancy,  duration  of,  825,  826. 
Prehension  of  food,  896. 
Presbyopia,  958. 
Primary  membrane,  206-209. 
Primitive  trace,  812. 
Proteine,  171. 

Puberty  in  male,  788  ;  in  female,  798. 
Pulpofhair,  328,  330. 


INDEX. 


sr) 


Pulpofteeih,  310,  313,  314. 

Pulsations  of  heart,  579. 

Pulse,  in  arteries,  583,  584  ;  respiratory,  in 

veins,  607. 
Pupil,  changes  in  diameter  of,  969. 
Purpurine,  736. 
Pus,  632-637. 
Pyramids,  anterior,  890. 
posterior,  893. 

Radiata,  Nervous  system  of,  849. 

Receptaculum  Chyli,  497. 

Red  corpuscles  of  blood,  characters  of,  215, 

216;  development  of  217-220. 
Reduction  of  food,  provisions  for,  445. 
Eejlex  actions,  nature  of,  392-396. 

of   Articulata,    858-860;    of 
Mollusca,  850,    851,   854;    of 
Vertebrata,  875-879,  884. 
Regeneration  of  parts,  influence  of  heat  upon, 

129;  of  nerve,  389. 
Reproductive  cells,  240-242. 
Reptiles,  circulation  in,  562,  563  ;  lymphatic 
system   in,  499 ;   respiration   in,  668-671 ; 
nervous  centres  in,  871. 
Respiration,  nature  of  the  process,  641 ; 
sources  of   demand  for    it, 
642-648 ;    mode  of  its  per- 
formance, 649-652. 
organs  of,  in  lovv^est  animals, 
653;  in  Mollusca,  654-656; 
in  Annelida,  657;  in  Crus- 
tacea, 658  ;   in  insects,  659, 
660 ;    in    Spiders,   661  ;    in 
Fishes,   663-667;    in    Rep- 
tiles,  668-671  ;    in    Birds, 
672-674;  in  Mammalia  and 
Man,  675-678. 
movements  of,  679-688. 
chemical  phenomena  of,  689- 

702. 
insufficient,  effects    of,    703- 
709. 
Respiratory  nerves,  in  Insects,  862;  in  Mol- 
luscs,   850-853;    in    Vertebrata,   684-688, 
895. 
Respiratory  pulse,  607. 
Restiform  bodies,  892. 
Retina,  general  structure  of,  960. 
Rigor  Mortis,  367-369. 
Ruminating  stomach,  457. 


Saccharine  compounds  in  food,  430-434,  493. 
Salivary  glands,  465. 

secretion,  446,  466,  467. 
Satiety,  sense  of,  486. 
Sebaceous  follicles,  747,  748. 
Secreting  cells,  238,  239,  712-714. 
Secretion,  nature  of  the  process,  710-713. 

eflfects  of  suppression  of,  711. 
Segmentation  of  vitellus,  805. 
Selecting  power  of  individual  parts,  612-615. 
Semicircular  canals,  952. 
Sensation,  389,  390,  930.  931 ;  nerves  of,  389, 

390,  900,  901  ;  general  and  special,  932. 
Sensations,  regulation  of  muscular  movement 

by,  902-904. 
Sensorium,  390. 
Sensory  Ganglia,  900,  901 ;  functions  of,  902 

-905. 
Sensory  nerves,  906,  907. 
Serous  membranes,  197,  198. 


Shell,  of  Echinodermata,  278,  279 ;  of  Mol- 
lusca, 280-285;  of  Articulata,  284-286. 

Sight,  sense  of,  955-972. 

Single  vision  with  two  eyes,  963. 

Size  of  objects,  estimate  of,  968. 

Skin,  199,  205,  742-748,  940. 

Sleep,  924. 

Smell,  sense  of,  946-948. 

Sneezing,  948. 

Solen,  nervous  system  of,  852,  853. 

Somnambulism,  924. 

Sounds,  propagation  of,  949 ;  qualities  of,  954. 

Sounds  of  heart,  571-575. 

Speech,  981,  982. 

Sperm-cells,  240,  241,  780,  783. 

Spermatic  fluid,  786,  787  ;  emission  of,  790. 

Spermatozoa,  240,  786,  787 ;  use  of,  in  fecun- 
dation, 803,  804. 

Sphinx  ligustri,  nervous  system  of,  856,  857. 

Spiders,  respiratory  organs  of,  661. 

Spinal  Cord,  867,  868 ;  its  independence  of 
the  Brain,  874-879;  structure  of,  8S0- 
883 ;  reflex  actions  of,  884  ;  disordered  states 
of,  885-887. 

Spinal  accessory  nerve,  580,  888, 

Spinal  nerves,  origin  of,  880,  882. 
peculiar,  888. 

Spiracles  of  Insects,  659. 

Spleen,  structure  of,  506 ;  uses  of,  507-509. 

Stammering,  983,  984. 

Starchy  compounds  in  food,  430-434. 

Star-fish,  nervous  system  of,  849. 

Starvation,  Chossat's  experiments  on,  117. 

Stearine,  259. 

Stereoscope,  964,  965. 

Stomach,  447,  448 ;  movements  of,  458,  459. 
in  Ruminants,  457. 

Stomato-gastric  nerves  of  Invertebrata,  863. 
of  Vertebrata,  896. 

Strabismus,  963. 

Suction,  act  of,  896. 

Sudoriparous  glandulae,  743,  744. 

Supra-renal  capsules,  510. 

Sympathetic  System,  in   Man,  functions  of, 
926-929. 
traces  of,  among  Invertebrata, 
864. 

Syncope,  581,  628. 

Synovial  membranes,  197,  198. 

Tadpole,  respiration  of,  670;  metamorphosis 

of,  670. 
Taste,  nerves  of,  944. 
sense  of,  945. 
Teeth,  structure    and  development   of,  310- 

327.        "^ 
Temperature,  sense  of,  933,  942. 
Testis,  structure  of,  786. 
Tetanus,  886. 
Thalami  Optici,  901. 
Thirst,  488. 
Thoracic  duct,  497. 
Thymus  Gland,  511,  512. 
Thyroid  Gland,  513. 
Tickling,  907. 
Tongue,  papilla;  of,  943. 
Tonicity  of  arteries,  365,  584;  of  muscle,  364 

-366. 
Torpedo,  electricity  of,  771-774. 
Torpidity,  induced  by  cold,  97,  98,  136;  by 

want  of  moisture,  158-161. 
Touch,  sense  of,  939-942. 
Tubercula  quadrigemina,  869,  870-873,  900. 


566 


INDEX. 


Tubercular  diathesis,  626,  638,  639. 
TuTiicata,  nervous  system  of,  850,  851. 
Tympanum,  951. 
Tyrosin,  170. 

Ulceration,  633. 

Umbilical  vessels,  818. 

Umbilical  vesicle,  815. 

Urea,  730,  731. 

Uric  acid,  732,  733. 

Urine,  composition  and  properties  of,  729- 
740;  effects  of  suppression  of,  741, 

Uterus,  comparative  structure  of,  793 ;  partu- 
rient action  of,  827. 

Vascular  area,  551,  813,  814. 

Vegetable  kingdom,  office  of,  15. 

Vegetation,  influence  of  Light  upon,  79-92; 
influence  of  Heat  upon,  98-107;  influence 
of  Electricity  upon,  143-145. 

Veins,  movement  of  blood  in,  60-5610  ;  pul- 
sation in,  607,  608. 

Venous  congestion,  609,  610. 


Villi  of  mucous  membrane,  243,  492 ;  of  yolk- 
bag,  244  ;  of  placenta,  245. 

Vital  Actions,  16-18,47-51. 

Vital  Forces,  17,  24,  52;  their  relations  to 
each  other,  58-60 ;  to  the  Physical  forces, 
61-63. 

Vital  Stimuli,  61. 

Vitellus,  784,  794;  segmentation  of,  805. 

Vitreous  body  of  eye,  276. 

Vocal  ligaments,  974-979. 

Voice,  production  of,  973-979. 

Voluntary  movements,  nature  of,  923. 

Vowel  sounds,  production  of,  981. 

White  fibrous  tissue,  189,  191. 
Worm  tribes,  circulation  in,  552;  respiration 
in,  657. 

Yellow  fibrous  tissue,  190,  192. 
Yolk,  see  Vitellus. 

Zona  pellucida,  795. 
Zoospores  of  Algs,  779. 


CARPENTER'S    HUMAN    PHYSIOLOGY. 


BLANCHAED  AND  LEA, 

PHILADELPHIA, 

HAVE  JUST  ISSUED 

PRINCIPLES  OF  HUMAN  PHYSIOLOGY, 

WITH  THEIR  CHIEF  APPLICATIONS  TO 

PATHOLOGY.  HYGIENE.  AND  FORENSIC  MEDICINE. 
BY  WILLIAM  B.  CARPENTER,  M.D.,  F.R.S.,  ETC. 

A   NEW   EDITION,    WITH   EXTENSIVE   ADDITIONS    AND   IMPROVEMENTS    BY   THE   AUTHOR. 

Beautifully  Illustrated  with  Lithograpliic  Plates,  and  over  ^00  Wood-cuts. 

IN  ONE  LARGE  AND  HANDSOMELY-PRINTED  OCTAVO  VOLUME. 

In  preparing  a  new  edition  of  this  Tery  popular  text-book,  the  publishers  have  had  it  completely  revised 
by  the  author,  who,  without  materially  increasing  its  bulk,  has  embodied  in  it  all  the  recent  investigations 
and  discoveries  in  physiological  science,  and  has  rendered  it  in  every  respect  on  a  level  with  the  improve- 
ments of  the  day.  Although  the  number  of  the  wood-engravings  has  been  but  little  increased,  a  considera- 
ble change  will  be  found,  many  new  and  interesting  illustrations  having  been  introduced  in  place  of  others 
which  were  considered  of  minor  importance,  or  which  the  advance  of  science  had  shown  to  be  imperfect, 
while  the  plates  have  been  altered  and  redrawn  under  the  supervision  of  the  author  by  a  competent  London 
artist.  In  passing  the  volume  through  the  press  in  this  country,  the  services  of  a  professional  gentleman 
have  been  secured,  in  order  to  insure  the  accuracy  so  necessary  to  a  scientific  work.  Notwithstanding 
these  improvements,  the  price  of  the  volume  is  maintained  at  its  former  moderate  rate. 

In  recommending  this  work  to  their  classes.  Professors  of  Physiology  can  rely  on  their  being  always  able 
to  procure  editions  brought  thoroughly  up  with  the  advance  of  science. 

The  very  rapid  sale  of  a  large  impression  of  the  first  edition  is  an  evidence  of  the  merits  of  this  valuable 
work,  and  that  it  has  been  duly  appreciated  by  the  profession  of  this  country.  The  publishers  hope  that 
the  present  edition  will  be  found  still  more  worth}^  of  approbation,  not  only  from  the  additions  of  the 
author  and  editor,  but  also  from  its  superior  execution,  and  the  abundance  of  its  illustrations. 


"  We  have  much  satisfaction  in  declaring  our  opinion  that  this  work  is  the  best  systematic  treatise  on 
physiology  in  our  own  language,  and  the  best  adapted  for  the  student  existing  in  any  language." — Mcdico- 
Chirurgical  Review. 

''  This  work  as  it  now  stands  is  the  only  Treatise  on  Physiology  in  the  English  language,  which  exhibits 
a  clear  and  connected,  and  comprehensive  view  of  the  present  condition  of  that  science. 

"  Jj'ew  individuals  could  have  been  found  so  well  qualified  as  Dr.  Carpenter  for  acting  as  the  historian  of 
physiological  science.  He  is  endowed  with  great  perseverance  and  industry,  possesses  a  clear  and  logical 
judgment,  is  able  to  see  distinctly  the  salient  points  of  the  more  abstruse  and  disputed  doctrines,  has 
excellent  powers  of  generalization,  and  can  express  his  thoughts  in  lucid  and  correct  language.  In  explain- 
ing the  general  doctrines  of  the  science,  or  in  describing  the  phenomena  attending  the  performance  of 
individual  functions,  he  lays  before  the  reader  a  judicious  admixture  of  the  most  trustworthy  facts,  with 
the  inductions  to  which  they  lead,  which  cannot  fail  to  give  him  a  clear  conception  of  each  subject  brought 
under  his  notice.  When  he  ventures  upon  any  new  generalizations,  he  never  indulges  in  dogmatical  and 
bold  assertions,  but  proceeds  in  a  cautious  and  philosophical  spirit ;  this  cannot  fail  to  exercise  a  salutary 
influence  upon  the  mind  of  the  student  by  repressing  that  tendency  to  hypothetical  speculation  to  which 
young  and  ardent  minds  are  so  prone.  He  omits  no  opportunity  of  pointing  out  how  the  physiological  facts 
and  doctrines  he  is  discussing  may  be  employed  in  furnishing  more  scientific  methods  of  treating  disease." 
— The  London  and  Edinburgh  Monthly  Journal  of  Medical  Sciences. 

"This  work  exhibits  all  the  mental  characteristics  of  Dr.  Carpenter;  great  knowledge  of  what  has  been 
done  by  others,  clearness  of  conception,  and  lucidness  of  arrangement.  Although  entitled  '  Human  Phy- 
siology,' many  of  its  details  are  on  Histology  and  Histogeny,  or  the  minute  anatomy  and  development  of 
tissues  which  man  possesses  in  common  with  the  rest  of  the  animated  creation.  They,  however,  who  are 
fond  of  such  investigations,  and  who  is  there  who  is  not  more  or  less  so,  will  find  the  transcendental  as  well 
as  the  more  sober  views  of  modern  inquiries  well  depicted." — American  Medical  Library. 

"  Though  the  resources  of  the  author's  comprehensive  mind  are  apparently  devoted  to  the  advancement 
of  new  beginners  in  study,  there  is  a  splendid  exhibition  of  the  powers  of  analysis,  an  uncommon  degree  of 
success  in  making  abstruse  objects  clear,  and  in  forcibly  impressing  upon  others  the  laws  of  life  which  he 
so  well  understands,  which  will  give  eclat  to  Dr.  Carpenter's  reputation  when  he  will  be  insensible  to  • 
praise.  All  who  can  afford  to  have  a  good  system  of  physiology  should  possess  this;  and  those  who  are 
able  to  keep  pace  with  the  progress  of  science  should  not  be  without  it.  No  necessity  seems  to  exist  for 
extracting  from  its  pages,  or  commenting  especially  on  any  particular  parts  or  portions  of  the  volume, 
because  it  is  presumed  that  all  who  can  will  avail  themselves  of  it.  Probably  this  improved  edition  does 
not  cost  more  than  one-third  the  price  asked  for  it  in  England,  and  yet  it  is  superior  in  very  many  respects." 
— Boston  Med.  and  Surg.  Journal. 

"  It  would  be  a  dereliction  of  our  biographical  duty  not  specially  to  mention  the  highly-meritorious  work 
of  Dr.  Carpenter  on  the  Principles  of  Human  Physiology,  a  work  to  which  there  has  been  none  published  of 
equal  value  in  the  department  of  which  it  treats,  embodying,  as  it  does,  an  immense  store  of  facts  and 
modern  discoveries  in  anatomy  and  physiology  down  to  the  present  time." — Dr.  Black's  Retrospective 
Address. 

'•  It  is  a  clear  compendious  resume  of  the  existing  state  of  Physiological  Science,  conceived  and  executed 
in  a  genuine  philosophical  spirit,  and  peculiarly  adapted  to  the  medical  student.  All  the  received  facts 
of  physiology  are  presented  in  a  well-digested  form  and  lucid  manner,  and  the  deductions  made  from  them 
show  close  reasoning,  and  a  very  impartial  spirit.  The  author,  though  still  a  young  man,  has  already  won 
a  high  reputation  in  this  department  of  medicine.  In  a  literary  point  of  view,  the  present  work,  as  well  as 
his  other  productions,  are  of  a  high  order;  his  .«tyle  is  clear,  precisse,  and  unostentatious,  at  times  rising  to 
positive  elegance," — Med.  Examiner. 


CARPENTER'S    COMPARATIVE    PHYSIOLOGY 


BLANCHARD   &  LEA, 

PHILADELPHIA, 

HAVE  JUST  ISSUED 

PRINCIPLES  OF  PHYSIOLOGY, 

GENERAL  AND  COMPARATIVE. 
BY  WILLIAM  B.  CARPENTER,  M.D.,  F.R.S.,  ETC. 

THIRD  EDITION,  GREATLY  ENLARGED. 

IN  ONE  VERY  HANDSOME  OCTAVO  VOLUME,  OP  OVER  1100  PAGES,  WITH  321  BEAUTIFUL  WOOD-CUTS. 

This  great  work  will  supply  a  want  long  felt  by  the  scientific  public  of 
the  country,  who  have  had  no  accessible  treatise  to  refer  to,  presenting,  in  an 
intelligible  form,  a  complete  and  thorough  outline  of  this  important  subject. 
The  high  reputation  of  the  author,  on  both  sides  of  the  Atlantic,  is  a  sufficient 
guarantee  for  the  completeness  and  accuracy  of  any  work  to  which  his  name 
is  prefixed;  but  this  volume  comes  with  the  additional  recommendation  that  it 
is  the  one  on  which  the  author  has  bestowed  the  greatest  care,  and  on  which 
he  is  desirous  to  rest  his  reputation.  Two  years  have  been  devoted  to  the  pre- 
paration of  this  edition,  which  has  been  thoroughly  remoulded  and  rewritten, 
so  as,  in  fact,  to  constitute  a  new  work.  The  amount  of  alterations  and  addi- 
tions may  be  understood  from  the  fact  that  of  the  ten  hundred  and  eighty  pages 
of  the  text,  but  one  hundred  and  fifty  belong  to  the  previous  edition.  Con- 
taining, as  it  does,  the  results  of  years  devoted  to  study  and  observation,  it 
may  be  regarded  as  a  complete  exposition  of  the  most  advanced  state  of 
knowledge  in  this  rapidly -progressive  branch  of  science,  and  as  a  storehouse 
of  facts  and  principles  in  all  departments  of  Physiology,  such  as  perhaps  no 
man  but  its  author  could  have  accumulated  and  classified. 

In  every  point  of  mechanical  execution,  and  profuseness  and  beauty  of  illus- 
tration, the  Publishers  risk  nothing  in  saying  that  it  will  be  found  all  that  the 
most  fastidious  taste  could  desire. 

"  A  truly  magnificent  work.    In  itself  a  perfect  physiological  study." — EanJdng^s  Abstract,  July  21,  1851. 

"  It  is  impracticHble  for  us  to  give  an  analysis  of  the  varied  contents  of  this  most  useful  volume.  Its  pro- 
duction has  been  a  labour  of  love  with  its  author,  and  has  subjected  him  to  much  thought,  and  to  no  litt  e 
toil,  without  the  expectation  of  pecuniary  profit.  It  is  to  be  hoped,  however,  that  so  much  ability,  zea), 
and  industry,  may  meet  with  their  reward,  and  that  future  editions  may  remunerate  him  for  productive 
exertions  so  beneficial  in  their  results  to  others.  We  may  remark,  in  conclusion,  that  the  work  is  beautifully 
gotten  up  in  the  English  fashion,  and  that  the  illustrations  are  in  the  first  style  of  art." — Medical  Examiner. 

"  This  work  stands  without  its  fellow.  It  is  one  few  men  in  Europe  could  have  undertaken;  it  is  one  no 
man,  we  believe,  could  have  brought  to  so  successful  an  issue  as  Dr.  Carpenter.  It  required  for  its  produc- 
tion a  physiologist  at  once  deeply  read  in  the  labours  of  others,  capable  of  taking  a  general,  critical,  and 
unprejudiced  view  of  those  labours,  and  of  combining  the  varied,  heterogeneous  materials  at  his  disposal,  so 
as  to  form  an  harmonious  whole. 

"We  feel  that  this  abstract  can  give  the  reader  but  a  very  imperfect  idea  of  the  fulness  of  this  work,  and 
no  idea  of  its  unity,  of  the  admirable  manner  in  which  material  has  been  brought,  from  the  most  various 
sources,  to  conduce  to  its  completeness,  of  the  lucidity  of  the  reasoning  it  contains,  or  of  the  clearness  of 
language  in  which  the  whole  is  clothed.  Not  the  profession  only,  but  the  scientific  world  at  large,  must 
feel  deeply  indebted  to  Dr.  Carpenter  for  this  great  work.  It  must,  indeed,  add  largely  even  to  his  high 
reputation." — Medical  Times. 

" This  is  a  book  without  a  rival;  and  Dr.  Carpenter  has  laid  the  medical  profession,  as  well  as  all  who 
study  and  who  love  natural  history,  under  deep  and  lastiug  obligations  by  its  production.  Our  limits 
forbid  us  from  indulging  in  comment  or  criticism;  and  we  can  only  heartily  commend  the  work  to  our 
readers." — London  Journal  of  Medicine, 

"The  present  edition  contains  upwards  of  one  thousand  pages,  in  close  type,  and  includes  a  mass  of  infor- 
mation not  to  be  easily  found,  even  in  a  well-furnished  library.  Physiology,  Zoology,  Botany,  and  Micro- 
scopy, all  lend  their  aid  to  the  elucidation  of  the  laws  of  life  and  development;  and  the  style  is  such  as  to 
interest  the  reader,  and  to  fix  his  attention  upon  the  particular  subject  to  which  he  has  occasion  to  refer. 
We  must  also  observe  that  the  beautiful  and  accurate  illustrations  which  accompany  this  edition  (exceed- 
ing three  hundred  in  number)  make  plain  to  the  eye  that  in  which  description  would  fail,  and  materially 
aid  the  author  in  familiarizing  his  readers  with  the  results  of  numerous  microscopical  observations. 

'•  It  is  our  opinion  that  whether  for  reference  or  study  in  the  subject  to  which  it  specially  refers,  no  better 
book  than  Dr.  Carpenter's  'Principles  of  Physiology,  (ieneral  and  Comparative,'  can  be  placed  in  the  hands 
of  student  or  practitioner.  It  would  also  be  a  valuable  addition  to  the  library  of  every  well  educated  man, 
although  not  a  member  of  the  profession." — London  Medical  Gazette. 

"  I  recommend  to  your  perusal  a  work  recently  published  by  Dr.  Carpenter.  It  has  this  advantage,  it  is 
very  much  up  to  the  present  state  of  knowledge  on  the  subject.  It  is  written  in  a  clear  style,  and  is  well 
illustrated." — Professor  S'lar/  ey's  Introductory  Lecture. 

"In  Dr.  Carpenter's  work  will  be  found  the  best  exposition  we  possess  of  all  that  is  furnished  by  compa- 
rative anatomy  to  our  knowledge  of  the  nervous  system,  as  well  as  to  the  more  general  principles  of  life  and 
organization." — Dr.  JTcUund's  Medical  Notes  and  Reflections. 

"See  Dr.  Carpenter's  '  Principles  of  General  and  Comparative  Physiology.' — a  work  which  makes  me  proud 
to  think  he  was  once  my  pupil."— Z>r.  EUiotson's  Physiology. 


CATALOGUE 

OP 

BLANCHAllD  &  LEA^S 
MEDICAL  Am  SURGICAL  PUBLICATION'S. 

PHILADELPHIA,  AUGUST,  1853. 


TO   THE    MEDICAL   PROFESSION. 

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Parts  I.,  il.,  and  III.,  with  numerous  wood-cuts. 

WEST'S  LECTURES  ON  THE  DISEASES  OF  INFANCY  AND  CHILDHOOD. 

MALGAIGNE'S  OPERATIVE  SURGERY,  with  wood-cuts,  and 

SIMON'S  LECTURES  ON  GENERAL  PATHOLOGY. 

While  the  year  1853,  presents 

THE  CONTINUATION  OF  TODD  &  BOWxMAN^S  PHYSIOLOGY, 

beautifully  illustrated  on  wood. 

1^"  Subscribers  for  1853,  who  do  not  possess  the  commencement  of  Todd  and  Bowman  can 
obtain  it,  in  a  handsome  octavo  volume,  of  552  pages,  with  over  150  illustrations,  by  mail,  free  of 
postage,  on  a  remittance  of  $2  50  to  the  publishers. 


It  will  thus  be  seen  that  for  the  small  sum  of  FIVE  DOLLARS,  paid  in  advance,  the  subscriber 
will  obtain  a  Quarterly  and  a  Monthly  periodical, 

EMBRACING  ABOUT  FIFTEEN  HUNDRED  LARGE  OCTAVO  PAGES 

mailed  to  any  part  of  the  United  States,  free  of  postage. 

These  very  favorable  terras  are  now  presented  by  the  publishers  with  the  view  of  removing  all 
difficulties  and  objections  to  a  full  and  extended  circulation  of  the  Medical  Journal  to  the  office  of 
every  member  of  the  profession  throughout  the  United  Slates.  The  rapid  extension  of  mail  facili- 
ties, will  now  place  the  numbers  before  subscribers  with  a  certainty  and  dispaKrh  not  hertofbre 
attainable;  while  by  the  system  now  proposed,  every  subscriber  throughout  the  Union  is  placed 
upon  an  equal  footing,  at  the  very  reasonable  price  of  Five  Dollars  for  two  periodicals,  without 
further  expense. 

Those  subscribers  who  do  not  pay  in  advance  will  bear  in  mind  that  their  subscription  of  Five 
Dollars  will  entitle  them  to  the  Journal  only,  without  the  News,  and  that  they  will  be  at  the  expense 
of  their  own  postage  on  the  receipt  of  each  number.  The  advantage  of  a  remittance  when  order- 
ing the  Journal  will  thus  be  apparent. 

As  the  Medical  News  and  Library  is  in  no  case  sent  without  advance  payment,  its  subscribers 
will  always  receive  it  free  of  postage. 

It  should  also  be  borne  in  mind  that  the  publishers  will  now  take  the  risk  of  remittances  by  mail, 
only  requiring,  in  cases  of  loss,  a  certificate  from  the  subscriber's  Postmaster,  that  the  money  was 
duly  mailed  and  forwarded 

^^  Funds  at  par  at  the  subscriber's  place  of  residence  received  in  payment  of  subscriptions. 

Address,  BLANCHARD  &  LEA,  Philadelphia. 


AND    SCIENTIFIC    PUBLICATIONS. 


ASHWELL   (SAMUEL),   M.  D. 
A  PRACTICAL  TREATISE  ON  THE  DISEASES  PECULIAR  TO  WOMEN. 

Illustrated  by  Cases  derived  from  Hospital  and  Private  Practice.    "With  Additions  by  Paul  Beck 
GoDDARD,  M.  D.     Second  American  edition.     lu  one  octavo  volume,  of  520  pages. 


One  of  the  very  best  works  ever  issued  from  the 
press  on  the  diseases  of  females. — Western  Lancet. 


This  is  an  invaluable  work. 
and  Surgical  Journal. 


■Missouri  Medical 


We  strongly  recommend  Dr.  Ashwell's  Treatise 
to  our  readers  as  a  valuable  book  of  reference,  on  an 
extensive,  complicated,  and  highly  important  class 
of  diseases — Edinburgh  Monthly  Journal  of  Med. 
Sciences. 


ARNOTT    (NEILL),  M.  D. 
OF    PHYSICS  J    or  Natural  Philosophy,   General  and  Medical. 


ELEMENTS 

Written  for  universal  use,  in  plain  or  non-technical  language 
M.  D.     Complete  in  one  octavo  volume,  of  484  page 


A  new  edition,  by  Isaac  Hays, 
with  about  two  hundred  illustrations. 


ABERCROMBIE   (JOHN),  M.  D. 
PATHOLOGICAL  AND  PRACTICAL  RESEARCHES  ON  DISEASES  OF 

THE  STOMACH,  INTESTINAL  CANAL,  &c.     Fourth  edition,  in  one  small  octavo  volume, 

of  260  pages. 


BENNETT   (HENRY),  M.  D. 
A  PRACTICAL   TREATISE    ON   INFLAMMATION  OF   THE   UTERUS 

AND  ITS  APPENDAGES,  and  on  Ulceration  and  Induration  of  the  Neck  of  the  Uterus.   Third 
edition.     In  one  neat  octavo  volume,  of  350  pages,  with  wood-cuts. 


We  shall  not  call  it  a  second  edition,  because,  as 
Dr.  Bennett  truly  observes,  it  is  really  a  new  work. 
It  will  be  found  "to  contain  not  only  a'faithfal  histo- 
ry of  the  various  pathological  changes  produced  by 
inflammation  in  the  uterus  and  its  annexed  organs, 
in  the  different  phases  of  female  life,  but  also  an  ac- 
curate analysis  of  the  influence  exercised  by  inflam- 
mation in  the  production  of  the  various  morbid  con- 
ditions of  the  uterine  system,  hitherto  described  and 
treated  as  functional. — Britishand  Foreign  Medico- 
Chirurgical  Review. 

Few  Avorks  issue  from  the  medical  press  which 
are  at  once  original  and  sound  in  doctrine  ;  but  such, 
we  feel  assured,  is  the  admirable  treatise  now  before 


us.  The  important  practical  precepts  which  the 
author  inculcates  are  all  rigidly  deduced  from  facts. 
.  .  .  Every  page  of  the  book  is  good,  and  eminently 
practical.  .  .  .  So  far  as  we  know  and  believe,  it  is 
the  best  work  on  the  subject  of  which  it  treats. — 
Monthly  Journal  of  Medical  Science. 

We  refer  our  readers  with  satisfaction  to  this  work 
for  information  on  a  hitherto  most  obscure  and  diffi- 
cult class  of  diseases. — London  Medical  Gazette. 

One  of  the  best  practical  monographs  amongst 
modern  English  medical  books. — Transylvania  Med. 
Journal. 


BE  ALE  (LIONEL   JOH  N),  M.  R.  C.  S.,  Sec, 
THE    LAWS   OF    HEALTH    IN   RELATION   TO    MIND    AND   BODY. 

A  Series  of  Letters  from  an  old  Practitioner  to  a  Patient.     In  one  handsome  volume,  royal  12mo., 
extra  cloth. 


BILLING    (ARCHIBALD),  M.  D. 
THE  PRINCIPLES  OF  MEDICINE.     Second  American,  from  the  Fifth  and 

Improved  London  edition.     In  one  handsome  octavo  volume,  extra  cloth,  250  pages. 


BLAKISTON. (PEYTON),  M 
PRACTICAL    OBSERVATIONS    ON 

CHEST,  and  on  the  Principles  of  Auscultation. 


,  F.  R.  S.,  &.C. 
CERTAIN    DISEASES 

In  one  volume,  Svo.,  pp.  384. 


OF    THE 


BENEDICT  (N.   D.),  M.  D. 
COMPENDIUM   OF   LECTURES   ON   THE  THEORY   AND  PRACTICE 

OF  MEDICINE,  delivered  by  Professor  Chapman  in  the  University  of  Pennsylvania.    In  one 
octavo  volume,  of  258  pages. 


BURROWS   (GEORGE),  M.  D. 
ON  DISORDERS  OF  THE  CEREBRAL   CIRCULATION,  and  on  the  Con- 

nection  between  the  Affections  of  the  Brain  and  Diseases  o(  the  Heart.    In  one  Svo.  vol.,  with 
colored  plates,  pp.  21 1). 


BLANCHARD   &    LEA'S   MEDICAL 


BUDD  (GEORGE),  M.  D.,  F.  R.  S., 

Professor  of  Medicine,  in  King's  College,  London. 

ON  DISEASES  OF  THE  LIVER.  Second  American,  from  the  second  and 
enlarged  Lontlon  edition.  In  one  very  handsome  octavo  volume,  with  four  beautifully  colored 
plates,  and  numerous  wood-cuts.    pp.  468.    New  edition.     {Now  Ready.) 

The  reputation  which  this  work  has  obtained  as  a  full  and  practical  treatise  on  an  important  class 
of  diseases  will  not  be  diminished  by  this  improved  and  enlarged  edition.  It  has  been  carefully  and 
thoroughly  revised  by  the  author ;  the  number  of  plates  has  been  increased,  and  the  style  of  its  me- 
chanical execution  will  be  found  materially  improved. 


The  full  digest  we  have  given  of  the  new  matter 
introduced  into  ihe  present,  volume,  is  evidence  of 
the  value  we  place  on  it.  The  fact  lliat  the  profes- 
sion has  required  a  second  edition  of  a  monograph 
such  as  that  before  us,  bears  honorable  testimony 
to  its  usefulness.  For  many  years,  Dr.  JBudd's 
work  must  be  the  authority  of  the  great  mass  of 
British  practitioners  on  the  hepatic  diseases  ;  and  it 
is  satisfactory  that  the  subject  has  been  taken  up  by 
so  able  and  experienced  a  physician. — British  and 
Foreign  Medico-Chirurgical  Review. 

We  cannot  too  strongly  recommend  the  diligent 
study  of  this  volume.  The  work  cannot  fail  to  rank 
the  name  of  its  author  among  the  most  enlightened 
pathologists  and  soundest  practitioners  of  the  day. 
— Medico-C hirurgical  Review. 


We  feel  bound  to  sny  that  Dr.  Budd"s  treatise  is 
greatly  in  advance  of  its  predecessors.  It  is  the  first 
work  in  wliich  the  results  of  microscopical  anatomy 
and  tlie  discoveries  of  modern  chemistry  have  been 
brought  fully  to  bear  upon  the  pathology  and  treat- 
ment of  diseases  of  the  liver;  and  it  is  the  only  work 
in  which  a  method  of  studying  diseases  of  this  organ, 
founded  upon  strictly  inductive  principles,  is  de- 
veloped.—X>M/j^m  Medical  Press. 

Having  thus  attempted  to  give  a  brief  summary  of 
the  more  important  ccmtents  of  this  work,  we  would, 
in  conclusion,  recommend  it  to  every  practitioner 
and  student  as  well  worthy  of  a  careful  and  patient 
perusal.— TAe  New  Orleans  Medical  and  Surgical 
Journal. 


BLOOD  AND   URINE  (MANUALS  ON). 
BY  JOHN  WILLIAM   GRIFFITH,   a.  OWEN  REESE,   AND  ALFRED 

MARKWICK.     One  thick  volume,  royal  r2mo.,  extra  cloth,  with  plates,    pp.  460. 


BRIGHAM   (AMARIAH),  M.D. 
ON  MENTAL  CULTIVATION  AND  EXCITEMENT.     In  one  neat  volume, 

18mo.,  extra  cloth. 


BRODIE  (SIR  BENJAMIN  C),  M.  D.,  &,c. 
CLINICAL  LECTURES  ON  SURGERY.     1  vol.  8vo.,  cloth.     850  pp. 

BY   THE   SAME    ArTHOR. 

PATHOLOGICAL    AND    SURGICAL    OBSERVATIONS   ON   THE   DIS- 
EASES OF  THE  JOINTS.    1  vol.  8vo.,  cloth,    pp.  21G. 

BV   THE   SAME   AUTHOR. 

LECTURES  ON  THE  DISEASES  OF  THE  URINARY  ORGANS.     1  vol. 

8vo.,  cloth,     pp.  214. 

*^*  These  three  works  may  be  had  neatly  bound  together,  forming;  a  larg-e  volume  of"  Brodie's 
Surgical  Works."    pp.  780. 


BIRD  (GOLDING),  A.  M.,  M.  D.,  &,c. 
URINARY     DEPOSITS:     THEIR     DIAGNOSIS,    PATHOLOGY,    AND 

THERAPEUTICAL  INDICATIONS.    A  new  American,  from  the  tiiird  and  improved  Londoa 
edition.    "With  over  sixty  illustrations.     In  one  royal  12mo.  volume,  extra  cloth,     pp.  338. 
The  new  edition  of  Dr.  Bird's  work,  though  not 
increased   in   size,  has  been  greatly  modified,  and 
much  of  it  rewritten.     It  now  presents,  in  a  com- 
pendious form,  the  gist  of  all  that  is  known  and  re 


liahle  in  this  department.  From  its  terse  style  and 
convenient  size,  it  is  particularly  applicable  to  tlie 
student,  to  whom  we  cordially  commend  it.— The 
Medical  Examiner. 

It  can  scarcely  be  necessary  for  us  to  say  anything 
of  the  merits  of  this  well-known  Treatise,  which  so 
admirably  brings  into  practical  applicaticm  the  re- 
sults of  tliose  microscopical  and  chemical  researches 
regarding  the  physiology  and  pathology  of  the  uri- 


nary secretion,  which  have  contributed  so  much  to 
the  increase  of  our  diagnostic  powers,  and  to  tlie 
extension  and  satisfactory  employment  of  our  thera- 
peutic resources.  In  the  preparation  of  this  new 
edition  of  his  work,  it  is  obvious  that  Dr.  Golding 
Bird  has  spared  no  pains  to  render  it  a  faithful  repre- 
sentation of  the  present  state  of  scientific  knowledge 
on  the  subject  it  embraces. 

Although,  of  course,  there  are  many  topics  which 
are  open  to  differences  of  opinion,  we  cannot  point 
to  any  well-substantiated  result  of  inquiry  whicii 
the  author  has  overlooked.—  The  British  and  Foreign 
Medico-C  hirurgical  Review. 


BY   THE   SAME   AUTHOR. 

ELEMENTS  OF  NATURAL  PHILOSOPHY;   being  au  Experimental  Intro- 

duction  to  the  Physical  Sciences.     Illustrated  with  nearly  four  hundred  wood-cuts.    From  the 
third  London  edition.     In  one  neat  volume,  royal  12mo.     pp.  402. 


AND   SCIENTIFIC    PUBLICATIONS. 


BARTLETT  (ELISHA),  M.  D., 

Professor  of  Materia  Medica  and  Medical  Jurisprudence  in  the  College  of  Physicians  and 
Surgeons,  New  York. 

THE   HISTORY,  DIAGNOSIS,   AND  TREATMENT   OP  THE   FEVERS 

OF  THE  UNITED  STATES.     Third  edition,  revised  and  improved.    In  one  octavo  volume, 
cff  six  hundred  pages,  beautifully  printed,  and  strongly  bound. 

In  preparing  a  new  edition  of  this  standard  work,  the  author  has  availed  himself  of  such  obser- 
vations and  investigations  as  have  appeared  since  the  publication  of  his  last  revision,  and  he  has 
endeavored  in  every  way  to  render  it  worthy  of  a  continuance  of  the  very  marked  favor  with  which 
it  has  been  hitherto  received. 

The  masterly  and  elegant  treatise,  by  Dr.  Bartlett 
is  invaluable  to  the  American  student  and  practi- 
tioner.— Dr.  Holmes- s  Report  to  the  Nat.  Med.  Asso- 
ciation. 

We  regard  it,  from  the  examination  we  have  made 
of  it,  the  best  work  on  fevers  extant  in  our  language, 
and  as  such  cordially  recommend  it  to  the  medical 
public. — St.  Louis  Medical  and  Surgical  Journal. 


Take  it  altogether,  it  is  the  most  complete  history 
of  our  fevers  which  has  yet  been  published,  and 
every  practitioner  should  avail  himself  of  its  con- 
tents.—TAe  Western  Lancet. 


Of  the  value  and  importance  of  such  a  work,  it  is 
needless  here  to  speak  ;  the  profession  of  the  United 
States  owe  much  to  the  author  for  the  very  able 
volume  which  he  has  presented  to  them,  and  for  the 
careful  and  judicious  manner  in  which  he  has  exe- 
cuted his  t;isk.  No  one  volume  with  which  we  are 
acquainted  contains  so  complete  a  history  of  our 
fevers  as  this.  To  Dr.  Bartlett  we  owe  our  best 
thanks  for  the  very  able  volume  he  has  given  us,  as 
embodying  certainly  the  most  complete,  methodical, 
and  satisfactory  account  of  our  fevers  anywhere  to 
be  met  with.— The  Charleston  Med.  Journal  and 
Review. 


BY  THE  SAME  AUTHOR. 

AN  INQUIRY  INTO   THE   DEGREE   OF   CERTAINTY  IN   MEDICINE, 

and  into  the  Nature  and  Extent  of  its  Power  over  Disease.     In  one  volume,  royal  12mo.    pp.  84. 


BOWMAN  (JOHN   EJ,  M.D. 
PRACTICAL   HANDBOOK   OF   MEDICAL    CHEMISTRY.     In  one  neat 

volume,  royal  12mo.,  with  numerous  illustrations,     pp.  288. 

BY  THE  SAME  AUTHOR. 

INTRODUCTION    TO    PRACTICAL    CHEMISTRY,    INCLUDING    ANA- 

LYSIS.    With  numerous  illustrations.     In  one  neat  volume,  royal  12mo.     pp.  350. 


COLOMBAT  DE  L'ISERE. 
A  TREATISE   ON    THE    DISEASES    OF   FEMALES,  and  on  the  Special 

Hyg-iene  of  their  Sex.  Translated,  with  many  Notes  and  Additions,  by  C.  D.  Meigs,  M.  D. 
Second  edition,  revised  and  improved.  In  one  large  volume,  octavo,  wilt  numerous  wood-cuts, 
pp.  720. 


The  treatise  of  M.  Colombat  is  a  learned  and  la- 
borious commentary  on  these  diseases,  indicating 
very  considerable  research,  great  accuracy  of  judg- 
ment, and  no  inconsiderable  personal  experience. 
With  the  copious  notes  and  additions  of  its  experi- 
enced and  very  erudite  translator  and  editor.  Dr. 
Meigs,  it  presents,  probably,  one  of  the  most  com- 
plete and  comprehensive  works  on  the  subject  we  i  leans  Medical  Journal 
possess. — American  Med.  Journal. 


M.  Colombat  De  L'lsere  has  not  consecrated  ten 
years  of  studious  toil  and  research  to  the  frailer  sex 
in  vain;  and  although  we  regret  to  hear  it  is  at  the 
expense  of  health,  he  has  imposed  a  debt  of  gratitude 
as  well  upon  the  profession,  as  upon  the  mothers  and 
daughters  of  beautiful  France,  which  that  gallant 
nation  knows  best  how  to  acknowledge.— iVeio  Or- 


COPLAND  (JAMES),  M.  D.,  F.  R.  S.,  Sec. 
OF   THE   CAUSES,  NATURE,   AND   TREATMENT   OF    PALSY    AND 

APOPLEXY,  and  of  the  Forms,  Seats,  Complications,  and  Morbid  Relations  of  Paralytic  and 
Apoplectic  Diseases.     In  one  volume,  royal  12mo.,  extra  cloth,    pp.  32G. 


LECTURES 

la  one  neat  8vo 


CHAPMAN  (PROFESSOR  N.),  M.  D.,  &,c. 
ON    FEVERS,    DROPSY,    GOUT,   RHEUMATISM,    &c.  &c. 

.  volume,     pp.  450. 


CLYMER  (MEREDITH),  M.  D.,  &,c. 
FEVERS;     THEIR    DIAGNOSIS,    PATHOLOGY,    AND    TREATMENT. 

Prepared  and  Edited,  with  large  Additions,  from  ihe  Essays  on  Fever  in  Tweedie's  Library  of 
Practical  Medicine.     In  one  octavo  volume,  of  600  pages. 


CARSON  (JOSEPH),  M.  D., 

Professor  of  Materia  Medica  and  Pharmacy  in  the  University  of  Pennsylvania. 

SYNOPSIS  OF  THE  COURSE  OF  LECTURES  ON  MATERIA  MEDICA 

AND  PHARMACY,  delivered  in  the  University  of  Pennsylvania.    In  one  very  neal  octavo 
volume,  of  208  pages. 


ELANCHARD  &  LEA'S   MEDICAL 


CARPENTER  (WILLIAM   B.),  M.  D.,  F.  R.  S.,  &c., 

Examiner  in  Physiology  and  Comparative  Anatomy  in  the  University  of  London. 

PRINCIPLES  OF  HUMAN  PHYSIOLOGY;  with  their  chief  applications  to 

Psychology,  Pathology,  Therapeutics,  Hygiene,  and  Forensic  Medicine.  Fifth  American,  from 
the'  fourth  and  enlarged  London  edition.  "With  three  hundred  and  fourteen  illustrations.  Edited, 
with  additions,  by  Francis  Gurney  Smith,  M.D.,  Professor  of  the  Institutes  of  Medicine  in  the 
Pennsylvania  Medical  College,  &c.  In  one  very  large  and  beautiful  octavo  volume,  of  about  1100 
large  pages,  handsomely  printed  and  strongly  bound  in  leather,  with  raised  bands.  New  edition. 
{Just  Issued.) 

From  the  Author'' s  Preface  to  the  present  Edition. 

"  When  the  author,  on  the  completion  of  his  '  Principles  of  General  and  Comparative  Physiology,' 
applied  himself  to  the  preparation  of  his  <  Principles  of  Human  Physiology,'  for  the  press,  he  found 
that  nothing  sliort  of  a«  entire  remodelling  of  the  preceding  edition  would  in  any  degree  satisfy  his 
notions  of  what  such  a  treatise  ought  to  be.  For  although  no  fundamental  change  had  taken  place 
during  the  interval  in  the  fabric  ot  Physiological  Science,  yet  a  large  number'of  less  important 
modifications  had  been  effected,  which  had  combined  to  produce  a  very  considerable  alteration  in 
its  aspect.  Moreover,  the  progressive  maturation  of  his  own  views,  aiid  his  increased  experience 
as  a  teacher,  had  not  only  rendered  him  more  keenly  alive  to  the  imperfections  which  were  inherent 
in  its  original  plan,  but  had  caused  him  to  look  upon  many  topics  in  a  light  very  different  from  that 
under  which  he  had  previously  regarded  them  ;  and,  in  particular,  he  felt  a  strong  desire  to  give  to 
his  work  as  ^jrac^trai  a  character  as  possible,  without  foregoing  the  position  which  (he  trusts  he 
may  say  without  presumption)  he  had  succeeded  in  gaining  for  it,  as  a  philosophical  ey^^oi^mon  of 
one  important  department  of  Physiological  Science.  He  was  led,  therefore,  to  the  determination 
of,  in  reality,  producing  a  new  treatise,  in  which  only  those  parts  of  the  old  should  be  retained, 
which  might  express  the  existing  state  of  knowledge,  and  of  his  own  opinions  on  the  points  to  which 
they  relate." 

The  American  edition  has  been  printed  from  sheets  prepared  for  the  purpose  by  the  author,  who 
has  introduced  nearly  one  hundred  illustrations  not  in  the  London  edition  ;  while  it  has  also  enjoyed 
the  advantage  of  a  careful  superintendence  on  the  part  of  the  editor,  who  has  added  notices  of  such 
more  recent  investigations  as  had  escaped  the  author's  attention.  Neither  care  nor  expense  has 
l)een  spared  in  the  mechanical  execution  of  the  work  to  render  it  superior  to  former  editions,  and  it 
IS  confidently  presented  as  in  every  way  one  of  the  handsomest  volumes  as  yet  placed  before  the 
medical  profession  in  this  country. 


The  most  complete  work  on  the  science  in  our 
language. — Am.  Med.  Journal. 

The  most  complete  exposition  of  physiology  which 
any  language  can  at  present  give. — Brit,  and  For. 
Med.-Cfiirurg.  Review. 

We  have  thus  adverted  to  some  of  the  leading 
•'additions  and  alterations,"  which  have  been  in- 
troduced by  the  author  into  this  edition  of  his  phy- 
siology. These  will  be  found,  however,  very  far  to 
exceed  the  ordinary  limits  of  a  new  edition,  "the 
old  materials  having  been  incorporated  with  the 
new,  rather  than  the  new  with  the  old."  It  now 
certainly  presents  the  most  complete  treatise  on  the 
subject  within  the  reach  of  the  American  reader  ; 
and  while,  for  availability  as  a  text-book,  we  may 
perhaps  regret  its  growth  in  bulk,  we  are  sure  that 
the  student  of  physiology  will  feel  the  impossibility 
of  presenting  a  thorough  digest  of  the  facts  of  the 
science  within  a  more  limited  compass. — Medical 
Examiner. 

The  greatest,  the  most  reliable,  and  the  best  book 
on  the  subject  which  we  know  of  in  the  English 
language. — Stethoscope. 

The  most  comjjlete  work  now  extant  in  our  lan- 
guage.— N.  O.  Med.  Register. 

We  do  not  hesitate  a  moment  in  pronouncing  it 
the  besl  text  l)o<)k  in  the  Englisli  language.  Jn  this 
new  edition,  the  author  has  again  displayed  his  great 
zeal.  The  work  is  almost  a  new  one,  having  been 
entirely  remodelled;  avast  amount  of  valuable  ma- 
terial has  been  added,  and  with  great  propriety,  as- 
signed its  appropriate  place.— 5«.  Louis  Med.  and 
Surg.  Journal. 

The  best  text-book  in  the  language  on  this  ex- 
tensive subject. — London  Med.  Times. 

A  complete  cyclopaedia  of  this  branch  of  science. 
—N.  Y.  Med.  Times. 


The  standard  of  authority  on  physiological  sub- 
jects. #  #  *  In  the  present  edition,  to  particularize 
the  alterations  and  additions  which  have  been  made, 
would  require  a  review  of  the  vi'hole  work,  since 
scarcely  a  subject  has  not  been  revised  and  altered, 
added  to,  or  entirely  remodelled  to  adapt  it  to  the 
present  state  of  the  science. — Charleston  Med.  Journ . 

The  changes  are  too  numerous  to  admit  of  an  ex- 
tended notice  in  this  place.  At  every  point  where 
the  recent  diligent  labors  of  organic  chemists  and 
micrographers  have  furnished  interesting  and  valu- 
able facts,  they  have  been  appropriated,  and  no  pains 
have  been  spared,  in  so  incorporating  and  arranging 
them  that  the  work  may  constitute  one  harmonious 
system. — Southern  Med.  and  Surg.  Journal. 

Any  reader  who  desires  a  treatise  on  physiology 
may  feel  himself  entirely  safe  in  ordering  this. — 
Western  Med.  and  Surg.  Journal. 

From  this  hasty  and  imperfect  allusion  it  Mill  be 
seen  by  our  readers  that  the  alterations  and  addi- 
tions to  this  edition  render  it  almost  a  new  work — 
and  we  can  assure  our  readers  that  it  is  one  of  the 
best  summaries  of  the  existing  facts  of  physiological 
science  within  the  reach  of  the  English  student  and 
physician. — N.  Y.  Journal  of  Medicine. 

The  profession  of  this  country,  and  perhaps  also 
of  Europe,  have  anxiously  and  for  some  time  awaited 
the  announcement  of  this  new  editi<m  of  Carpenter's 
Human  Physiology.  His  former  editions  have  for 
many  years  been  almost  the  only  text-book  on  Phy- 
siology in  all  our  medical  schools,  and  its  circula- 
tion among  the  profession  has  been  unsurpassed  by 
any  work  in  any  department  of  medical  science. 

it  is  quite  unnecessary  for  us  to  speak  of  this 
work  as  its  merits  would  justify.  The  mere  an 
nouncement  of  its  appearance  will  afford  the  highest 
pleasure  to  every  student  of  Physiology,  while  its 
perusal  will  be  of  infinite  service  in  advancing 
physiological  science. — Ohio  Med.  and  Surg.  Journ. 


BY    THE   SAME   AUTHOR. 

PRINCIPLES    OF    GENERAL    AND    COMPARATIVE    PHYSIOLOGY. 

Intended  as  an  Introduction  to  the  Study  of  Human  Physiologv:  and  as  a  Guide  to  the  Philo- 
sophical pursuit  of  Natural  History.    New  and  improved  edilion,\preparing.) 


AND    SCIENTIFIC    PUBLICATIONS. 


CARPENTER  (WILLIAM  B.),   M.  D.,  F.  R.  S., 

Examiner  in  Physiology  and  Comparative  Anatomy  in  the  University  of  London. 

ELEMENTS  (OR  MANUAL)  OF  PHYSIOLOGY,  INCLUDINa  PHYSIO- 

LOGICAL  ANATOMY.     Second  American,  from  a  new  and  revised  London  edition.    With, 
one  hundred  and  ninety  illustrations.     In  one  very  handsome  octavo  volume.     {Lately  Issued.) 

In  publishing  the  first  edition  of  this  work,  its  title  was  altered  from  that  of  the  London  volume, 
by  the  substitution  of  the  word  "Elements"'  for  that  of  <'  Manual,"  and  with  the  author's  sanction 
the  title  of  "Elements"  is  still  retained  as  being  more  expressive  of  the  scope  of  the  treatise.  A 
comparison  of  the  present  edition  with  the  former  one  will  show  a  material  improvement,  the 
author  having  revised  it  thoroughly,  with  a  view  of  rendering  it  completely  on  a  level  with  the 
most  advanced  state  of  the  science.  By  condensing  the  less  important  portions,  these  numerous 
additions  have  been  introduced  without  materially  increasing  the  bulk  of  the  volume,  and  while 
numerous  illustrations  have  been  added,  and  the  general  execution  of  the  work  improved,  it  has 
been  kept  at  its  former  very  moderate  price. 


To  say  that  it  is  the  best  manual  of  Physiology 
now  before  the  public.  Avould  not  do  sufficient  justice 
to  the  author. — Buffalo  Medical  Journal. 

In  his  former  works  it  would  seem  that  he  had 
exhausted  the  subject  of  Physiology.  In  the  present, 
he  gives  the  essence,  as  it  were,  of  the  whole. — N.  Y. 
Journal  of  Medicine. 

Those  who  have  occasion  for  an  elementary  trea- 
tise on  Physiology,  cannot  do  better  than  to  possess 
themselves  of  the  manual  of  Dr.  Carpenter. — Medical 
Examiner. 


The  best  and  most  complete  expos6  of  modern 
Physiology,  m  one  volume,  extant  in  the  English 
language. — St.  Louis  Medical  Journal. 

With  such  an  aid  in  his  hand,  there  is  no  excuse 
for  the  ignorance  often  displayed  respecting  the  sub- 
jects of  which  it  treats.  From  its  unpretending  di- 
mensions, it  may  not  be  so  esteemed  by  those  anxious 
to  make  a  parade  of  their  erudition;  but  whoever 
rriasters  its  contents  will  have  reason  to  be  proud  of 
his  physiological  acquirements.  The  illustrations 
are  well  selected  and  finely  executed. — Dublin  Med, 
Press. 


BY    THE   SAME   ATTTHOR. 

A  PRIZE  ESSAY  ON  THE  USE  OF  ALCOHOLIC  LIQUORS  IN  HEALTH 

AND  DISEASE.    In  one  neat  12mo.  volume. 

BY  THE  SAME  AUTHOR.     {Preparing.) 

THE  MICROSCOPE  AND  ITS  REVELATIONS.     In  one  handsome  volume, 

beautifully  illustrated  with  plates  and  wood-cuts. 


CHELIUS  (J.  M.),   M.  D., 

Professor  of  Surgery  in  the  University  of  Heidelberg,  &c. 

A  SYSTEM  OF  SURGERY.     Translated  from  the  German,  and  accompanied 

with  additional  Notes  and  References,  by  John  F.  South.     Complete  in  three  very  large  octavo 
volumes,  of  nearly  2200  pages,  strongly  bound,  with  raised  bands  and  double  titles. 


We  do  not  hesitate  to  pronounce  it  the  best  and 
most  comprehensive  sj^stem  of  modern  surgery  with 
w^hich  we  are  acquainted. — Medico-C kirurgical  Re- 
view. 

The  fullest  and  ablest  digest  extant  of  all  that  re- 
lates to  the  present  advanced  state  of  surgical  pa- 
thology.— American  Medical  Journal. 

As  complete  as  any  system  of  Surgery  can  well 
be. — Southern  Medical  and  SurgicalJournal. 


The  most  learned  and  complete  systematic  treatise 
now  extant. — Edinburgh  Medical  Journal. 

A  complete  encyclopaedia  of  surgical  science — a 
very  complete  surgical  library— by  far  the  most 
complete  and  scientific  system  of  surgery  in  the 
English  language. — N.  Y.  Journal  0/ Medicine. 

The  most  extensive  and  comprehensive  account  of 
the  art  and  science  of  Surgery  in  our  language. — 
Lancet. 


CHRISTISON  (ROBERT),  M.  D.,  V.  P.  R.  S.  E.,  &,c. 
A  DISPENSATORY;  or,  Commentary  on  the  Pharmacopoeias  of  Great  Britain 

and  the  United  States;  comprising  the  Natural  History,  Description,  Chemistry,  Pharmacy,  Ac- 
tions, Uses,  and  Doses  of  the  Articles  of  the  Materia  Medica.  Second  edition,  revised  and  im- 
proved, with  a  Supplement  containing  the  most  important  New  Remedies.  With  copious  Addi- 
tions, and  two  hundred  and  thirteen  large  wood-engravings.  By  R.  Eglesfeld  Griffith,  M.  D. 
In  one  very  large  and  handsome  octavo  volume,  of  over  1000  pages. 

It  is  not  needful  that  we  should  compare  it  with 
the  other  pharmacopoeias  extant,  which  enjoy  and 
merit  the  confidence  of  the  professicm  :  it  is  enough 
to  say  that  it  appears  to  us  as  perfect  as  a  Dispensa- 
tory, in  the  present  state  of  pharmaceutical  science, 
could  be  made.  If  it  omits  any  details  pertaining  to 
this  branch  of  knowledge  which  the  student  has  a 
right  to  expect  in  such  a  work,  we  confess  the  omis- 
sion has  escaped  our  scrutiny.  We  cordially  recom- 
mend this  work  to  such  of  our  readers  as  are  in  need 
of  a  Dispensatory.  They  cannot  make  choice  of  a 
better. — Western  Journ.  of  Medicine  and  Surgery. 


There  is  not  in  any  language  a  more  complete  and 
perfect  Treatise. — iV.  Y.  Annalist. 

In  conclusion,  we  need  scarcely  say  that  we 
strongly  recommend  this  work  to  all  classes  of  our 
readers.  Asa  Dispensatory  and  commentary  on  the 
Pharmacopoeias,  it  is  unrivalled  in  the  English  or 
any  other  language.— 7'Afi  Dublin  Quarterly  Journal. 

We  earnestly  recommend  Dr.  Christison's  Dis- 
pensatory to  all  our  readers,  as  an  indispensable 
companion,  not  in  the  Study  only,  but  in  the  Surgery 
also. — British  and  Foreign  Medical  Review. 


BLANCHARD  &  LEA'S   MEDICAL 


CONDIE  (D.  F.),  M.  D.,  &c. 
A  PRACTICAL  TREATISE  ON  THE  DISEASES  OF  CHILDREN.    Third 

edition,  revised  and  augmented.    In  one  large  volume,  8vo.,  of  over  700  pages. 

Dr.  Condie's  scholarship,  acumen,  industry,  and 
practical  sense  are  manifested  in  this,  as  in  all  his 
numerous  contributions  to  science. — Dr.  Holnus^s 
Report  to  the  American  Medical  Association. 

Taken  as  a  whole,  in  our  judgment.  Dr.  Condie's 
Treatise  is  the  one  from  the  perusal  of  which  the 
practitioner  in  this  country  will  rise  with  the  great- 
est satisfaction  —Western  Journal  of  Medicine  and 
Surgery. 

One  of  the  best  works  upon  the  Diseases  of  Chil- 
dren in  the  English  language.— Western  Lancet. 

We  feel  assured  from  actual  experience  that  no 
physician's  library  can  be  complete  without  a  copy 
of  this  work.— iV.  Y.  Journal  of  Medicine. 

Perhaps  the  most  full  and  complete  work  noAV  be- 
fore the  profession  of  the  United  States;  indeed,  we 
may  say  in  the  English  language.  It  is  vastly  supe- 
rior to  most  of  its  predecessors. — Transylvania  Med. 
Journal. 

A  veritable  pjediatric  encyclopsedia,  and  an  honor 
to  American  medical  literature. — Ohio  Medical  and 
Surgical  Journal. 


Every  important  fact  that  has  been  verified  or 
developed  since  the  publication  of  the  previous  edi- 
tion, either  in  relation  to  the  nature,  diagnosis,  or 
treatment  of  the  diseases  of  children,  has  been  ar- 
ranged and  incorporated  into  the  body  of  the  work  ; 
thus  posting  up  to  date,  to  use  a  counting-house 
plirase,  all  the  valuable  facts  and  useful  information 
on  the  subject.  To  the  American  practitioner.  Dr. 
Condie's  remarks  on  the  diseases  of  children  will 
be  invaluable,  and  we  accordingly  advise  those 
who  have  failed  to  read  this  work  to  procure  a  copy, 
and  niake  themselves  familiar  with  its  sound  princi- 
ples.— The  Neiv  Orleans  Med.  and  Surg.  Journal. 

We  feel  persuaded  that  the  American  medical  pro- 
fession will  soon  regard  it  not  only  as  a  very  good, 
but  as  the  very  best  "Practical  Treatise  on  the 
Diseases  of  Children." — American  Medical  Journal. 

We  pronounced  the  first  edition  to  be  the  best 
work  on  the  diseases  of  children  in  the  English 
language,  and,  notwithstanding  all  that  has  been 
published,  we  still  regard  it  in  that  V\g\\t.— Medical 
Examiner. 


COOPER  (BRANSBY  B.),  F.  R.  S., 

Senior  Surgeon  to  Guy's  Hospital,  &c. 

LECTURES  ON  THE   PRINCIPLES   AND   PRACTICE   OF   SURGERY. 

In  one  very  large  octavo  volume,  of  750  pages.    {Lately  Issued). 


For  twenty-five  years  Mr.  Bransby  Cooper  has 
been  surgeon  to  Guy's  Hospital;  and  the  volume 
before  us  may  be  said  to  consist  of  an  account  of 
the  results  of  his  surgical  experience  during  that 
long  period.  We  cordially  recommend  Mr.  Bransby 
Cooper's  Lectures  as  a  most  valual)le  addition  to 
our  surgical  literature,  and  one  which  cannot  fail 
to  be  of  service  both  to  students  and  to  those  who 
are  actively  engaged  in  the  practice  of  their  profes- 
sion.— The  Lancet. 

A  good  book  by  a  good  man  is  always  welcome  ; 
and  Mr.  Bransby  Cooper's  book  does  no  discredit  to 


its  paternity.  It  has  reminded  us,  in  its  easy  style 
and  copious  detail,  more  of  Watson's  Lectures,  than 
any  book  we  have  seen  lately,  and  we  should  not 
be  surprised  to  see  it  occupy  a  similar  position  to 
that  well-known  work  in  professional  estimation. 
It  consists  of  seventy-five  lectures  on  the  most  im- 
portant surgical  diseases.  To  analyze  such  a  work 
is  impossible,  while  so  interesting  is  every  lecture, 
that  we  feel  ourselves  really  at  a  loss  what  to  select 
for  quotation.  The  work  is  one  which  cannot  fail 
to  become  a  favorite  with  the  profession  ;  and  it  pro- 
mises to  supply  a  hiatus  which  the  student  of  sur- 
gery has  often  to  deplore. — Medical  Times. 


COOPER  (SIR  ASTLEY   P.),   F.  R.  S.,  8lc. 
A  TREATISE  ON  DISLOCATIONS  AND  FRACTURES  OF  THE  JOINTS. 

Edited  by  Bransby  B.  Cooper,  F.  R.  S.,  &:c.  With  additional  Observations  by  Prof.  J.  C. 
Warren.  A  new  American  edition.  In  one  handsome  octavo  volumcj  with  numerous  illustra- 
tions on  wood. 

BY   THE   SAME   AUTHOR. 

ON  THE  ANATOMY  AND  TREATMENT   OF   ABDOMINAL   HERNIA. 

One  large  volume,  imperial  8vo.,  with  over  130  lithographic  figures. 

BY   THE   SAME    AUTHOR. 

ON   THE   STRUCTURE   AND   DISEASES    OF  THE   TESTIS,  AND  ON 

THE  THYMUS  GLAND.    One  vol.  imperial  8vo.,  with  177  figures,  on  29  plates. 


BY   THE   SAME   AUTHOR. 

ON  THE  ANATOMY  AND  DISEASES   OF  THE   BREAST,  with  twentj- 

five  Miscellaneous  and  Surgical  Papers.     One  large  volume,  imperial  8vo.,  with  252  figures,  on 
36  plates. 

These  three  last  volumes  complete  the  surgical  writings  of  Sir  Astley  Cooper.  They  are  very 
handsomely  printed,  with  a  large  number  of  lithographic  plates,  executed  in  the  best  style,  and  are 
presented  at  exceedingly  low  prices. 


AND    SCIENTIFIC    PUBLICATIONS. 


CHURCHILL  (FLEETWOOD),  M.  D.,  M.  R.  I.  A. 
ON  THE  THEORY  AND  PRACTICE  OF  MIDWIFERY.  A  new  American, 

from  the  last  and  improved  English  edition.  Edited,  with  Notes  and  Additions,  by  D.  Francis 
CoNDiE,  M.  D..  author  of  a  <'i?ractical  Treatise  on  the  Diseases  of  Children,"  &c.  With  139 
illustrations.    In  one  very  handsome  octavo  volume,  pp.  510.     {Lately  Issued.) 


To  bestow  praise  on  a  book  that  has  received  such 
marked  approbation  would  be  superfluous.  We  need 
only  say,  therefore,  that  if  the  first  edition  was 
thouE^lit'  worthy  of  a  favorable  reception  by  the 
medical  public,  we  can  confidently  affirm  that  this 
will  be  found  much  more  so.  The  lecturer,  the 
practitioner,  and  the  student,  may  all  have  recourse 
to  its  pag-es,  and  derive  from  their  perusal  much  in- 
terest and  instruction  in  everythinp:  relatinpr  to  theo- 
retical and  practical  midwifery. — Dublin  Quarterly 
Journal  of  Medical  Science. 

A  work  of  very  great  merit,  and  such  as  we  can 
confidently  recommend  to  the  study  of  every  obste- 
tric practitioner. — London  Medical  Gazette. 

This  is  certainly  the  most  perfect  system  extant. 
It  is  the  best  adapted  for  the  purposes  of  a  text- 
book, and  that  which  he  whose  necessities  C(mfine 
him  to  one  book,  should  select  in  preference  to  all 
otliers. — Southern  Medical  and  Surgical  Journal. 

The  most  popular  work  on  midwifery  ever  issued 
from  the  American  press. — Charleston  Med.  Journal. 

Were  we  reduced  to  the  necessity  of  having  but 
one  work  on  midwifery,  and  permitted  to  choose, 
we  would  unhesitatingly  take  Churchill. — Western 
Med.  and  Surg.  Journal. 

It  is  impossible  to  conceive  a  more  useful  and 
elegant  manual  than  Dr.  Churchill's  Practice  of 
Midwifery. — Provincial  Medical  Journal. 

Certainly,  in  our  opinion,  the  very  best  work  on 
the  subject  which  exists.— iV.  Y.  Annalist. 


No  work  holds  a  higher  position,  or  is  more  de- 
serving of  being  placed  in  the  hands  of  the  tyro, 
the  advanced  student,  or  the  practitioner. — Medical 
Examiner. 

Previous  editions,  under  the  editorial  supervision 
of  Prof  R.  M.  Huston,  have  been  received  with 
marked  favor,  and  they  deserved  it;  but  this,  re- 
printed from  a  very  late  Dublin  edition,  carefully 
revised  and  brought  up  by  the  author  to  the  present 
time,  does  present  an  unusually  accurate  and  able 
exposition  of  every  important  particular  embraced 
in  the  department  of  midwifery.  *  *  The  clearness, 
directness,  and  precision  of  its  teachings,  together 
with  the  great  amount  of  statistical  research  which 
its  text  exhibits,  have  served  to  place  it  already  in 
the  foremost  rank  of  works  in  this  department  of  re- 
medial science. — N.  O.  Med.  and  Surg.  Journal. 

In  our  opinion,  it  forms  one  of  the  best  if  not  the 
very  best  text-book  and  epitome  of  obstetric  science 
whicli  we  at  present  possess  in  the  English  \'An- 
guage.— Monthly  Journal  of  Medical  Science. 

The  clearness  and  precision  of  style  in  which  it  is 
written,  and  the  great  amount  of  statistical  research 
wliich  it  contains,  have  served  to  place  it  in  the  first 
rank  of  works  in  this  department  of  medical  science. 
—  N.  Y.  Journal  of  Medicine. 

Few  treatises  will  be  found  better  adapted  as  a 
text-book  for  the  student,  or  as  a  manual  for  the 
frequent  consultation  of  the  young  practitioner. — 
American  Medical  Journal. 


BY   THE   SAME    AUTHOR. 


ON  THE  DISEASES  OF  INFANTS  AND  CHILDREN. 

handsome  volume  of  over  600  pages. 


In  one  large  and 


We  regard  this  volume  as  possessing  more  claims 
to  completeness  than  any  other  of  the  kind  with 
which  we  are  acquainted.  Most  cordially  and  earn- 
estly, therefore,  do  we  commend  it  to  our  profession- 
al brethren,  and  M''e  feel  assured  that  the  stamp  of 
their  approbation  will  indue  time  be  impressed  upon 
it.  After  an  attentive  perusal  of  its  contents,  we 
hesitate  not  to  say,  that  it  is  one  of  the  most  com- 
prehensive ever  written  upon  the  diseases  of  chil- 
dren, and  that,  for  copiousness  of  reference,  extent  of 
research,  and  perspicuity  of  detail,  it  is  scarcely  to 
be  equalled,  and  not  to  be  excelled,  in  any  lan- 
guage.— Dublin  Quarterly  Journal. 

After  tills  meagre,  and  we  know,  very  imperfect 
notice  of  Dr.  Churchiirs  work,  we  shall  conclude 
by  saying,  that  it  is  one  that  cannot  fail  from  its  co- 
piousness, extensive  research,  and  general  accuracy, 
to  exalt  still  higher  the  reputation  of  the  author  in 
this  country.  The  American  reader  will  be  particu- 
larly pleased  to  find  that  Dr.  Churchill  has  done  full 
justice  thnuigbout  his  work  to  the  various  American 
authors  on  this  subject.  The  names  of  Dewees, 
Eberle,  Condie,  and  Stewart,  occur  on  nearly  every 
page,  and  these  authors  are  constantly  referred  toby 
the  author  in  terms  of  the  highest  praise,  and  with 
the  most  liberal  courtesy. — the  Medical  Examiner. 


The  present  volume  will  sustain  the  reputation 
acquired  by  the  author  from  his  previous  works. 
The  reader  will  find  in  it  full  and  judicious  direc- 
tions for  the  management  of  infants  at  birth,  and  a 
compendious,  but  clear  account  of  the  diseases  to 
which  children  are  liable,  and  the  most  successful 
mode  of  treating  them.  We  must  not  close  this  no- 
tice without  calling  attention  to  the  author's  style, 
which  is  perspicuous  and  polished  to  a  degree,  we 
regret  to  say,  not  generally  characteristic  of  medical 
works.  We  recommend  the  work  of  Dr.  Churchill 
most  cordially,  both  to  students  and  practitioners, 
as  a  valuable  and  reliable  guide  in  the  treatment  of 
the  diseases  of  children. — Am,.  Journ.  of  the  Med. 
Sciences. 

We  know  of  no  work  on  this  department  of  Prac- 
tical Medicine  which  presents  so  candid  and  unpre- 
judiced a  statement  or  posting  up  of  our  actual 
knowledge  as4his. — N.  Y.  Journal  of  Medicine. 

Its  claims  to  merit  both  as  a  scientific  and  practi- 
cal work,  are  of  the  highest  order.  Whilst  we 
would  not  elevate  it  above  every  other  treatise  on 
the  same  subject,  we  certainly  believe  that  very  few 
are  equal  to  it,  and  none  superior. — Southern  Med. 
and  Surgical  Journal. 


BY  THE  SAME   AUTHOR. 


ESSAYS  ON  THE  PUERPERAL  FEVER,  AND  OTHER  DISEASES  PE- 

CULIAR  TO  WOMEN.     Selected  from  the  wrilingfs  of  British  Authors  previous  to  the  close  of 
the  Eighteenth  Century.    In  one  neat  octavo  volume,  of  about  four  hundred  and  fifty  pages. 


To  these  papers  Dr.  Churchill  has  appended  notes, 
embodying  whatever  information  has  been  laid  be- 
fore the  profession  since  their  authors"  time.  He  has 
also  prefixed  to  the  Essays  on  Puerperal  Fever, 
which  occupy  the  larger  portion  of  the  volume,  an 
interesting  historical   sketch  of  the  principal  epi- 


demics of  that  disease.  The  whole  forms  a  very 
valuable  collection  of  papers,  by  professional  writers 
of  eminence,  on  some  of  the  most  important  accidents 
to  which  the  puerperal  female  is  liable. — American 
Journal  of  Medical  Sciences. 


10 


BLANCHARD   &   LEA'S   MEDICAL 


CHURCHILL  (FLEETWOOD),    M.  D.,  M .  R.  I .  A.,    &.c. 

ON  THE  DISEASES  OF  WOMEN;  including  those  of  Pregnancy  and  Child- 
bed. A  new  American  edition,  revised  by  the  Author.  With  Notes  and  Additions,  by  D  Fran- 
cis CoNDiE,  M,  D.,  author  of  "  A  Practical  Treatise  on  the  Diseases  of  Children."  In  one  large 
and  handsome  octavo  volume,  vs^ith  wood-cuts,  pp.  684.     {Just  Issued.) 

From  the  Atithor^s  Preface. 
In  reviewing  this  edition,  at  the  request  of  my  American  publishers,  I  have  inserted  several  new 
sections  and  chapters,  and  I  have  added,  I  believe,  all  the  information  we  have  derived  from  recent 
researches;  in  addition  to  which  the  publishers  have  been  fortunate  enough  to  .«ecure  the  services 
of  an  able  and  highly  esteemed  editor  in  Dr.  Condie. 


We  now  regretfully  take  leave  of  Dr.  Churchill's 
book.  Had  our  typographical  limits  permitted,  \ve 
should  gladly  have  borrowed  more  from  its  richly 
stored  pages.  In  conclusion,  we  heartily  recom- 
mend it  to  the  profession,  and  would  at. the  same 
time  express  our  firm  conviction  that  it  will  not  only 
add  to  the  reputation  of  its  author,  but  will  prove  a 
work  of  great  and  extensive  utility  to  obstetric 
practitioners. — Dublin  Medical  Press. 

Former  editions  of  this  work  have  been  noticed  in 

I)reviousnumbersof  the  Journal.  The  sentiments  of 
ligh  commendation  expressed  in  those  notices,  have 
only  to  be  repeated  in  this;  not  from  the  fact  that 
the  profession  at  large  are  not  aware  of  the  high 
merits  which  this  work  really  possesses,  but  from  a 
desire  to  see  the  principles  and  doctrines  therein 
contained  more  generally  recognized,  and  more  uni- 
versally earned  out  in  practice. — N.  Y.  Journal  of 
Medicine, 

We  know  of  no  author  who  deserves  that  appro- 
bation, on  "the  diseases  of  females,"  to  the  same 
extent  that  Dr.  Churchill  does.  His,  indeed,  is  the 
only  thorough  treatise  we  know  of  on  the  subject; 
and  it  may  be  commended  to  practitioners  and  stu- 
dents as  a  masterpiece  in  its  particular  department. 
The  former  editions  of  this  work  have  been  com- 
mended strongly  in  this  journal,  and  they  have  won 
their  way  to  an  extended,  and  a  well-deserved  popu- 


larity. This  fifth  edition,  before  us.  is  well  calcu- 
lated to  maintain  Dr.  Churchill's  high  reputation. 
It  was  revised  and  enlarged  by  the  author,  for  his 
American  publishers,  and  it  seems  to  us  that  there  is 
scarcely  any  species  of  desirable  information  on  its 
subjects  that  may  not  be  found  in  this  work. — The 
Western  Journal  of  Medicijie  and  Surgery. 

AVe  are  gratified  to  announce  a  new  and  revised 
edition  of  Dr.  Churchill's  valuable  w^ork  on  the  dis- 
eases of  females  We  have  ever  regarded  it  as  one 
of  the  very  best  works  on  the  subjects  embraced 
within  its  scope,  in  the  English  language;  and  the 
present  edition,  enlarged  and  revised  by  the  author, 
renders  it  still  more  entitled  to  the  c(mfidence  of  the 
profession.  The  valuable  notes  of  Prof.  Huston 
liave  been  retained,  and  contril)ute,  in  no  small  de- 
gree, to  enhance  the  value  of  the  work.  It  is  a 
source  of  congratulation  that  the  publishers  have 
permitted  the  author  to  be,  in  this  instance,  his 
own  editor,  thus  securing  all  the  revision  which 
an  author  alone  is  capable  of  making. — The  Westerri 
Lancet. 

Asa  comprehensive  manual  for  students,  or  a 
work  of  reference  for  practitioners,  we  only  speak 
with  common  justice  when  we  say  that  it  surpasses 
any  other  that  has  ever  issued  on  the  same  sub- 
ject from  the  British  press. — The  Dublin  Quarterly 
Journal. 


DEWEES   (W.    P.),    M.D.,    &c. 

A  COMPREHENSIVE  SYSTEM  OF  MIDWIFERY.  Illustrated  by  occa- 
sional Cases  and  many  Engravings.  Twelfth  edition,  with  the  Author's  last  Improvements  and 
Corrections.     In  one  octavo  volume,  of  600  pages.     {Just  Issued.) 


BY   THE   SAME   AUTHOE. 


A  TREATISE  ON  THE  PHYSICAL  AND  MEDICAL  TREATMENT  OF 

CHILDREN.     Tenth  edition.     In  one  volume,  octavo,  548  pages.     {Just  Issiisd.) 


BY   THE   SAME   AUTHOR. 


A  TREATISE  ON   THE   DISEASES   OF   FEMALES.     Tenth   edition.     In 

one  volume,  octavo,  532  pages,  with  plates.     {Just  Issued.) 


DICKSON   (PROFESSOR   S.    H.),    M.D. 
ESSAYS  ON  LIFE,  SLEEP,   PAIN,   INTELLECTION,   HYGIENE,   AND 

DEATH.    In  one  very  handsome  volume,  royal  12mo. 


DANA   (JAMES    D). 


ZOOPHYTES  AND  CORALS.     In  one  volume,  imperial  quarto,  extra  cloth, 
with  wood-cuts.  ' 

ALSO, 

AN  ATLAS  TO  THE  ABOVE,  one  volume,  imperial  folio,  with  sixty-one  mag- 
nificent plates,  colored  after  nature.     Bound  in  half  morocco. 

ALSO, 

ON    THE    STRUCTURE    AND    CLASSIFICATION    OF    ZOOPHYTES. 

Sold  separate,  one  vol.,  cloth. 


DE    LA    BECHE    (SIR    HENRY    T.),    F.  R.  S.,  &c. 

THE  GEOLOGICAL  OBSERVER.     In  one  very  large   and  handsome  octavo 
volume,  of  700  pages.    With  over  three  hundred  wood-cuts.     {Just  Issued.) 


AND   SCIENTIFIC    PUBLICATIONS. 


11 


DRUITT   (ROBERT),   M.R.  C.S.,   8cc. 
THE  PRINCIPLES  AND  PRACTICE   OF  MODERN   SURGERY.     A  new 

American,  from  the  last  and  improved  London  edition.  Edited  by  F.  W.  Sargent,  M.  D., 
author  of  "  Minor  Surgery,"  &c.  Illustrated  wiih  one  hundred  and  ninety-three  wood-engrav- 
ings.   In  one  very  handsomely  printed  octavo  volume,  of  576  large  pages. 


No  work,  in  our  opinion,  equals  it  in  presenting 
so  much  valuable  surjjicul  matter  in  so  small  a 
compass. — St.  Louis  Med.  and  Surgical  Journal. 

Druitt's  Surgery  is  too  well  known  to  the  Ameri- 
can medical  profession  to  require  its  announcement 
anywhere.  Probably  no  work  of  the  kind  has  ever 
been  more  cordially  received  and  extensively  circu- 
lated than  this  The  fact  that  it  comprehends  in  a 
comparatively  small  compass,  all  the  essential  ele- 
ments of  theoretical  and  practical  Sursjery — that  it 
is  found  to  contain  reliable  and  authentic  informa- 
tion on  the  nature  and  treatment  of  nearly  all  surgi- 
cal affections — is  a  sufficient  reason  for  the  liberal 
patronage  it  has  obtained.  The  work  before  us  is  a 
new  edition,  greatly  enlarged  and  extended  by  the 
anthor — its  practical  part  having  undergone  a  tho- 
rough revision,  with  fifty  pages  of  additional  matter. 
The  editor,  Dr.  F.W.  Sargent,  of  Philadelphia,  has 
contributed  much  to  enhance  the  value  of  the  work, 
by  such  American  improvements  as  are  calculated 
more  perfectly  to  adapt  it  to  our  own  views  and 
practice  in  this  country.  It  abounds  everywhere 
with  spirited  and  life-like  illustrations,  which  to  the 
young  surgeon,  especially,  are  of  no  minor  consi- 
deration. Every  medical  man  frequently  needs  just 
such  a  work  as  this,  for  immediate  reference  in  mo- 
ments of  sudden  emergency,  when  he  has  not  time  to 
consult  more  elaborate  treatises.  Its  mechanical 
execution  isof  the  very  best  quality, and  as  a  whole, 
it  deserves  and  will  receive  from  the  profession,  a 
liberal  patronage. — The  Ohio  Medical  and  Surgical 
Journal. 

The  author  has  evidently  ransacked  every  stand- 
ard treatiseof  ancient  and  modern  times,  and  all  that 
is  really  practically  useful  at  the  bedside  will  be 
found  in  a  form  at  once  clear,  distinct,  and  interest- 
ing.— Edinburgh  Monthly  Medical  Journal. 

Druitt's  work,  condensed,  systematm,  lucid,  and 
practical  as  it  is,  beyond  most  works  on  Surgery 


accessible  to  the  American  student,  has  had  much 
currency  in  this  country,  and  under  its  present  au- 
spices promises  to  rise  to  yet  higher  favor,  ihe  il- 
lustrations of  the  volume  are  good,  and.  in  a  word, 
the  publishers  have  acquitted  themselves  fully  of 
their  duty. — The  Western  Journal  of  Medicine  and 
Surgery. 

The  most  accurate  and  ample  resumfe  of  the  pre- 
sent state  of  Surgery  that  we  are  acquainted  with — 
Dublin  Medical  Journal. 

A  belter  book  on  the  principles  and  practice  of 
Surgery  as  now  understood  in  England  and  America, 
has  not  been  given  to  the  profession.— J5 osion  Medi- 
cal and  Surgical  Journal, 

An  unsurpassable  compendium,  not  only  of  Sur- 
gical, but  of  Medical  Practice. — London  Medical 
Gazette. 

This  w^ork  merits  our  warmest  commendations, 
and  we  strongly  recommend  it  to  young  surgeons  as 
an  admirable  digest  of  the  principles  and  practice  of 
modern  Surgery. — Medical  Gazette. 

It  may  be  said  with  truth  that  the  work  of  Mr. 
Druitt  affords  a  complete,  though  brief  and  con- 
j  densed  view,  of  the  entire  field  of  modern  surgery. 
I  We  know  of  no  work  on  the  same  subject  having  the 
1  appearance  of  a  manual,  which  includes  so  many 
topics  of  interest  to  the  surgeon  ;  and  the  terse  man- 
ner in  which  each  has  been  treated  evinces  a  most 
enviable  quality  of  mind  on  the  part  of  the  author, 
who  seems  to  have  an  innate  power  of  searching 
out  and  grasping  the  leading  facts  and  features  of 
the  most  elaborate  productions  of  the  pen.  It  is  a 
useful  handbook  for  the  practitioner,  and  we  should 
deem  a  teacher  of  surgery  unpardonable  who  did  not 
recommend  it  to  his  pupils.  In  our  own  opinion,  it 
is  admirably  adapted  to  the  wants  of  the  student. — 
Provincial  Medical  and  Surgical  Journal. 


DUNGLISON,    FORBES,   TWEEDIE,    AND   CONOLLY. 
THE  CYCLOPEDIA  OF  PRACTICAL  MEDICINE:  comprising  Treatises  on 

the  Nature  and  Treatment  of  Diseases,  Materia  Medica,  and  Therapeutics,  Diseases  of  Women 
and  Children,  Medical  Jurisprudence,  &c.  &c.  In  four  large  super  royal  octavo  volumes,  of 
3254  double-columned  pages,  strongly  and  handsomely  bound. 

*^*  This  work  contains  no  less  than  four  hundred  and  eighteen  distinct  treatises,  contributed  by 
sixty-eight  distinguished  physicians. 

unquestionably  one  of  very  great  value  to  the  prac- 
titioner. This  estimate  of  it  has  not  been  formed 
from  a  hasty  examination,  but  after  an  intimate  ac- 
quaintance derived  from  frequent  consultation  of  it 
during  the  pas't  nine  or  ten  years.  The  editors  are 
practitioners  of  established  reputaticm,  and  the  list 
of  contributors  embraces  many  of  the  most  eminent 
professors  and  teachers  of  London,  Edinburgh,  Dub- 
lin, and  Glasgow.  It  is,  indeed,  the  great  merit  of 
this  work  that  the  principal  articles  have  been  fur- 
nished by  practitioners  who  have  not  only  devoted 
especial  attention  to  the  diseases  about  which  tbey 
have  written,  but  have  also  enjoyed  opportunities 
for  an  extensive  practical  acquaintance  with  them, 
and  whose  reputation  carries  the  assurance  of  their 
competency  justly  to  appreciate  the  opinions  of 
others,  while  it  stamps  their  own  doctrines  with 
high  and  just  authority. — American  Medical  Journ. 


The  most  complete  work  on  Practical  Medicine 
extant;  or,  at  least,  in  our  language.— .Bw^a/o 
Medical  atid  Surgical  Journal. 

For  reference,  it  is  above  all  price  to  every  prac- 
titioner.— Western  Lancet. 

One  of  the  most  valuable  medical  publications  of 
the  day — as  a  work  of  reference  it  is  invaluable. — 
Western  Journal  of  Medicine  and  Surgery. 

It  has  been  to  us,  both  as  learner  and  teacher,  a 
work  for  ready  and  frequent  reference,  one  in  which 
modern  Englisli  medicine  is  exhibited  in  the  most 
advantageous  light. — Medical  Examiner. 

We  rejoice  that  this  work  is  to  be  placed  within 
the  reach  of  the  profession  in  this  country,  it  being 


DUNGLISON    (ROBLEY),    M.D., 

Professor  of  the  Institutes  of  Medicine,  in  the  Jefferson  Medical  College,  Philadelphia. 

HUMAN  HEALTH;  or,  the  Influence  of  Atmosphere  and  Locality,  Change  of 

Air  and  Climate,  Seasons,  Food,  Clothing,  Bathing,  Exercise,  Sleep,  cVc.  &:c  ,  on  Healthy  Man; 
constituting  Elements  of  Hygiene.  Second  edition,  with  many  modifications  and  additions.  In 
one  octavo  volume,  of  464  pages. 


12 


BLANCHARD   &   LEA'S   MEDICAL 


DUNGLISON    (ROBLEY),    M.D., 

Professor  of  Institutes  of  Medicine  in  the  Jefferson  Medical  College,  Philadelphia. 

MEDICAL   LEXICON;   a  Dictionary  of  Medical  Science,  containins:  a  concise 

Explanation  of  the  various  Subjects  and  Terms  of  Physiology,  Pathology,  Hygiene,  Therapeutics, 
Pharmacology,  Obstetrics,  Medical  Jurisprudence,  &c.  With  the  French  and  other  Synonymes ; 
Notices  of  Climate  and  of  celebrated  Mineral  Waters;  Formulse  for  various  Ofiieinal,'Emp'irical, 
and  Dietetic  Preparations,  etc.  Ninth  edition,  revised.  In  one  very  thick  octavo  volume,  of 
over  nine  hundred  large  double-columned  pages,  strongly  bound  in  leather,  M'ith  raised  bands. 
(Just  Issued.) 

Every  successive  edition  of  this  vv^ork  bears  the  marks  of  the  industry  of  the  author,  and  of  his 
determination  to  keep  it  fully  on  a  level  with  the  most  advanced  state  of  medical  science.  Thus 
the  last  two  editions  contained  about  nine  thousand  subjects  and  terms  not  comprised  in  the  one 
immediately  preceding,  and  the  present  has  not  less  than  four  thousand  not  in  any  former  edition. 
As  a  complete  Medical  Dictionary,  therefore,  embracing  over  FIFTY  THOUSAND  DEFINI- 
TIONS, in  all  the  branches  of  the  science,  it  is  presented  as  meriting  a  continuance  of  the  great 
favor  and  popularity  which  have  carried  it,  within  no  very  long  space  of  time,  to  a  ninth  edition. 

Every  precaution  has  been  taken  in  the  preparation  of  the  present  volume,  to  render  its  mecha- 
nical execution  and  typographical  accuracy  worthy  of  its  extended  reputation  and  universal  use. 
The  very  extensive  additions  have  been  accommodated,  without  materially  increasing  the  bulk  of 
the  volurne  by  the  employment  of  a  small  but  exceedingly  clear  type,  cast  for  this  purpose.  The 
press  has  been  watched  with  great  care,  and  every  eHbrt  used  to'insure  the  verbal  accuracy  so  ne- 
cessary to  a  work  of  this  nature.  The  whole  is  printed  on  fine  white  paper  ;  and,  while  thus  exhi- 
biting "in  every  respect  so  great  an  improvement  over  former  issues,  it  is  presented  at  the  original 
exceedingly  low  price. 


A  miracle  of  labor  and  industry  in  one  who  has 
written  able  and  voluminous  works  on  nearly  every 
branch  of  medical  science.  Tiiere  could  be  no  more 
useful  book  to  the  student  or  practitioner,  in  the 
present  advancing  age,  than  one  in  which  would  be 
found,  in  addition  to  the  ordinary  meaning  and  deri- 
vation of  medical  terms — so  many  of  which  are  of 
modern  introduction — concise  descriptions  of  their 
explanation  and  employment;  and  ail  this  and  much 
more  is  contained  in  the  volume  before  us.  It  is 
therefore  almost  as  indispensable  to  the  other  learned 
professions  as  to  our  own.  In  fact,  to  all  who  may 
have  occasion  to  ascertain  the  meaning  of  any  word 
belonging  to  the  many  branches  of  medicine.  From 
a  careful  examination  of  the  present  edition,  we  can 
vouch  for  its  accuracy,  and  for  its  being  brought 
quite  up  to  the  date  of  publication  ;  the  author  states 
in  his  preface  that  he  has  added  to  it  about  four  thou- 
sand terms,  which  are  not  to  be  found  in  the  prece- 
ding one.  —  Dublin  Quarterly  Journal  of  Medical 
Sciences. 

On  the  appearance  of  the  last  edition  of  this 
valuable  work,  we  directed  the  attention  of  our 
readers  to  its  peculiar  merits;  and  we  need  do 
little  more  tiian  state,  in  reference  to  the  present 
reissue,  that,  notwithstanding  the  large  additions 
previously  made  to  it,  no  fewer  than  four  thou- 
eand  terms,  not  to  be  found  in  the  preceding  edi- 
tion, are  contained  in  the  volume  before  us. — 
Whilst  it  is  a  wonderful  monument  of  its  author's 
erudition  and  industry,  it  is  also  a  work  of  great 
practical  utility,  as  we  can  testify  from  our  own 
experience;  for  we  keep  it  constantly  within  our 
reach,  and  make  very  frequent  reference  to  it, 
nearly  always  finding  in  it  the  information  we  seek. 
— British  and  Foreign  Med.-Chirurg.  Review. 

It  has  the  rare  merit  that  it  certainly  has  no  rival 
in  the  English  language  for  accuracy  and  extent 
of  references.  The  terms  generally  include  sliort 
physiological  and  pathological  descriptions,  so  that, 
as  the  author  justly  observes,  the  reader  does  not 
possess  in  this  work  a  mere  dicti(mary,  but  a  book, 
which,  while  it  instructs  him  in  medical  etymo- 
logy, furnishes  him  with  a  large  amount  of  useful 
informati<m.  The  author's  labors  have  been  pro- 
perly appreciated  by  his  own  countrymen  ;  and  we 


can  only  confirm  their  judgment,  by  recommending 
this  most  useful  volume  to  the  notice  of  our  cisat- 
lantic readers.  No  medical  library  will  be  complete 
without  it. — London  Med.  Gazette. 

It  is  certainly  more  complete  and  compreliensive 
than  any  with  which  we  are  acquainted  in  the 
English  language.  Few,  in  fact,  could  be  found 
belter  qualified  than  Dr.  Dunglison  for  the  produc- 
tion of  such  a  work.  Learned,  industrious,  per- 
severing, and  accurate,  he  brings  to  the  task  all 
the  peculiar  talents  necessary  for  its  successful 
performance;  while,  at  tiie  same  time,  his  fami- 
liarity with  the  writings  of  the  ancient  and  modern 
"masters  of  our  art,"  renders  him  skilful  to  note 
the  exact  usage  of  the  several  term.s  of  science, 
and  the  various  modifications  which  medical  term- 
inology has  undergone  with  the  change  of  theo- 
ries or  the  progress  of  improvement.  —  American 
Journal  of  the  Medical  Sciences. 

One  of  the  most  complete  and  copious  known  to 
the  cultivators  of  medical  science. — Boston  Med. 
Journal. 

A  most  complete  Medical  Lexicon — certainly  one 
of  the  best  works  of  the  kind  in  the  language. — 
Charleston  Medical  Journal. 

The  most   complete  Medical   Dictionary   in  the 
j  English  language. —  Western  Lancet. 

I  It  has  not  its  superior,  if  indeed  its  equal,  in  the 
English  language. — St.  Louis  Medical  and  Surgical 
Journal. 

Familiar  with  nearly  all  the  medical  dictiona- 
ries now  in  print,  we  consider  the  one  before  us 
the  most  comj)lete,  and  an  indispensable  adjunct  to 
every  medical  library. — British  American  Medical 
Journal. 

We  repeat  our  declaration,  that  this  is  the  best 
Medical  Dictionary  in  the  language. — West.  Lancet. 

The  very  best  Medical  Dictionary  now  extant. — 
Southern  Medical  and  Surgical  Journal. 

The  most  comprehensive  and  best  English  Dic- 
tionary of  medical  terms  extant. — Buffalo  Medical 
Journal. 


•  BY   the   same   author. 

THE  PRACTICE  OF  MEDICINE.     A  Treatise  on  Special  Pathology  and  The 


rapeutics.     Third  Edition. 


Upon  every  topic  embraced  in  the  work  the  latest 

information  will   be  found  carefully  posted  up. 

Medical  Examiner. 

The  student  of  medicine  will  find,  in  these  two 
elegant  volumes,  a  mine  of  facts,  a  gathering  of 
precepts  and  advice  from  the  world  of  experience, 
that  will  nerve  him  with  courage,  and  faithfully 
direct  him  in  his  efforts  to  relieve  the  physical  suf- 


In  two  large  octavo  volumes,  of  fifteen  hundred  pages. 

Boston  Medical  and  Surgical 


ferings  of  the  race.- 
Journal. 

It  is  certainly  the  most  complete  treatise  of  which 
we  have  any  knowledge. —  Wester7i  Jotcrnal  of  Medi- 
cine aiid  Surgery. 

One  of  the  most  elaborate  treatises  of  the  kind 
we  have. — Southern  Med.  and  Surg.  Journal. 


AND    SCIENTIFIC    PUBLICATIONS. 


13 


DUNGLISON    (ROBLEY),    M.D., 

Professor  of  Institutes  of  Medicine  in  the  Jefferson  Medical  College,  Philadelphia. 

HUMAN    PHYSIOLOGY.     Seventh   edition.     Thoroughly  revised    and  exten- 


In  two  large  and  hand- 


sively  modified  and  enlarged,  with  nearly  five  hundred  illustrations, 
gomely  printed  octavo  volumes,  containing  nearly  1450  pages. 

On  no  previous  revision  of  this  work  has  the  author  bestowed  more  care  than  on  the  present, 
it  having  been  subjected  to  an  entire  scrutiny,  not  only  as  regards  the  important  maiieis  of 
which  it  treats,  but  also  the  language  in  which  they  are  conveyed ;  and  on  no  former  occasion 
has  he  felt  as  satisfied  with  his  endeavors  to  have  the  work  oa  a  level  with  the  existing  state  of 
the  science. 

The  increased  amount  of  matter  may  be  estimated  from  the  fact  that  the  mere  list  of  authors 
referred  to  in  the  preparation  of  the  additions  to  this  edition  alone  extends  over  nine  large 
and  closely  printed  pages.  The  number  of  illustrations  has  been  greatly  extended,  the  present 
edition  containing  four  hundred  and  seventy-four,  while  the  last  had  but  three  hundred  and  sixty- 
eight;  while,  in  addition  to  this,  many  new  and  superior  wood-cuts  have  been  substituted  for  those 
which  were  not  deemed  sufficiently  accurate  or  satisfactory.  The  mechanical  execution  of  the 
work  has  also  been  improved  in  every  respect,  and  the  whole  is  confidently  presented  as  worthy 
the  great  and  continued  favor  which  it  has  so  long  received  from  the  profession. 


It  has  long  since  taken  rank  as  one  of  the  medi- 
cal classics  of  our  language.  To  say  that  it  is  by 
far  the  best  text-book  of  physiology  ever  published 
in  this  country,  is  but  echoing  the  general  testi- 
mony of  the  profession. — N.  Y.  Journal  of  Medicine. 

There  is  no  single  book  we  would  recommend  to 
the  student  or  physician,  with  greater  confidence 
than  the  present,  because  in  it,  will  be  found  a  mir-, 
rorof  almost  every  standard  pliysiological  work  of 
the  day.  We  most  cordially  recommend  the  work 
to  every  member  of  the  profession,  and  no  student 
should  be  without  it,    It  is  the  completest  work  on 


Physiology  in  the  English  language,  and  is  highly 
creditable'td  the  author  and  publishers. — From  the 
Canadian  Medical  Journal. 

The  most  conjplete  and  satisfactory  system  of 
Physiology  in  the  English  language. — Amer.  Med. 
Journal . 

The  best  work  of  the  kind  in  the  English  lan- 
guage.— Silliman's  Journal. 

The  most  full  and  complete  system  of  Pliysiology 
in  our  language. — Western  Lancet. 


BY   THE   SAME   AUTHOR. 

GENERAL    THERAPEUTICS    AND    MATERIA  MEDIC  A;   adapted  for  a 

Medical  Text-book.     Fourth  edition,  much  improved.     With  one  hundred  and  eighty-two  illus- 
trations.   La  two  large  and  handsomely  prmted  octavo  volumes,  of  1000  pages. 


In  this  work  of  Dr.  Dunglison,we  recognize  the  I 
same  untiring  industry  in  the  collection   and  em- 
bodying of  facts  on  the  several  subjects  of  which  he 
treats,  that   has  heretofore  distinguished  him,  and  | 
we  cheerfully  point  to  these  volumes,  as  two  of  the  | 
most  interesting  that  we  know  of.     In  noticing  tlie 
additions  to  this,  the  fourth  edition,  there  is  very 
little  in  the  periodical  or  annual   literature  of  the 
profession,   published    in   the    interval   which    has 
elapsed  since  the  issue  of  the  first,  that  has  escaped 
the  caret'ul   search  of  the  author.     As  a  book  for 
reference,  it  is  invaluable. — Charleston  Med.  Jour 
nal  and  Review. 

It  may  be  said  to  be  the  work  now  upon  the  sub- 
jects upon  which  it  treats. —  Western  Lancet. 


As  a  text-book  for  students,  for  whom  it  is  par- 
ticularly designed,  we  know  of  none  superior  to 
it. — St.'Louis  Medical  and  Surgical  Journal. 

It  purports  to  be  a  new  edition,  but  it  is  rather 
a  new  book,  so  greatly  has  it  been  improved,  both 
in  the  amount  and  quality  of  the  matter  which  it 
contains. — N.  O.  Medical  and  Surgical  Journal. 

We  bespeak  for  this  edition,  trom  the  profession, 
an  increase  of  patronage  over  any  of  its  former 
ones,  on  account  of  its  increased  merit.  —  N.  Y. 
Journal  of  Medicine. 

We  consider  this  work  unequalled. — Boston  Med. 
and  Surg.  Journal. 


BY   THE   SAME    AUTHOR. 

NEW  REMEDIES,  WITH  PORMUL.^  FOR  THEIR  ADMINISTRATION. 

Sixth  edition,  with  extensive  Additions.     In  one  very  large  octavo  volume,  of  over  750  pages. 

diseases  and  for  remedies,  will  be  found  greatly  to 
enhance  its  value. — New  York  Med.  Gazette. 

The  great  learning  of  the  author,  and  his  remark- 
able industry  in  pushing  his  researches  into  every 
source  whence  information  is  derivable,  has  enabled 
him  to  throw  together  an  extensive  mass  of  facts 
and  statements,  accompanied  by  full  reference  to 
authorities;  which  last  feature  renders  the  work 
practically  valuable  to  investigators  who  desire  to 
examine  the  original  papers.— TAe  American  Journal 
of  Pharmacy. 


One  of  the  most  useful  of  the  author's  works. — 
Southern  Medical  and  Surgical  Jotcriial. 

This  well-known  and  standard  book  has  now 
reached  its  sixth  edition,  and  has  been  enlarged  and 
improved  by  the  introduction  of  all  the  recent  gifts 
to  therapeutics  which  the  last  few  years  have  so 
richly  produced,  including  the  anaisthetic  agents, 
&c.  This  elaborate  and  useful  volume  should  be 
found  in  every  medical  library,  for  as  a  book  of  re- 
ference, for  physicians,  it  is  unsurpassed  by  any 
other  work  in  existence,  and  the  double  index  for 


DUFTON    (WILLIAM),    M.R.C.S.,    &.C. 
THE   NATURE   AND   TREATMENT    OF   DEAFNESS   AND  DISEASES 

OF  THE  EAR  :  and  the  Treatment  of  the  Deaf  and  Dumb,    One  small  12mo.  vol.    pp.  120. 


14 


BLANCHARD   &   LEA'S   MEDICAL 


DE  JONGH  (L.  J.),  M.  D.,  &,c. 
THE  THREE  KINDS   OF  COD-LIVER  OIL,  comparatively  considered,  with 

their  Chemical  and  Therapenlic  Properties.  Translated,  with  an  Appendix  and  Cases,  by 
Edward  Carey,  JN'I  D.  To  which  is  added  an  article  on  the  subject  from  "  Dunglison  on  New 
Remedies."     In  one  small  12mo.  volume,  extra  cloth. 


A   TREATISE    ON 


DURLACHER    (LEWIS! 
CORNS,   BUNIONS,   THE 


DISEASES    OF    NAILS, 


AND  THE  GENERAL  MANAGEMENT  OF  THE  FEET, 
pp.  134. 


In  one  12mo.  volume,  cloth. 


DAY  (GEORGE  EJ,  M.  D. 
A  PRACTICAL  TREATISE  ON  THE  D03IESTIC  MANAGEMENT  AND 

MORE  IMPORTANT  DISEASES  OF  ADVANCED  LIFE.  With  an  Appendix  on  a  new 
and  successful  mode  of  treating-  Lumbago  and  other  forms  of  Chronic  Rheumatism.  One  volume, 
octavo,  226  pages. 


ELLIS  (BENJAMIN;,  M.  D. 
THE    MEDICAL   FORMULARY :   being  a  Collection  of  Prescriptions,  derived 

from  the  writings  and  practice  of  many  of  the  most  eminent  physicians  of  America  and  Europe. 
To  which  is  added  an  Appendix,  containing  the  usual  Dietetic  Preparations  and  Antidotes  for 
Poisons.  The  whole  accompanied  with  a  few  brief  Pharmaceutic  and  Medical  Observations. 
Ninth  edition,  corrected  and  extended,  by  Samuel  George  Morton,  M.  D.  In  one  neat  octavo 
volume,  of  two  hundred  and  sixty-eight  pages. 


FERGUSSON   (WILLIAM),  F.  R.  S., 

Professor  of  Surgery  in  King's   College,  London,  &c. 

A  SYSTEM  OF  PRACTICAL  SURGERY.  Fourth  American,  from  the  third 
and  enlarged  London  edition.  In  one  large  and  beautifully  printed  octavo  volume,  of  about  seven 
hundred  pages,  with  three  hundred  and  ninety-three  handsome  illustrations.     {Now  Ready.) 


The  most  important  subjects  in  connection  with 
practical  surgery  which  have  been  more  recently 
brought  under  the  notice  of,  and  discussed  by,  the 
surgeons  of  Great  Britain,  are  fully  and  dispassion- 
ately considered  by  Mr.  Fergusson,  and  that  which 
was  before  ■wanting  has  now  been  supplied,  so  that 
we  can  now  look  upon  it  as  a  work  on  practical  sur- 
gery instead  of  one  on  operative  surgery  alone, 
which  many  have  hitherto  considered  it  to  be;  And 
Ave  think  the  author  has  shown  a  wise  discretion  in 
making  the  additions  on  surgical  disease  which  are 
to  be  found  in  the  present  volume,  and  has  very 
much  enhanced  its  value;  for,  besides  two  elaborate 
chapters  on  the  diseases  of  bones  and  joints,  which 
■were  wanting  before  he  has  headed  each  chief  sec- 
tion of  the  work  by  a  general  description  of  the  sur- 
gical disease  and  injury  of  that  region  of  the  body 
which  is  treated  of  in  each,  prior  to  entering  into  the 
consideration  of  the  more  special  morbid  conditions 
and  their  treatment.  There  is  also,  as  in  former 
editions,  a  sketch  of  the  anatomy  of  particular  re- 
gions. We  have  now  pointed  out  some  of  the  prin- 
cipal additions  in  this  work.  There  was  some 
ground  formerly  for  the  complaint  before  alluded  to, 
that  it  dwelt  too  exclusively  on  operative  surgery  ; 
but  this  defect  is  now  removed,  and  the  book  is  more 
than  ever  adapted  for  the  purposes  of  the  practitioner, 
whelher  he  confines  himself  more  strictly  to  the 
operative  department,  or  follows  surgery  on  a  more 
comprehensive  scale.— ilferfica/  Times  and  Gazette. 

No  work  was  ever  written  which  more  nearly 
comprehended  the  necessities  of  the  student  and 
practitioner,  and  was  more  carefully  arranged  to 
that  singlepurpose  than  this.— A^.  Y.  Med.  and  Surg. 
Journal. 


The  addition  of  many  new  pages  makes  this  work 
more  tnanever  indispensable  to  the  student  and  prac- 
titioner.— RanJcing^s  Abstract,  January,  1S53. 

For  the  general  practitioner,  M''ho  does  not  make 
a  specialty  of  surgery,  it  is  certainly  invaluable. 
The  style  is  concise,  pointed,  and  clear.  The  de- 
scriptions of  the  various  operations^are  concentrated 
and  accurate,  so  that  in  cases  of'  emergency,  the 
principles  of  the  most  difficult  operations  may  be 
obtained  by  a  reference  of  a  few  moments  to  its 
pages. — Western  Lancet. 

As  a  book  of  reference  for  the  surgeon  and  student 
it  is  an  admirable  work,  purely  on  the  practice  of 
surgery,  and  not  encumbered  with  any  irrelevant 
matter,  nor  with  too  much  theory  or  discussion  on 
surgical  subjects. — Stethoscoi^e. 

Among  the  numerous  works  upon  surgery  pub- 
lished of  late  years,  we  know  of  none  we  value 
more  highly  than  the  one  before  us.  It  is  perhaps 
the  very  best  we  have  for  a  text-book  and  for  ordi- 
nary reference,  being  concise  and  eminently  practi- 
cal.— Southern  Med.  and  burg.  Journal. 

The  nature  and  variety  of  these  additions,  how- 
ever, must  render  it  of  course  impracticable  to  dwell 
upon  them  here;  and  the  best  we  can  do  for  the 
book  itself,  as  well  as  for  our  readers,  is  to  recom- 
mend all  who  desire  one  of  the  most  instructive 
manuals  of  practical  surgery,  to  provide  tliemselves 
with  copies  for  their  private  reading. — Medical 
Examiner. 


FRICK  (CHARLES),  M.  D. 

RENAL    AFFECTIONS;    their  Diagnosis  and  Pathology. 
One  volume,  royal  12mo.,  extra  cloth. 


With  illustrations. 


GUTHRIE  (G.  J.),   F.  R. 


S.,  &.C. 
THE  ANATOMY  OF  THE   BLADDER  AND  URETHRA,  and  the  Treat- 

ment  of  the  Ob:^l^uctions  to  which  those  Passages  are  liable.     In  one  volume,  octavo,  150  pages. 


AND    SCIENTIFIC    PUBLICATIONS. 


15 


FOWNES  (GEORGE),   PH.  D.,  &,c. 
ELEMENTARY    CHEMISTRY;    Theoretical  and  Practical.     With  numerous 

illustrations  Third  American,  from  a  late  London  edition.  Edited,  with  Additions,  by  Robert 
Bridges,  M.  D.  In  one  large  royal  12mo.  v'olume,  of  over  500  pages,  with  about  180  wood-cuts, 
sheep,  or  extra  cloth. 

The  work  of  Dr.  Fownes  has  lonof  been  before  j  and  facts  of  modern  chemistry,  oricrinally  intended 
the  public,  and  its  merits  have  been  fully  appreci-  \  as  a  guide  to  the  lectures  of  the  author,  corrected  by 
ated  as  the  best  text-book  on  chemistry  now  in  j  his  own  hand  shortly  before  his  death  in  1849,  and 
jexistence.    We  do  not,  of  course,  place  it  in  a  rank  |  recently  revised  by  Dr.  Bence  Jones,  who  has  made 

some  additions  to  the  chapter  on  anima!  chemistry. 
Although  not  intended  to  supersede  the  more  extended 
treatises  on  chemistry,  Professor  Fownes's  Manual 


superior  to  the  works  of  Brande,  Graham,  Turner, 
Gregory,  or  Gmelin,  but  we  say  that,  as  a  work 
for  students,  it  is  preferable  to  any  of  them. — Loti- 
clon  Journal  of  Medicine. 

The  rapid  sale  of  this  Manual  evinces  its  adapta- 
tion to  the  -wants  of  the  student  of  chemistry'.  Avhilst 
the  well-known  merits  of  its  lamented  author  have 
constituted  a  guarantee  for  its  value,  as  a  faithful 
exposition  of  the  general  principles  and  most  im- 
portant facts  of  the  science  to  which  it  professes  to 
be  an  introduction. — British  and  Foreign  Medico- 
Chirurgical  Review. 

A  work  well  adapted  to  the  wants  of  the  student. 
It  is  an  excellent  exposition  of  the  chief  doctrines 


may,  %ve  think,  be  ot'ten  used  as  a  work  of  reference, 
even  by  those  advanced  in  the  study,  who  may  be  de- 
sirous of  refreshing  their  memory  on  some  forgotteu 
point.  The  size  of  the  work,  and  still  more  the  coa- 
densed  yet  perspicuous  style  in  which  it  is  written, 
absolve  it  from  the  charges  very  properly  urged 
against  most  manuals  termed  popular,  viz.:  of  omit- 
ting details  of  indispensable  importance,  of  avoiding 
technical  difficulties,  instead  of  explaining  them, 
and  of  treating  subjects  of  high  scientific  interest 
in  an  unscientific  way. — Edinburgh  Monthly  Jour- 
nal of  Melical  Science. 


GRAHAM   (THOMAS),    F.R.S,, 

Professor  of  Chemistry  in  University  College,  London,  &;c 

THE  ELEMENTS  OF  CHEMISTRY.     Including  the  application  of  the  Science 
to  the  Arts.    With  numerous  illustrations.    With  Notes  and  Additions,  by  Robert  Bridges, 
M.  D.,  &c.  &c.     Second  American,  from  the  second  and  enlarged  London  edition 
PART  I.  {Lately  Issued)  large  8vo.,  430  pages,  185  illustrations, 
PART  II.  {Preparing)  to  match. 

The  great  changes  which  the 'Science  of  chemistry  has  undergone  within  the  last  few  years,  ren- 
der a  new  edition  of  a  treatise  like  the  present,  almost  a  new  work.  The  author  has  devoted 
several  years  to  the  revision  of  his  treatise,  and  has  endeavored  to  embody  in  it  every  fact  and 
inference  of  importance  which  has  been  observed  and  recorded  by  the  great  body  of  chemical 
investigators  who  are  so  rapidly  changing  the  face  of  the  science.  In  this  manner  the  work  has 
been  greatly  increased  in  size,  and  the  number  of  illustrations  doubled  ;  while  the  labors  of  the  editor 
have  been  directed  towards  the  introduction  of  such  matters  as  have  escaped  the  attention  of  the 
author,  or  as  have  arisen  since  the  publication  of  the  first  portion  of  this  edition  in  London,  in  IS^O. 
Printed  in  handsome  style,  and  at  a  very  low  price,  it  is  therefore  confidently  presented  to  the  pro- 
fession and  the  student  as  a  very  complete  and  thorough  text-book  of  this  important  subjects 


GROSS  (SAMUEL  D.),   M.  D., 

Professor  of  Surgery  in  the  Louisville  Medical  Institute,  &c." 

A  PRACTICAL  TREATISE  ON  THE  DISEASES   AND   INJURIES   OF 

THE  URINARY  ORGANS.     In  one  large  and  beautifully  printed  octavo  volume,  of  over  seven 
hundred  pages.     With  numerous  illustrations. 

A  volume  replete  with  truths  and  principles  of  the 
utmost  value  in  the  investigation  of  these  diseases. — 
American  Medical  Journal. 

Dr.  Grnss  has  brought  all  his  learning,  experi- 
ence, tact,  and  judgment  to  the  task,  and  has  pro- 
duced a  work  worthy  of  his  high  reputation.  We 
feel  perfectly  safe  in  recommending  it  to  our  read- 
ers as  a  monograph  unequalled  in  interest  and 
practical  value  by  any  other  on  the  subject  in  our 
language;  and  we  cannot  help  saying,  that  we  es- 
teem it  a  matter  of  just  pride,  that  another  work 
so  creditable  to  our  country  has  been  contributed 
to  our  medical  literature  by  a  Western  physician. 
— The  Western  Journal  of  Medicine  and  Surgery. 

AVe  regret  that  our  limits  preclude  such  a  notice 
as  this  valuable  contribution  to  our  American 
Medical  Literature  merits.  We  have  only  room 
to  say  that  the  author  deserves  the  thanks  of  the 
profession  for  this  elaborate  production;  which 
cannot  fail  to  augment  the  exalted  reputation  ac- 
quired by  his  former  works,  for  whicli  he  has  been 
honored  at  home  and  abroad. — N.  Y.  Med  Gazette. 


Whoever  will  peruse  the  vast  amount  of  valuable 
practical  information  it  contains,  and  which  we 
have  been  unable  even  to  notice,  will,  we  think, 
agree  with  us,  that  there  is  no  work  in  the  English 
language  which  can  make  any  just  pretensions  to 

be  its  equal.     Secure  in  the  esteem  and  ctmfidence    v-. ....... ^..«o.. . v...  ..j , 

of  the  profession  in  this  country,  at  least,  its  distin-  I  and  Foreign  Medico-Chirurgical  Revietv 


guished  author  will  doubtless  receive  their  warmest 
ccmgratulations  that  he  has  succeeded  in  producing 
a  treatise  so  creditable  to  himself,  and,  as  we  hum- 
bly believe,  to  American  surgical  literature. — N.  Y. 
Journal  of  Medicine. 

It  has  remained  for  an  American  writer  to  wipe 
away  this  reproach  ;  and  so  completely  has  the  task 
been  fulfilled,  that  we  venture  to  predict  for  Dr. 
Gross's  treatise  a  permanent  place  in  the  literature 
of  surgery,  worthy  to  rank  with  the  best  works  of 
the  present  age.  Not  merely  is  the  matter  good, 
but  the  getting  up  of  the  volume  is  most  creditable 
to  transatlantic  enterprise;  the  paper  and  print 
would  do  credit  to  a  first-rate  London  establishment ; 
and  the  numerous  wood-cuts  which  illustrate  it,  de- 
monstrate that  America  is  making  rapid  advances  in 
this  department  of  art.  We  have,  indeed,  unfeigned 
pleasure  in  congratulating  all  concerned  in  this  pub- 
lication, on  the  result  of  their  labours;  and  expe- 
rience a  feeling  something  like  what  animates  a  long- 
expectant  husbandman,  Avho,  often  times  disappointed 
by  the  produce  of  a  favorite  field,  is  at  last  agree- 
ably surprised  by  a  stately  crop  which  may  bear 
comparison  with  any  of  its  former  rivals.  The 
grounds  of  our  higli  appreciation  of  the  work  will 
be  obvious  as  we  proceed;  and  we  doubt  not  that 
the  present  facilities  for  obtaining  American  books 
will  induce  many  of  our  readers  to  verify  our  re- 
commendation by  their  own  perusal  of  it. — British 


GRIFFITH  (JOHN   WILLIAM),   M.  D.,  &.C. 
A  PRACTICAL    MANUAL   ON  THE   BLOOD   AND   SECRETIONS  OF 

THE  HUMAN  BODY.    Royal  12mo.,  with  plates.    (See  "  Manuals  on  Blood  and  Urine.") 


16 


BLANCHARD    &    LEA'S    MEDICAL 


GLUGE  (GOTTLIEB),  M.  D., 

Professor  of  Physiology  and  Pathological  Anatomy  in  the  University  of  Brussels,  &c. 

AN  ATLAS   OF   PATHOLOGICAL   HISTOLOGY.     Translated,  with  Notes 

and  Additions,  by  Joseph  Leidy,  M.  D.,  Professor  of  Anatomy  in  the  University  of  Pennsylva- 
nia. In  one  volume,  v«ry  large  imperial  quarto,  with  three  hundred  and  twenty  figures,  plain 
and  colored,  on  twelve  copperplates. 


We  are  glad  to  see  this  excellent  work  of  Gluge 
translated  into  English  by  so  competent  a  hand,  and 
put  within  the  reach  of  the  profession  in  this  coun- 
try. The  history  of  the  development  and  changes  of 
the  elements  of  pathological  tissues,  has  become 
now  a  necessary  introduction  to  the  study  of  morliid 
anatomy.  1 1  can  no  longer  be  looked  upon  as  merely 
accessory.  Bearing  the  same  relation  to  it  as  does 
normal  histology  to  normal  anatomy,  it  appears  to 
us  to  be  of  still  higher  importance,  since  it  has  a 
closer  and  more  direct  bearin"^  upon  practical  medi- 
cine. Whatever  makes  our  knowledge  of  diseased 
structure  clearer,  must  throw  light  also  upon  the 
plan  of  cure,  and  show  us,  too,  in  many  instances, 
where  a  cure  is  impossible.  This  being,  as  far  as 
we  know,  the  only  work  in  which  pathological  his- 
tology is  separately  treated  of  in  a  comprehensive 
manner,  it  will,  we  think,  for  this  reason,  be  of  infi- 


nite service  to  those  who  desire  to  investigate  the 
subject  systematically,  and  who  have  felt  the  diffi- 
culty of  arranging  in  their  mind  the  unconnected 
observations  of  a  great  number  of  authors.  The 
development  of  the  morbid  tissues,  and  the  formation 
of  abnormal  products,  may  now  be  followed  and 
studied  with  the  same  ease  and  satisfaction  as  the 
best  arranged  system  of  physiology.  —  Ameriean 
Med.  Journal. 

Professor  Gluge's  work  will  be  found  a  very  valu- 
able addition  to  the  micrologist's  collection.  It 
contains,  in  the  compass  of  one  volume,  a  concise 
description  and  well-executed  illustrations  of  the 
elements  to  be  observed  under  the  microscope  in  the 
principal  pathological  lesions. — Dublin  Quarterly 
Journal  of  Medical  Science. 


GRIFFITH  (ROBERT   E.),   M.  D.,  &.c. 

A  UNIVERSAL  FORMULARY,  containing  the  methods  of  Preparintr  and  Ad- 
ministering Officinal  and  other  Medicines.  The  whole  adapted  to  Physicians  and  Pharmaceu- 
tists.    In  one  large  octavo  volume,  of  568  pages,  double  columns. 


Dr.  Griffith's  Formulary  is  worthy  of  recommen- 
dation, not  only  on  account  of  the  care  which  has 
been  bestowed  on  it  by  its  estimable  author,  but  for 
its  general  accuracy,  and  the  richness  of  its  details. 
— Medical  Examiner. 

Most  cordially  Ave  recommend  this  Universal 
Formulary,  not  forgetting  its  adaptation  to  drug- 
gists and  apothecaries,  who  would  find  themselves 
vastly  improved  by  a  familiar  acquaintance  with 
this  every-day  book  of  medicine. — The  Boston  Med. 
and  Surg.  Journal. 

A  very  useful  work,  and  a  most  complete  compen- 
dium on  the  subjectof  materia  medica.  We  know 
<»f  no  work  in  our  lang'uage,  or  any  other,  so  com- 
prehensive in  all  its  details. — London  Lancet. 


Pre-eminent  among  the  best  and  most  useful  com- 
pilations of  the  present  day  will  be  found  the  Avork 
before  us,  which  can  have  been  produced  only  at  a 
very  great  cost  of  thought  and  labor.  A  short  de- 
scription will  suffice  to  show  that  we  do  not  put 
too  high  an  estimate  on  this  work.  We  are  not  cog- 
nizant of  the  existence  of  a  parallel  work.  Its  value 
will  be  apparent  to  our  readers  from  the  sketch  of 
its  contents  above  given.  We  strongly  recommend 
it  to  all  who  are  engaged  either  in  practical  medi- 
cine, or  more  exclusively  with  its  literature. — Lond. 
Med.  Gazette. 

A  valuable  acquisition  to  the  medical  practitioner, 
and  a  useful  book  of  reference  to  the  apothecary  on 
numerous  occasions. — Amer.  Journal  of  Pharmacy. 


BY   THE   SAME   AUTHOR, 


MEDICAL  BOTANY;  or,  a  Description  of  all  the  more  important  Plants  used 
in  Medicine,  and  of  their  Properties,  Uses,  and  Modes  of  Administration.  In  one  large  octavo 
volume,  of  704  pages,  handsomely  printed,  with  nearly  350  illustrations  on  wood. 


One  of  the  greatest  acquisitions  to  American  medi- 
cal literature.  It  should  by  all  means  be  introduced, 
at  the  very  earliest  period,  into  our  medical  schools, 
and  occupy  a  place  in  the  library  of  every  physician 
in  the  land. — South-western  Medical  Advocate. 

Admirably  calculated  for  the  physician  and  stu- 
dent —  we  have  seen  no  work  which  promises 
greater  advantages  to  the  profession.— iV.  0.  Med. 
and  Surg.  Journal. 


One  of  the  few  books  which  supply  a  positive  de- 
ficiency in  our  medical  literature. — Western  Lancet. 

We  hope  the  day  is  not  distant  when  this  work 
will  not  only  be  a  text-book  in  every  medicnl  school 
and  college  in  the  Union,  but  find  a  place  in  the  li- 
brary of  every  private  practitioner. — N.  Y.  Journal 
of  Medicine. 


GREGORY  (WILLIAM),   F.  R.  S.  E., 

Professor  of  Chemistry  in  the  University  of  Edinburgh,  &c. 

LETTERS    TO  A  CANDID    INQUIRER    ON    ANIMAL    MAGNETISM. 

Description  and  Analysis  of  the  Phenomena.     Details  of  Facts  and  Cases.     In  one  neat  volume, 
royal  12mo.,  extra  cloth. 


GARDNER  (D.  PEREIRA),  M.  D. 

MEDICAL  CHExMISTRY,  for  the  use  of  Students  and  the  Profession:  being  a 
Manual  of  the  Science,  with  its  Applications  to  Toxicology,  Physiology,  Tlierapeutics,  Hygiene, 
&c.    In  one  handsome  royal  12mo.  volume,  with  illustrations. 


AND    SCIENTIFIC    PUBLICATIONS.  17 

HASSE  (C.  E.),   M.  D. 
AN  ANATOMICAL  DESCRIPTION  OF  THE  DISEASES  OF  EESPIRA- 

TION  AND  CIRCULATION.     Translated  and  Edited  by  Swaine.    In  one  volume,  octavo. 


HARRISON  (JOHN),   M.  D. 
AN   ESSAY  TOWARDS  A  CORRECT  THEORY  OF  THE  NERVOUS 

SYSTEM.    In  one  octavo  volume,  292  pages. 


HUNTER  (JOHN). 
TREATISE  ON  THE   VENEREAL   DISEASE.     With  Notes  and  numerous 

Additions,  by  Dr.  Ph.  Ricord,  Surgeon  to  the  Venereal  Hospital  of  Paris.  Translated  from  the 
French,  with  additional  Notes,  by  F.  J.  Bumstead,  M.  D.  In  one  octavo  volume,  wiih  plates. 
{Nearly  Ready.) 

Ricord's  Annotations  to  Hunter's  Treatise  are  very  extensive,  amounting  to  nearly  half  as  much 
as  the  original  work,  and  bringing  it  thoroughly  up  to  the  present  state  of  the  subject. 


HORNER  (WILLIAM  E.),  M.  D., 

Professor  of  Anatomy  in  the  University  of  Pennsylvania. 

SPECIAL    ANATOMY    AND    HISTOLOGY.     Eighth  edition.     Extensively 

revised  and  modified.     In  two  large  octavo  volumes,  of  more  than  one  thousand  pages,  hand- 
somely pr/nted,  with  over  three  hundred  illustrations. 

This  work  has  enjoyed  a  thorough  and  laborious  revision  on  the  part  of  the  author,  with  the 
view  of  bringing  it  fully  up  to  the  existing  state  of  knowledge  on  the  subject  of  general  and  special 
anatomy.  To  adapt  it  more  perfectly  to  the  wants  of  the  student,  he  has  introduced  a  large  number 
of  additional  wood-engravings,  illustrative  of  the  objects  described,  while  the  publishers  have  en- 
deavored to  render  the  mechanical  execution  of  the  work  worthy  of  the  extended  reputation  which 
it  has  acquired.  The  demand  which  has  carried  it  to  an  EIGFITH  EDITION  is  a  sulTicient  evi- 
dence of  the  value  of  the  work,  and  of  its  adaptation  to  the  wants  of  the  student  and  professional 
reader. 


HORNER  (W.   E.)  "I  connection  m«A  H.    H.   SMITH. 

ANATOMICAL  ATLAS.     One  volume,  imperial  8vo.     (See  SxMITH.) 


HOBLYN  (RICHARD  D.),  A.  M. 
A  DICTIONARY  OF   THE   TERMS  USED  IN  MEDICINE   AND   THE 

COLLATERAL  SCIENCES.  Revised,  with  numerous  Additions,  from  the  second  London 
edition,  by  Isaac  Hays,  M.  D.,  &c.  In  one  large  royal  12mo.  volume,  of  four  hundred  and  two 
pages,  double  columns. 

We  cannot  too  strongrly  recommend  this  small  and  cheap  volume  to  the  library  of  every  student  and 
practitioner. — Medico-Chirurgical  Review. 


HOPE  (J.),   M.  D.,  F.  R.  S.,  8ic. 
A  TREATISE  ON  THE    DISEASES    OF    THE    HEART    AND   GREAT 

VESSELS.    Edited  by  Pennock.    In  one  volume,  octavo,  with  plates,  572  pages. 


HERSCHEL   (SIR   JOHN    F.  W.),  F.  R.  S.,  &.c. 

OUTLINES  OF  ASTRONOMY.     New  American,  from  the  third  London  edition. 
In  one  neat  volume,  crown  octavo,  with  six  plates  and  numerous  wood-cuts.     {Just  Issued.) 


JOHNSTON  (ALEXANDER  KEITH),  F.  R.  S.,  &c. 
THE  PHYSICAL  ATLAS  OF  NATURAL   PHENOMENA.     For  the  use  of 

Colleges,  Academies,  and  Families.  In  one  large  volume,  imperial  quarto,  handsomely  and 
strongly  bound,  with  twenty-six  Plates,  engraved  and  colored  in  the  best  style.  Together  wuh 
112  pages  of  descriptive  letter-press,  and  a  very  copious  Index. 


18 


BLANCHARD    &   LEA'S   MEDICAL 


JONES  (T.   WHARTON),   F.  R.  S.,  iltc.  , 

THE   PETNCIPLES  AND   PRACTICE  OF    OPHTHALMIC    MEDICINE 

AND  SURGERY.    Edited  l)y  Isaac  Hays,  M.  D.,  &c.     In  one  very  neat  volume,  large  royal 
12nio.,  of  529  pages,  with  four  plates,  plain  or  colored,  and  ninety-eight  wood-cuts. 


We  are  confident  that  the  reader  will  find,  on 
perusal,  that  the  execution  of  the  work  amply  fulfils 
the  promise  of  the  preface,  and  sustains,  in  every 
point  the  already  high  reputation  of  the  author  as 
an  ophthalmic  surgeon  as  well  as  a  physiologist 
and  pathologist.  The  book  is  evidently  the  result 
of  much  labor  and  research,  and  has  been  written 
with  the  greatest  care  and  attention;  it  possesses 
that  best  quality  which  a  general  work,  like  a  sys- 
tem or  manual  can  show,  viz. :  the  quality  of  having 
all  the  materials  whencesoever  derived,  so  thorough- 
ly wrought  up,  and  digested  in  the  author's  mind, 
as  to  come  forth  with  the  freshness  and  impressive- 
ness  of  an  original  production.  We  regret  that  we 
i'.ave  received  the  b(>ok  at  so  late  a  period  as  pre- 
cludes our  giving  more  than  a  mere  notice  of  it,  as, 


although  essentially  and  necessarily  a  compilation,  it 
contains  many  things  which  we  should  be  glad  tro 
reproduce  in  our  pages  whether  in  the  shape  of  new 
pathological  views,  of  old  errors  corrected,  or  of 
sound  principles  of  practice  in  doubtful  cases  dearly 
hiid  down.  But  we  dare  say  most  of  our  readers 
will  shortly  have  an  opportunity  of  seeing  these  in 
their  original  locality,  as  we  entertain  little  doubi 
that  this  book  will  become  what  its  author  hoped  it 
might  become,  a  manual  for  daily  reference  ami 
consultation  by  the  student  and  the  general  practi- 
tioner. The  work  is  marked  by  that  correctness, 
clearness,  and  precision  of  style  which  distinguish 
all  the  productions  of  the  learned  author. — British 
and  Foreign  Medical  Review. 


KIRKES  (WILLIAM   SENHOUSE),    M.  D., 

Demonstrator  of  Morbid  Anatomy  at  St.  Bartholomew's  Hospital,  &c. 


and 


JAMES   PAGET,  F.  R.  S., 

Lecturer  on  General  Anatomy  and  Physiology  in  St.  Bartholomew's  Hospital. 

A  MANUAL  OF  PHYSIOLOGY.  Second  American,  from  the  second  and 
improved  London  edition.  With  one  hundred  and  sixty-five  illustrations.  In  one  large  ami 
handsome  royal  12nio.  volume,     pp.550.     {Just  Issued.) 


In  the  present  edition,  the  Manual  of  Physiology 
has  been  brought  up  to  the  actual  condition  of  the 
science,  and  fully  sustains  the  reputation  which  it 
has  already  so  deservedly  attained.  We  consider 
the  work  of  MM,  Kirkes  and  Paget  to  constitute  one 
of  the  very  best  handbooks  of  Physiology  we  possess 
—presenting  just  such  an  outline  of  the  science,  com- 
prising an  account  of  its  leading  facts  and  generally 
admitted  principles,  as  the  student  requires  during 
his  attendance  upon  a  course  of  lectures,  or  for  re- 
ference whilst  preparing  for  examination.  The  text 
IS  fully  and  ably  illustrated  by  a  series  of  very  supe- 
rior wood-engravings,  by  which  a  comprehension  of 
some  of  the  more  intricate  of  the  subjects  treated  of 
18  greatly  facilitated.— 4m.  Medical  Journal. 

We  need  only  say,  that,  without  entering  into  dis- 
cussions of  unsettled  questicms,  it  contains  all  the 
recent  improvements  in  this  department  of  medical 
science.  _  For  the  student  beginning  this  study,  and 
the  practitioner  who  has  but  leisure  to  refresh  his 
memory,  this  book  is  invaluable,  as  it  contains  all 
that  It  is  important  to  know,  without  special  details, 
which  are  read  with  interest  only  by  those  who 
wmild  make  a  specialty,  or  desire  to  possess  a  criti- 
cal knowledge  oi  the  Buhiocx..— Charleston  Medical 
Journal. 

One  of  the  best  treatises  that  can  be  put  into  the 
hands  of  the  student.- London  Medical  Gazette. 


The  general  favor  with  which  the  first  edition  of 
this  Avork  was  received,  and  its  adoption  as  a  favor- 
ite text-book  by  many  of  our  colleges,  will  insure  a 
large  circulation  to  this  improved  edition.  It  will 
fully  meet  the  wants  of  the  student.  —  Southern 
Med.  and  Surg.  Journal. 

It  possesses  the  especial  merit  of  being  clear  and 
concise,  and  at  the  same  time  affording  a  good  out- 
line of  Physiology, — Western  Lancet. 

Numerous  new  and  superior  illustrations  have 
been  introduced  for  the  purpose  of  making  the  sub- 
ject of  more  easy  comprehension  by  the  student. 
This  edition  has  evidently  been  prepared  with  great 
care,  and  is  handsomely  printed  on  good  paper,  and 
will  prove  a  very  valuable  book  for  the  student  in 
acquainting  himself  with  all  the  leading  well-es- 
tablished facts  in  physiology,  and  for  the  practitioner 
as  a  work  of  reference. — New  York  Medical  Times. 

Particularly  adapted  to  those  who  desire  to  pos- 
sess a  concise  digest  of  the  facts  of  Human  Physi- 
ology.— British  and  Foreign  Med.-Chirurg.  Revieiv. 

We  conscientiously  recommend  it  as  an  admira- 
ble "  Handbook  of  Physiology,"— Loncion  Journal 
of  Medicine. 


KNAPP  (F.),  PH.  D.,  &.C. 
TECHNOLOGY ;  or,  Chemistry  applied  to  the  Arts  and  to  Manufactures.  Edited, 
with  numerous  Notes  and  Additions,  by  Dr.  Edmund  Ronalds  and  Dr.  Thomas  Richardson. 
t  irst  American  edition,  with  Notes  and  Additions,  by  Prof.  Walter  R.  Johnson.  In  two  hand- 
some  ociavo  volumes,  printed  and  illustrated  in  the  highest  style  of  art,  with  about  five  hundred 
wood-engravings. 


LEHMANN. 
PHYSIOLOGICAL    CHEMISTRY.     Translated  by  George  E.  Day,  M.  D. 

{Freparuig.) 


In  one  very  large  octavo  volume. 


LEE  (ROBERT),   M.  D.,  F.  R.  S.,  &c. 
CLINICAL    MIDWIFERY;    comprising  the   Histories  of  Five  Hundred  and 
Forty-five  Cases  of  Difficult,  Preternatural,  and  Complicated  Labor,  with  Commentaries.    From 
the  second  London  edition.    In  one  royal  12mo.  volume,  extra  cloth,  of  238  pages. 


AND    SCIENTIFIC   PUBLICATIONS, 


19 


LAWRENCE  (W.),   F.  R.  S.,  &c. 
A  TREATISE    ON    DISEASES    OF    THE    EYE.     Third  American  e-Iition, 

much  improved  and  enlarged.  "With  over  two  hundred  illustrations.  By  Isaac  Hays,  M.  D., 
Surgeon  to  Wills  Hospital,  Philadelphia,  &c.  In  one  very  large  and  handsome  octavo  volume, 
of  over  eight  hundred  pages.     This  new  edition  to  be  ready  by  July. 

This  work,  by  far  the  largest  and  most  comprehensive  on  the  subject  wilhin  reach  of  the  profes- 
sion in  this  country,  will  receive  an  entire  revision  on  the  part  of  the  editor.  Brought  up  in  this 
manner  to  the  most  advanced  state  of  science,  and  presenting  an  equal  improvement  over  its.  prede- 
cessors as  regards  mechanical  execution,  it  is  confidently  presented  as  worthy  of  the  extended  repu- 
tation which  it  has  hitherto  enjoyed. 


BY   THE   SAME    AUTHOR. 


A  TREATISE  ON  RUPTURES;  from  the  fifth  London  edition. 

volume,  sheep,  480  pages. 


In  one  octavo 


LEIDY    (JOSEPH),  M.  D. 

Professor  of  Anatomy  in  the  University  of  Pennsylvania,  &c. 

ATLAS  OF  PATHOLOaiCAL   HISTOLOGY.     By  Gottlieb  Gluge,  M.  D. 

Translated  from  the  German,  with  Additions,  by  Joseph  Leidy,  M.  D  ,  Professor  of  Anatomy 
m  the  University  of  Pennsylvania.  In  one  vol.,  large  imperial  quarto,  with  320  figures,  plain 
and  colored,  on  twelve  plates. 

BY  the  same   author. 

HUMAN  ANATOMY.     By  Jones  Quain,  M.  D.    From  the  fifth  London  edition. 

Edited  by  Richard  Quain,  F.  R.  S.,  and  William  Sharpey,  M.  D.,  F.R.  S.,  Professors  of 
Anatomy  and  Physiology,  in  University  College,  London.  Revised,  with  Notes  and  Additions, 
by  Joseph  Leidy,  M.  D.,  Professor  of  Anatomy  in  the  University  of  Pennsylvania.  Complete  in 
two  large  8vo.  vols,  of  about  1300  pages,  beautifully  illustrated  with  over  500  engravings  on  wood. 


LISTON   (ROBERT),   F.  R.  S.,  &c. 
LECTURES  ON  THE  OPERATIONS  OF  SURGERY,  and  on  Diseases  and 

Accidents  requiring  Operations.     Edited,  with  numerous  Additions  and  Alterations,  by  T.  D. 
MiJTTER,  M.  D.     In  one  large  and  handsome  octavo  volume,  of  566  pages,  with  216  wood-cuts. 


We  can  only  sa^"-,  in  conclusion,  that  Liston's 
Lectures,  with  Matter's  additions,  should  be  in 
every  surgeon's  library,  and  in  every  student's 
band,  who  wishes  to  post  up  his  surgical  knowledge 
to  the  present  moment. — N.  Y.  Journ.  of  Medicine. 


It  is  a  compendium  of  the  modern  prnctice  of  Sur- 
gery as  complete  and  accurate  as  any  treatise  of 
similar  dimensions  in  the  English  language. — West- 
ern Lancet. 


LALLEMAND  (M.). 
THE  CAUSES,  SYMPTOMS,  AND  TREATMENT  OF  SPERMATOR- 

RHGEA.     Translated  and  edited  by  Henry  J.  McDouGAL.    In  one  volume,  octavo,  320  pages. 
Second  American  edition.     [Now  Ready.) 


LARDNER  (DIONYSIUS),  D.  C.  L.,  8lc. 
HANDBOOKS  OF  NATURAL  PHILOSOPHY  AND  ASTRONOMY. 

First  Course,  containing  Mechanics,  Hydrostatics,  Hydraulics,  Pneumatics,  Sound,  and  Optics. 
In  one  large  royal  ]2ino.  volume,  of  750  pages,  with  424  wood-cuts.  Second  Course,  containing 
Heat,  Electricity,  Magnetism,  and  Galvanism,  one  volume,  large  royal  12mo.,  of  450  pages,  with 
250  illustrations.  Third  Course  {nearly  ready),  will  contain  Meteorology  and  Astronomy,  with 
numerous  steel-plates  and  wood-cuts.  Revised,  with  numerous  Additions,  by  the  American  editor. 


The  work  furnishes  a  very  clear  and  satisfactory 
account  of  our  knowledge  in  the  important  depart- 
ment of  science  of  which  it  treats.  Although  the 
medical  schools  of  this  country  do  not  include  the 
study  of  physics  in  their  course  of  instruction,  yet 
no  student  or  practitioner  should  he  ignorant  of  its 
laws.  Besides  being  of  constant  application  in  prac- 
tice, such  knowledge  is  of  inestimable  utility  in  fa- 
cilitating the  study  of  other  branches  of  science.  To 
students,  then,  and  to  those  who,  having  already  en- 
tered upon  the  active  pursuits  of  business,  are  desir- 
ous to  sustain  and  improve  their  knowledge  of  the 
general  truths  of  natural  philosophy,  we  can  recom- 
mend this  work  as  sbpplying  in  a  clear  and  satis 


factory  manner  the  information  they  desire. — The 
Virginia  Med.  and  Surg.  Journal, 

The  present  treatise  is  a  most  complete  digest  of 
all  that  has  been  developed  in  rclati<in  to  the  great 
forces  of  nature,  Heat,  Magnetism,  and  Electricity. 
Their  laws  are  elucidated  in  a  manner  both  pleasing 
and  familiar,  and  at  the  same  time  perfectly  intelli- 
gible to  the  student.  The  illustrations  are  suffi- 
ciently numerous  and  appropriate,  and  altc^gethcr 
we  can  cordially  recommend  the  work  as  wt-ll-de- 
serving  the  notice  both  of  the  practising  physician 
and  the  student  of  medicine.— TAe  Med.  Examiner. 


20 


BLANCHARD   &  LEA'S   MEDICAL 


MEIGS  (CHARLES   D.),  M.  D., 

Professor  of  Obstetrics,  &c.,  in  the  Jefferson  Medical  College.  Philadelphia. 

OBSTETRICS:  THE  SCIENCE  AND   THE   ART.     Second  edition,  revised 

and  improved.     With  one  hundred  and  thirty-one  illustrations.     In  one  beautifully  printed  octavo 
volume,  of  seven  hundred  and  fifty-tv/o  large  pages.     {Lately  Published.) 

The  rapid  demand  for  a  second  edition  of  this  work  is  a  sufficient  evidence  that  it  has  supplied 
a  desideratum  of  the  profession,  notvv'ilhstanding  the  numerous  treatises  on  the  same  subject  which 
have  appeared  within  the  last  few  years.  Adopting-  a  system  of  his  own,  the  author  has  combined 
the  leading  principles  of  his  interesting  and  difficult  subject,  with  a  thorough  exposition  of  its  rules 
oi' practice,  presenting  the  results  of  long  and  extensive  experience  and  of  familiar  acquaintanoe 
with  all  the  modern  writers  on  this  department  of  medicine.  As  an  American  Treatise  on  Mid- 
wifery, which  has  at  once  assumed  the  position  of  a  classic,  it  possesses  peculiar  claims  to  the  at- 
tention and  study  of  the  practitioner  and  student,  while  the  numerous  alterations  and  revisioriS 
which  it  has  undergone  in  the  present  edition  are  shown  by  the  great  enlargement  of  the  woric, 
which  is  not  only  increased  as  to  the  size  of  the  page,  but  also  in  the  number.  Among  other  addi- 
tions may  be  mentioned 

A  NEW  AND  IMPORTANT  CHAPTER  ON  "CHILD-BED  FEVER." 


As  an  elementary  treatise — concise,  but,  withal, 
clear  and  comprehensive — we  know  of  no  one  better 
adapted  for  tlie  use  of  the  student;  while  the  young 
practitioner  will  find  in  it  a  body  of  sound  doctrine, 
and  a  series  of  excellent  practical  directions,  adapted 
to  all  the  conditions  of  the  various  forms  of  labor 
and  their  results,  which  he  will  be  induced,  we  are 
persuaded,  again  and  again  to  consult,  and  always 


with  profit.  It  has  seldom  been  our  lot  to  peruse  a 
work  upon  the  subject,  from  which  we  have  re- 
ceived greater  satisfaction,  and  which  we  believe  to 
be  better  calculated  to  communicate  to  the  student 
correct  and  definite  views  upon  the  several  topics 
embraced  within  the  scope  of  its  teachings. — Am. 
Journal  of  the  Medical  Sciences. 


BY   THE    SAME   AUTHOR. 


WOMAN :  HER  DISEASES  AND  THEIR  REMEDIES.     A  Series  of  Lee- 

tures  to  his  Class.     Second  edition,  revised.    In  one  large  and  beautifully  printed  octavo  volume, 
Oif  nearly  seven  hundred  large  pages. 


It  contains  a  vast  amount  of  practical  knowledge, 
by  one  who  has  accurately  observed  and  retained 
the  experience  of  many  years,  and  who  tells  the  re- 
sult in  a  free,  familiar,  and  pleasant  manner. — Duh- 
Uii  Quarterly  Journal. 

There  is  an  off-hand  fervor,  a  glow,  and  a  warm- 
heartedness infecting  the  effort  of  Dr.  Meigs,  which 
is  entirely  captivating,  and  which  absolutely  hur- 
ries the  reader  through  from  beginning  to  end.  Be- 
sides, the  book  teems  with  solid  instruction,  and 
it  shows  the  very  highest  evidence  of  ability,  viz., 
the  clearness  with  which  the  information  is  pre- 
sented. We  know  of  no  better  test  of  one's  under- 
standing a  subject  tlian  the  evidence  of  the  power 
of  lucidly  explaining  it.  The  most  elementary,  as 
well  as  the  obscurest  subjects,  under  the  pencil  of 
Prof.  Meigs,  are  isolated  and  made  to  stand  out  in 
such  bold  relief,  as  to  produce  distinct  impressions 
upon  the  mind  and  memory  of  the  reader.  —  The 
Charleston  Med.  Journal. 


Professor  Meigs  has  enlarged  and  amended  this 
great  work,  for  such  it  unquestionably  is,  having 
passed  the  ordeal  of  criticism  at  home  and  abroacl, 
but  been  improved  thereby  ;  for  in  this  new  edition 
the  author  has  introduced  real  improvements,  and 
increased  the  value  and  utility  of  the  book  im- 
measurably. It  presents  so  many  novel,  bright, 
and  sparkling  thoughts;  such  an  exuberance  of  new 
ideas  on  almost  every  page,  that  we  ccmfess  our- 
selves to  have  become  enamored  with  the  book 
and  its  author  ;  and  cannot  withhold  our  congratu- 
lations from  our  Philadelphia  confreres,  that  such  a 
teacher  is  in  their  service.  We  regret  that  our 
limits  will  not  allo^v  of  a  more  extended  notice  of 
this  work,  but  must  content  ourselves  with  thus 
commending  it  as  worthy  of  diligent  perusal  by 
physicians  as  well  as  students,  who  are  seeking  to 
be  thoroughly  instructed  in  the  important  practical 
subjects  of  which  it  treats. — N.  Y.  Bled.  Gazette. 


BY  THE  SAME  AUTHOR. 

OBSERVATIONS   ON    CERTAIN    OF    THE    DISEASES    OF    YOUNG 

CHILDREN.    In  one  handsome  octavo  volume,  of  214  pages. 

It  puts  forth  no  claims  as  a   systematic  work,  J  carbuncle,  and  its  fascinating  pages  often  begailed 
but  contains  an  amount  of  valuable  and  useful  mat-  I  us  into  forgetfulness  of  agonizing   pain.     May  it 

teach  others  to  relieve  the  afflictions  of  the  young. — 
Western  Journal  of  Medicine  and  Surgery. 

The  work  before  us  is  undoubtedly  a  valuable 
addition  to  the  fund  of  information  which  has  al- 
ready been  treasured  up  on  the  subjects  in  question. 
It  is  practical,  and  therefore  eminently  adapted  to 
the  general  practiticmer.    Dr.  Meigs's  works  have 


ter,  scarcely  to  be  found  in  the  same  space  in  our 
home  literature.  It  cannot  but  prove  an  acceptable 
offerinof  to  the  profession  at  large.— JV.  Y.  Journal  of 
Medicine. 

We  take  much  pleasure  in   recommending  this 
excellent  little  work   to  the  attention   of  medical 

practitioners.     It  deserves  their  attention,  and  nf-     ..._  ^ , _. . ^_  _ 

ter  they  commence  its  perusal,  they  will  not  wil-  I  the  "same   fa'scination  which  belongs  to  himself.— 
Iingly  abandon    it,   until   they  have    mastered    its    Medical  Examiner. 
contents.    We  read  the  work  while  suffering  from  a  I 


ON    THE    NATURE,    ,    _ 

FEVER.    In  one  handsome  octavo  volume. 


BY  THE  SAME  AUTHOR.     {Preparing:) 

SIGNS,    AND    TREATMENT 


OF    PUERPERAL 


BY  THE  SAME  AUTHOR.     (Prepariiig.) 

A  TREATISE  ON  ACUTE   AND   CHRONIC   DISEASE   OF  THE  NECK 

OF  THE  UTERUS.     With  numerous  plates,  drawn  and  colored  from  nature  in  the  highest 
style  of  art.     In  one  handsome  octavo  volume. 


AND   SCIENTIFIC    PUBLICATIONS, 


21 


MILLER  (JAMES),   F.  R.  S.  E., 

Professor  of  Surgery  in  the  University  of  Edinburgh.  &;c. 

PRINCIPLES  OF  SURGERY.     Third  American,  from  the  second  and  revised 

Edinburgh  edition.  Revised,  with  Additions,  by  F.  W.  Sakgent,  M.  D.,  author  of  "  Minor  Sur- 
gery," &c.  In  one  large  and  very  beautiful  volume,  of  seven  hundred  and  fifty-two  pages,  with 
two  hundred  and  forty  exquisite  illustrations  on  wood.     (Extensively  used  as  a  text-book.) 

The  publishers  have  endeavored  to  render  the  present  edition  of  this  work,  in  every  point  of  me- 
dianieal  execution,  worthy  of  its  very  high  reputation,  and  they  confidently  present  it  to  the  pro- 
fession as  one  of  the  handsomest  volumes  as  yet  issued  in  this  country. 

This  edition  is  far  superior,  both  in  the  abundance  ]  guage.  This  opinion,  deliberately  formed  after  a 
and  quality  of  its  material,  to  any  of  the  preceding,  careful  study  of  the  first  edition,  we  have  had  no 
We  hope  it  will  be  extensively  read,  and  the  sound  cause  to  change  on  examining  the  second.  This 
principles  wliich  are  herein  taught  treasured  up  for  edition  has  undergone  thorough  revision  by  the  au- 
future  application.  The  work  takes  rank  with  thor;  many  expressions  have  been  modified,  and  a 
Watson's  Practice  of  Physic  ;  it  certainly  does  not  I  mass  of  new  matter  introduced.  The  book  is  got  up 
fall  behind  that  great  work  in  soundness  of  princi-  in  the  finest  style,  and  is  an  evidence  of  the  progress 
pie  or  depth  of  reasoning  and  research.  No  physi-  of  typography  in  our  country. — Charleston  Medical 
cian  who  values  his  reputation,  or  seeks  the  interests  I  Journal  and  Review. 
t»f  his  clients,  can  acquit  himself  before  his  God  and  j 
the  world  without  making  himself  familiar  with  the  | 
sound  and  philosophical  views  developed  in  the  fore-  ' 
going  book. — New  Orleans  Medical  and  Surgical 
Journal. 


Without  doubt  the  ablest  exposition  of  the  prin- 
ciples of  that  branch  of  the  healing  art  in  any  lan- 


We  recommend  it  to  both  student  and  practitioner, 
feeling  assured  that  as  it  now  comes  to  us,  it  pre- 
sents the  most  satisfactory  exposition  of  tlie  modern 
doctrines  of  the  principles  of  surgery  to  be  found  in 
any  volume  in  any  language. — N.  Y.  Journal  of 
Medicine. 


BY  THE  SAME  AUTHOR.     (Now  Ready.) 

THE  PRACTICE  OF   SURGERY.     Third  American  from  the  second  Eiin- 

burgh  edition.  Edited,  with  Additions,  by  F.  \V.  Sargent,  M.  D  ,  one  of  the  Surgeons  to  Will's 
Hospital,  &-C.  Illustrated  by  three  hundred  and  nineteen  engravings  on  wood.  In  one  large 
octavo  volume,  of  over  seven  hundred  pages. 

This  new  edition  will  be  found  greatly  improved  and  enlarged,  as  well  by  the  addition  of  much 
new  matter  as  by  the  introduction  of  a  large  and  complete  series  of  handsome  illustrations.  An 
equal  improvement  exists  in  the  mechanical  execution  of  the  work,  rendering  it  in  every  respect 
a  companion  volume  to  the  "  Principles." 

We  had  occasion  in  a  former  number  of  this  .Tour- 
nal,  to  speak  in  deservedly  high  terms  of  Professor 
Miller's  work  on  the  "  Principles  of  Siirgery,"  and 
we  are  happy  to  be  able  to  pronounce  an  equally 
favorable  judgment  on  the  manner  in  which  the  pre- 
sent volume  is  executed.  *  *  #  We  feel  no 
liesitaticm  in  recommending  Professor  Miller's  two 
volumes  as  affording  to  the  student  what  the  author 
intended,  namely,  a  complete  text-book  of  Surgery. 
— British  and  Foreign  Medical  Review. 

Although,  as  we  are  modestly  informed  in  the 
preface,  it  is  not  put  forth  in  rivalry  of  the  excel- 


lent works  on  Practical  Surgery  which  already 
exist,  we  think  we  may  take  upon  ourselves  to  say 
that  it  will  form  a  very  successful  and  formidable 
rival  to  most  of  them. — Northern  Journ.  of  Medicine. 

Taken  together  they  form  a  very  condensed  and 
complete  system  of  Surgery,  not  surpassed,  as  a 
text-book,  by  any  work  with  which  we  are  ac- 
quainted.—J/^  and  Ind.  Med.  and  Surg.  Journal. 

Mr.  Miller  has  said  more  in  a  few  words  than  any 
writer  since  the  days  of  Celsus.— iV.  O.  Med.  and 
Surg.  Journal. 


MALGAIGNE  (J.  F.). 

OPERATIVE  SURGERY,  based  on  Normal  and  Pathological  Anatomy.  Trans- 
lated from  the  French,  by  Frederick  Brittan,  A.  B.,  M.  D.  With  numerous  illustrations  on 
wood.     In  one  handsome  octavo  volume,  of  nearly  six  hundred  pages. 


AVe  have  long  been  accustomed  to  refer  to  it  as  one 
of  the  most  valuable  text-books  in  our  library. — 
Buffalo  Med.  and  Surg.  Journal. 

Certainly  one  of  the  best  books  published  on  ope- 
rative surgery. — Edinburgh  Medical  Journal. 


To  express  in  a  few  words  our  opinion  of  Mal- 
gaigne^  work,  we  unhesitatingly  pronounce  it  the 
very  best  guide  in  surgical  operations  that  has  come 
before  the  profession  in  any  language. — Charleston 
Med.  and  Surg.  Journal. 


MOHR  (FRANCIS),  PH.  D.,  AND  REDWOOD  (TH  EOPH  I  LUS). 

PRACTICAL  PHARMACY.  Comprising  the  Arrangements,  Apparatus,  and 
Manipulations  of  the  Pharmaceutical  Shop  and  Laboratory.  Edited,  with  extensive  Additions, 
by  Prof.  William  Procter,  of  the  Philadelphia  College'  of  Pharmacy.  In  one  handsomely 
printed  octavo  volume,  of  570  pages,  with  over  500  engravings  on  wood. 

sary  thereto.  On  these  matters,  this  work  is  very 
full  and  complete,  and  details,  in  a  style  uncom- 
monly clear  and  lucid,  not  only  the  more  compli- 
cated and  difficult  processes,  but  those  not  less  im- 
portant ones,  the  most  simple  and  common.— Buffalo 
Medical  Journal. 

The  country  practitioner  who  is  obliged  to  dis- 
pense his  own  medicines,  will  find  it  a  most  valuable 
assistant. — Monthly  Journal  and  Retrospect. 


It  is  a  book,  however,  which  will  be  in  the  hands  ! 
of  almost  everyone  who  is  much  interested  in  phar- 
maceutical operations,  as  we  know  of  no  other  pub- 
lication so  well  calculated  to  fill  a  void  long  felt. — 
Medical  Examiner . 

The  book  is  strictly  practical,  and  describes  only 
manipulations  or  methods  of  performing  the  nume- 
rous processes  the  pharmaceutist  has  to  go  through, 
in  the  preparation  and  manufacture  of  medicines, 
together  with  all  the  apparatus  and  fixtures  neces- 


22 


BLANCHARD   &   LEA'S   MEDICAL 


MACLISE   (JOSEPH),    SURGEON. 

SURGICAL  ANATOMY. 

FORMING  ONE   VOLUME,   VERY   LARGE    IMPERIAL   QUARTO. 

"With  Sixty-eight  larga  and  splendid  Plates,  drawn  in  the  test  style,  and  beautifully  colored. 
Containing  one  hundred  and  ninety  Figures,  many  of  them  the  size  of  life. 

TOGETHER   WITH    COPIOUS    AND   EXPLANATORY    LETTER-PRESS. 

Strongly  and  handsomely  bound  in  extra  cloth,  being  one  of  the  cheapest  and  best  executed  Surgical 
works  as  yet  issued  in  this  country. 

Copies  can  be  sent  by  mail,  in  five  parts,  done  up  in  stout  covers. 

This  great  work  being  now  concluded,  the  publishers  confidently  present  it  to  the  attention  of  the 
profession  as  worthy  in  every  respect  of  their  approbation  and  patronage.  No  complete  work  of 
the  kind  has  yet  beeii  published  in  the  English  language,  and  it  therefore  will  supply  a  want  long 
felt  in  this  country  of  an  accurate  and  comprehensive  Atlas  of  Surgical  Anatomy  to  which  the 
student  and  practitioner  can  at  all  times  refer,  to  ascertain  the  exact  relative  position  of  the  various 
fKJrtions  of  the  human  frame  towards  each  other  and  to  the  surface,  as  well  as  their  abnormal  de- 
viations. The  importance  of  such  a  work  to  the  student  in  the  absence  of  anatomical  material,  and 
to  the  practitioner  when  about  attempting  an  operation,  is  evident,  while  the  price  of  the  book,  not- 
withstanding the  large  size,  beauty,  and  finish  of  the  very  numerous  illustrations,  is  so  low  as  to 
place  it  within  the  reach  of  every  member  of  the  profession.  The  publishers  therefore  confidently 
anticipate  a  very  extended  circulation  for  this  magnificent  work. 


One  of  the  greatest  artistic  triumphs  of  the  age 
in  Surgical  Anatomy. — British  American  Medical 
Journal. 

Too  much  cannot  be  said  in  its  praise;  indeed, 
we  have  not  language  to  do  it  justice. — Ohio  Medi- 
cal and  Surgical  Journal. 

The  most  admirable  surgical  atlas  we  have  seen. 
To  the  practitioner  deprived  of  demonstrative  dis- 
sections upon  the  human  subject,  it  is  an  invaluable 
companion.— iV.  J.  Medical  Reporter. 

The  most  accurately  engraved  and  beautifully 
colored  plates  we  have  ever  seen  in  an  American 
book — one  of  the  best  and  cheapest  surgical  works 
ever  published.— ^w^aio  Medical  Journal. 

It  is  very  rare  that  so  elegantly  printed,  so  well 
illustrated,  and  so  useful  a  work,  is  offered  at  so 
moderate  a  price. — Charleston  Medical  Journal. 

Its  plates  can  boast  a  superiority  which  places 
them  almost  beyond  the  reach  of  competition. — Medi- 
eal  Examiner. 

Every  practitioner,  we  think,  should  have  a  work 
of  this  kind  within  reach.— Southern  Medical  and 
Surgical  Journal. 

No  such  lithographic  illustrations  of  surgical  re- 
gions have  hitherto,  we  think,  been  given. — Boston 
Medical  and  Surgical  Journal. 

As  a  surgical  anatomist,  Mr.  Maclise  has  proba- 
bly no  superior.— British  and  Foreign  Medico-Chi- 
rurgical  Review. 

Of  great  value  to  the  student  engaged  in  dissect- 
ing, and  to  the  surgeon  at  a  distance  from  the  means 
ot  keeping  up  his  anatomical  knowledge.— Jfgrftca^ 
Times. 

The  mechanical  execution  cannot  be  excelled.— 
Transylvania  Medical  Journal. 

A  work  which  has  no  parallel  in  point  of  accu- 
racy and  cheapness  in  the  English  language.- JV.  Y 
Journal  of  Medicine.    ■ 

To  all  engaged  in  the  study  or  practice  of  their 
profession,  such  a  work  is  almost  indispensable.— 
Dublin  Quarterly  Medical  Journal. 

No  practitioner  whose  means  will  admit  should 
fail  to  possess  it. — Ranking' s  Abstract. 

Country  practitioners  will  find  these  plates  of  im- 
mense value.— iV.  r.  Medical  Gazette. 

We  are  extremely  gratified  to  announce  to  the 
profession  the  completion  of  this  truly  magnificent 
work,  which,   as  a  whole,   certainly   stands   unri- 


vailed,  both  for  accuracy  of  drawing,  beauty  of 
coloring,  and  all  the  requisite  explanations  of  the 
subject  in  hand.  To  the  publishers,  the  profession 
in  America  is  deeply  indebted  for  placing  such  a 
valuable,  such  a  useful  work,  at  its  disposal,  and 
at  such  a  moderate  price.  It  is  one  of  the  most 
finished  and  complete  pictures  of  Surgical  Anato- 
my ever  offered  to  the  profession  of  America. — 
With  these  plates  before  them,  the  student  and  prac- 
titioner can  never  be  at  a  loss,  under  the  most  despe- 
rate circumstances.  We  do  not  intend  these  for 
commonplace  compliments.  AVe  are  sincere;  be- 
cause we  know  the  work  will  be  found  invaluable 
to  the  young,  no  less  than  the  old,  surgeon.  We 
have  not  space  to  point  out  its  beauties,  and  its 
merits;  but  we  speak  of  it  en  masse,  as  a  whole, 
and  strongly  urge — especially  those  who,  from  their 
position,  may  be  debarred  the  privilege  and  opportu- 
nity of  inspecting  the  fresh  subject,  to  furnish  them- 
selves with  the  entire  work. — The  New  Orleans 
Medical  and  Surgical  Journal. 

This  is  by  far  the  ablest  work  on  Surgical  Ana- 
tomy that  has  come  under  our  observation.  We 
know  of  no  other  work  that  would  justify  a  stu- 
dent, in  any  degree,  for  neglect  of  actual  dissec- 
tion. A  careful  study  of  these  plates,  and  of  the 
commentaries  on  them,  would  almost  make  an  ana- 
tomist of  a  diligent  student.  And  to  one  who  has 
studied  anatomy  by  dissection,  this  work  is  invalu- 
able as  a  perpetual  remembrancer,  in  matters  of 
knowledge  that  may  slip  from  the  memory.  The 
practitioner  can  scarcely  consider  himself  equipped 
for  tlie  duties  of  his  profession  without  such  a  work 
as  this,  and  this  has  no  rival,  in  his  library.  Jn 
those  sudden  emergencies  that  so  often  arise,  and 
which  require  the  instantaneous  command  of  minute 
anatomical  knowledge,  a  work  of  this  kind  keeps  the 
details  of  the  dissecting-room  perpetually  fresh  in  the 
memory.  We  appeal  to  our  readers,  whether  any 
one  can  justifial)ly  undertake  the  practice  of  medi- 
cine who  is  not  prepared  to  give  all  needful  assist- 
ance, in  all  matters  demanding  immediate  relief. 
We  repeat  that  no  medical  library,  however  large, 
can  be  complete  without  Maclise's  Surgical  Ana- 
tomy. The  American  edition  is  well  entitled  to  the 
confidence  of  the  professi(m,  and  should  command, 
among  them,  an  extensive  sale.  Tlie  investment  of 
the  amount  of  the  cost  of  this  work  will  prove  to 
be  a  very  profitable  one,  and  if  practitioners  would 
qualify  themselves  thoroughly  with  such  important 
knowledge  as  is  contained  in  works  of  this  kind, 
there  would  be  fewer  of  them  sighing  for  employ- 
ment. Tlie  medical  profession  should  spring  towards 
such  an  opportunity  as  is  presented  in  this  republica- 
tion, to  encourage  frequent  repetitions  of  American 
enterprise  of  this  kind.— TAe  Western  Journal  of 
Medicine  and  Surgery. 


The  very  low  price  at  which  this  work  is  furnished,  and  the  beauty  of  its  execution, 
require  an  extended  sale  to  compensate  the  pubUshers  for  the  heavy  expenses  incurred. 


AND    SCIENTIFIC    PUBLICATIONS.  23 

MULLER  (PROFESSOR  J.),   M.  D. 
PRINCIPLES  OF  PHYSICS   AND   METEOROLOGY.     Edited,  with  Addi- 

lions,  by  R.  Eglesfeld  Griffith,  M.  D.     In  one  large  and  handsome  octavo  volume,  extra 
doth,  with  C50  wood-cuts,  and  two  colored  plates. 

The  Physics  of  MQller  is  a  work  superb,  complete.  |  tion  to  the  scientific  records  of  this  country  may  l>e 
unique  :  the  greatest  want  known  to  English  Science  |  duly  estimated  by"  the  fact  that  the  cost  of  the  origi- 
could  not  have  been  better  supplied.  The  work  is  I  nal  drawings  and  engravings  alone  has  exceeded  the 
of  surpassing  interest.     The  value  of  this  contribu-  |  sum  of  £2,000. — Lancet. 


MAYNE  (JOHN),  M.  D.,  M.  R.  C.  S.,  &c. 
A  DISPENSATORY  AND  THERAPEUTICAL  REMEMBRANCER.   Com- 

prising-  the  entire  lists  of  Materia  Mediea,  with  every  Practical  Formula  contained  in  the  three 
Britij^h  Pharmacopoeias.  With  relative  Tables  subjoined,  illu>trating,  by  upwards  of  six  hundred 
and  sixty  examples,  the  Extemporaneous  Forms  and  Combinations  suitable  for  the  different 
Medicines.  Edited,  with  the  addition  of  the  Formulae  of  the  United  Stales  Pharmacopoeia,  by 
R.  Eglesfeld  Gkiffith,  M.  D.    In  one  12mo.  volume,  extra  cloth,  of  over  300  large  pages. 


MATTEUCCI  (CARLO). 
LECTURES  ON  THE  PHYSICAL  PHENOMENA  OF  LIVING  BEINGS. 

Edited  by  Pereira.     In  one  neat  royal  12mo.  volume,  extra  cloth,  with  cuts,  388  pages. 


MARKWICK  (ALFRED). 
A  GUIDE   TO   THE   EXAMINATION  OF   THE   URINE   IN   HEALTH 

AND  DISEASE.    Royal  12mo.     (See  Manuals  on  Blood  and  Urine.) 


MEDLOCK  (HENRY),  AND   F.  SGHOEDLER. 

BOOK  OF  NATURE;  or  Elements  of  the  Science  of  Physics,  Astronomy,  Chem- 
istry, Mineralogy,  Geology,  Botany,  Zoology,  and  Physiology.  (See  Schoedler.)  In  one  vol., 
large  12mo.     An  admirable  work  for  families  and  District  Schools. 


NEILL  (JOHN),   M.  D., 

Demonstrator  of  Anatomy  in  the  University  of  Pennsylvania;  Surgeon  to  the  Pennsylvania  Hospital,  &c.; 

and 
FRANCIS  GURNEY   SMITH,   M.D., 
Professor  of  Institutes  of  Medicine  in  the  Pennsylvania  Medical  College. 

AN  ANALYTICAL  COMPENDIUM  OF  THE  VARIOUS  BRANCHES 

OF  MEDICAL  SCIENCE  ;  for  the  Use  and  Examination  of  Students.  Second  edition,  revised 
and  improved.  In  one  very  large  and  handsomely  printed  royal  12mo.  volume,  of  over  one 
thousand  pages,  with  three  hundred  and  fifty  illustrations  on  wood.  Strongly  bound  in  leather, 
with  raised  bands.     (Extensively  used  by  students.) 

PREFACE  TO  THE  NEW  EDITION. 

The  speedy  sale  of  a  large  impression  of  this  work  has  afforded  to  the  authors  gratifying  evidence 
of  the  correctness  of  the  views  which  actuated  them  in  its  preparation.  In  meeting  the  demand 
for  a  second  edition,  they  have  therefore  been  desirous  to  render  it  more  worthy  of  the  favor  with 
which  it  has  been  received.  To  accomplish  this,  they  have  spared  neither  time  nor  labor  in  embo- 
dying in  it  such  discoveries  and  improvements  as  have  been  made  since  its  first  appearance,  and 
such  alterations  as  have  been  suggested  by  its  practical  use  in  the  class  and  examination-room. 
Considerable  modifications  have  thus  been  "introduced  throughout  all  the  departments  treated  of  in 
the  volume,  but  more  especially  in  the  portion  devoted  to  the  "  Practice  of  Medicine,"  which  has 
been  entirely  rearranged  and  rewritten.  The  authors  therefore  again  submit  their  work  to  the 
j)rof<3Ssion,  with  the  hope  that  their  efforts  may  tend,  however  humbly,  to  advance  the  great  cause 
of  medical  education. 

Notwithstanding  the  increased  size  and  improved  execution  of  this  work,  the  price  has  not  been 
increased,  and  it  is  confidently  presented  as  one  of  the  cheapest  volumes  now  before  the  profession. 


In  the  rapid  course  of  lectures,  where  Avork  for 
the  students  is  heavy,  and  review  necessary  for  an 
examination,  a  coinpend  is  not  only  valuable,  but 
it  is  almost  a  sine  qua  non.  The  one  before  us  is, 
in  most  of  the  divisions,  the  most  unexceptionable 
of  ail  books  of  the  kind  that  we  know  of.  The 
newest  and  soundest  doctrines  and  the  latest  im- 
provements and  discoveries  are  explicitly,  though 
concisely,  laid  before  the  student.  Of  course  itis 
useless  for  us  to  recommend  it  to  all  last  course 
students,  but  there  is  a  class  to  whom  we  verv 
sincerely  commend  this  cheap  book  as  worth  its 
weight  in  silver  —  that  class  is  the  graduates  in 
medicine  of  more  than  ten  years'' standing,  who 
have  not  studied  medicine  since.  They  will  perhaps 
find  out  from  it  that  the  science  is  not  exactly  now 
what  it  was  when  they  left  it  off. — The  Stethoscope 


Having  made  free  use  of  this  volume  m  our  ex- 
aminations of  pupils,  we  can  speak  from  experi- 
ence in  recommending  it  as  an  admirable  compend 
for  students,  and  as  especially  useful  to  preceptors 
who  examine  their  pupils.  It  will  save  the  teacher 
much  labor  by  enabling  him  readily  to  recall  all  of 
the  points  upon  which  his  pupils  should  be  ex- 
amined. A  work  of  this  sort  sliould  be  in  the  hands 
»f  every  one  who  takes  pupils  into  his  office  with  a 
viewof  examining  them;  and  this  is  unquestionably 
the  best  of  its  class.  Let  every  pracf  ilioner  who  has 
pupils  provide  himself  with  it,  and  he  will  find  the 
labor  of  refreshing  his  knowledge  so  much  facilitated 
that  he  will  be  able  to  do  justice  t()  his  pupilsat  very 
little  cost  of  time  or  trouble  to  himself.— Transyl- 
vania Med.  Journal. 


24 


BLANCHARD   &   LEA'S   MEDICAL 


A.,  8ic. 
THE    SKIN. 


In  one 


NELIGAN  (J.    MOORE),  M.  D.,  M.  R.  I 
A    PRACTICAL   TREATISE    ON   DISEASES    OF 

neat  royal  12mo.  volume,  of  334  pages.     {Just  Issued.) 

"We  know  of  no  other  treatise  on  this  interesting  I  The  greatest  value  of  Dr.  Neligan's  treatise  con- 
and  important  class  of  diseases  that  so  happily  meets  |  sists  in  the  plain  and  thoroughly  practical  exposition 
the  urgent  wants  of  the  great  mass  of  physicians.—  I  he  has  given  of  this  class  of  maladies.— £ri«.  and 
N.  Y.  Journal  of  Medicine.  \  For.  Med.-Ckirurg.  Review. 


PHILLIPS  (BENJAMIN),   F.  R.  S.,  &,c. 

SCROFULA;    its  Nature,  its  Prevalence,  its  Causes,  and  the  Principles  of  its 
Treatment.    In  one  volume,  octavo,  with  a  plate. 


PEREIRA  (JONATHAN),  M.  D.,  F.  R.  S.,  AND  L.  S. 
THE    ELE3IENTS    OP    MATERIA    MEDICA    AND    THERAPEUTICS. 

Third  American  edition,  enlarged  and  improved  by  the  author;  including  Notices  of  most  of  the 
Medicinal  Substances  in  use  in  ihe  civilized  world,  and  forming  an  Encyclopfedia  of  Materra 
Medica.  Edited  by  Joseph  Carson,  M.  D.,  Professor  of  Materia  Medica  and  Pharmacy  in  tha 
University  of  Pennsylvania.  In  two  very  large  octavo  volumes,  on  small  type,  with  about  four 
hundred  illustrations. 

Volume  I. — Lately  issued,  containing  the  Inorganic  Materia  Medica,  over  800  pages,  with  145 
illustrations. 

Volume  II. — Embracing  the  Organic  Materia  Medica,  was  left  by  the  late  author  in  nearly  a  com- 
plete state,  is  now  revising  with  his  MSS.,  by  Alfred  S.  Taylor  and  G.  Owen  Rees,  and  may 
be  expected  in  October  1853,  with  plates  and  several  hundred  wood-cuts. 

Tlie  present  edition  of  this  favorite  and  standard  worlc,  will  be  found  far  superior  to  its  predeces- 
sors. Besides  very  large  additions  and  alleralions  which  were  made  in  the  last  London  edition, 
the  work  has  undergone  a  thorough  revision  on  the  part  of  the  author  expressly  for  this  country  ; 
and  has  farther  received  numerous  additions  from  the  editor.  It  is  thus  greatly'  increased  in  size, 
and  most  completely  brought  up  to  the  present  state  of  our  knowledge  on  this  important  subject. 
A  similar  improvement  will  be  found  in  its  mechanical  execution,  being  printed  with  new  type  on 
fine  white  paper,  with  a  greatly  extended  series  of  illustrations,  engraved  in  the  highest  style  of  art. 


The  work,  in  its  present  shape,  and  so  far  as  can 
be  judged  from  the  portion  before  the  public,  forms 
the  most  comprehensive  and  complete  treatise  on 
materia  medica  extant  in  the  English  language. — 
Dr.  Pereira  has  been  at  great  pains  to  introduce 
into  his  work,  not  only  all  the  information  on  the 
natural,  chemical,  and  commercial  history  of  medi- 
cines, which  might  be  serviceable  to  the  physician 
and  surgeon,  but  whatever  might  enable  his  read- 
ers to  understand  thoroughly  the  mode  of  prepar- 


ing and  manufacturing  various  articles  employed 
either  for  preparing  medicines,  or  for  certain  pur- 
poses in  the  arts  connected  with  materia  medica 
and  the  practice  of  medicine.  The  accounts  of  the 
physiological  and  therapeutic  effects  of  remedies  are 
given  with  great  clearness  and  accuracy,  and  in  a 
manner  calculated  to  interest  as  well  as  instruct 
the  reader. — The  Edinburgh  Medical  and  Surgical 
Journal. 


PAGET  (JAMES),  F.  R.  S.,  AND  W.  S.  KIRKES. 
MANUAL   OF   PHYSIOLOGY.     Second  American  edition.     One  vol.,  large 

12mo.     (See  Kirkes.) 


PIRRIE  (WILLIAM),  F.  R.  S.  E., 

Professor  of  Surgery  in  the  University  of  Aberdeen. 

THE    PRINCIPLES   AND  PRACTICE   OF   SURGERY.     Edited  by  John 

Neill,  M.  D.,  Demonstrator  of  Anatomy  in  the  University  of  Pennsylvania,  Surgeon  to  the 
Pennsylvania  Hospital,  &c.  In  one  very  handsome  octavo  volume,  of  7^0  pages,  with  316  illus- 
trations.    (Just  Issued.) 


However  well  it  maybe  adapted  for  a  text-book 
(and  in  this  respect  it  may  compete  with  the  best  of 
them)  of  this  much  our  reading  has  convinced  us, 
that  as  a  systematic  treatise,  it  is  carefully  and  ably 
w^ritten,  and  can  hardly  fail  to  command  a  prominent 
position  in  the  library  of  practitioners;  though  not 
complete  in  the  fullest  sense  of  the  word,  it  never- 
tlieless  furnishes  the  student  and  practitioner  with 
as  chaste  and  concise  a  work  as  exists  in  our  Inn- 
guajje.  The  additions  to  the  volume  by  Dr.  Neill, 
are  judicious;  and  while  they  render  it  more  com- 
plete, greatly  enhance  its  practical  value,  as  a  work 
for  practitioners  and  students. — N.  Y.  Journal  of 
Medicine. 

We  know  of  no  other  surgical  work  of  a  reason- 
able size,  wherein  there  is  so  much  theory  and  prac- 
tice, or  where  subjects  are  more  soundly  or  clearly 
taught. — The  Stethoscope. 

There  is  scarcely  a  disease  of  the  bone  or  soft 
parts,  fracture,  or  dislocation,  that  is  not  illustrated 


by  accurate  wood-engravings.  Then,  again,  every 
instrument  employed  by  the  surgeon  is  thus  repre- 
sented. These  engravings  are  not  only  correct,  but 
really  beautiful,  showing  the  astonisliing  degree  of 
perfection  to  wliich  the  art  of  wood-engraving  has 
arrived.  Prof.  Pirrie,  in  the  work  before  us,  has 
elaborately  discussed  the  principles  of  surgery,  and 
a  safe  and  effectual  practice  predicated  upon  them. 
Perhaps  no  work  upon  this  subject  heretofore  issued 
is  so  full  upon  tlie  science  of  the  art  of  surger)'. — 
Nashville  Journal  of  Medicine  and  Surgery, 

We  have  made  ourselves  more  intimately  acquaint- 
ed with  its  details,  and  can  now  prcmounce  it  to  l>e 
one  of  the  best  treatises  on  surgery  in  tlie  English 
language.  In  conclusion,  we  very  strongly  recom- 
mend this  excellent  work,  both  to  the  practitioner 
and  student. — Catiada  Med.  Journal. 

Our  impression  is,  that  as  a  manual  for  students, 
Pirrie's  is  the  best  work  extant. — Western  Med.  and 
Surg.  Journal. 


AND   SCIENTIFIC    PUBLICATIONS. 


25 


RAMSBOTHAM  (FRANCIS  H.),   M.D. 
THE  PRINCIPLES  AND  PRACTICE  OF  OBSTETRIC  MEDICINE  AND 

SURGERY,  in  reference  to  the  Process  of  Parturition.  Sixth  American,  from  the  last  London 
edition.  Illustrated  with  one  hundred  and  forty-eight  Figures,  on  fifty-five  Lithographic  Plates. 
In  one  large  and  handsomely  printed  volume,  imperial  octavo,  with  520  pages. 

In  this  edition,  the  plates  have  all  been  redrawn,  and  the  text  carefully  read  and  corrected.     It 
is  therefore  presented  as  in  every  way  worthy  the  favor  with  which  it  has  so  long  been  received. 

From  Frof.  Hodge,  of  the  University  of  Pa. 
To  the  American  public,  it  is  most  valuable,  from  its  intrinsic  undoubted  excellence,  and  as  being 
"      ■      '  . -r  .T_-.-  u  ,.^.--,     w-  Its  circulation  will,  I  trust,  be  extensive  throughout 


tiie  best  authorized  exponent  of  British  Midwifery 
otir  country. 

.  We  recommend  the  student  who  desires  to  mas- 
ter this  difficult  subject  with  the  least  possible 
trouble,  to  possess  himself  at  once  of  a  copy  of  this 
work, — American  Journal  of  the  Med.  Sciences. 

It  stands  at  the  head  of  the  long  list  of  excellent 
obstetric  works  published  in  the  last  few  years  ia 
Great  I3ritain,  Ireland,  and  the  Continent  of  Eu- 
rope. We  consider  this  book  indispensable  to  the 
library  of  every  physician  engaged  in  the  practice 
of  midwifery. — Southern  Med.  and  Surg.  Journal. 


"When  the  M'-hole  profession  is  thus  unanimous 
in  placing  such  a  work  in  the  very  first  rank  us 
regards  the  extent  and  correctness  of  all  the  details 
of  the  theory  and  practice  of  so  important  a  branch 
of  learning,  our  commendation  or  condemnation 
would  be  of  little  consequence;  but  regarding  it 
as  the  most  useful  of  all  works  of  the  kind,  we 
think  it  but  an  act  of  justice  to  urge  its  claims 
upon  the  profession. — N.  O.  Med.  Journal. 


RIGBY  (EDWARD),   M.  D. 

Physician  to  the  General  Lying-in  Hospital,  &c. 

A   SYSTEM   OF   MIDWIFERY.     With   Notes  and   Additional   Illustrations. 

Second  American  Edition.     One  volume  octavo,  422  pages. 

The  repeated  demands  for  this  work,  which  has  now  for  some  time  been  out  of  print,  have  in- 
duced the  publishers  to  prepare  another  edition.  The  reputation  which  it  has  acquired  for  the 
clearness  of  its  views,  especially  as  regards  the  physiological  portion  of  obstetrical  science,  will 
)«>ecure  for  it  the  confidence  of  the  profession.  A  copy  of  the  first  edition  was  placed  in  the  hands 
of  the  late  Professor  Dewees,  a  few  weeks  before  his  death,  and  obtained  from  him  the  expressiou 
of  his  most  favorable  opinion. 


RICORD  (PH.),   M.  D. 

HUNTER  ON  VENEREAL,  with  extensive  Additions  by  Ricord.  (Nearly  Read i/.) 

See  Hunter. 


ROYLE  (J.  FORBES),  M.  D. 
MATERIA  MEDIC  A  AND  THERAPEUTICS ;  including  the  Preparations  of 

the  Pharmacopoeias  of  London,  Edinburgh,  Dublin,  and  of  the  United  States.  With  many  new 
medicines.  Edited  by  Joseph  Carson,  M.  D.,  Professor  of  Materia  Medica  and  Pharmacy  in 
the  University  of  Pennsylvania.  AVith  ninety-eight  illustrations.  In  one  large  octavo  volume, 
of  about  seven  hundred  pages. 

This  work  is,  indeed,  a  most  valuable  one,  and  I  ductions  on  the  other  extreme,  which  are  neces- 
will  fill  up  an  important  vacancy  that  existed  be-  |  sarily  imperfect  from  their  email  extent. — British 
tween  Dr.    Pereira's    most    learned  and   com^^letel  and  Foreign  Medical  Review. 
system  of  Materia  Medica,  and  the  class  of  pro-  | 


REESE  (G.  OWEN),  M.  D. 
ON  THE  ANALYSIS  OF  THE  BLOOD  AND  URINE  IN  HEALTH  AND 

DISEASE,  and  on  the  Treatment  of  Urinary  Diseases.,    Royal  r2mo.,  with  plates.     (See  Blood 
and  Urine,  Manuals  of.) 


RICORD  (P.),    M.  D. 

A  PRACTICAL  TREATISE  ON  VENEREAL  DISEASES.  With  a  Thera- 
peutical Summary  and  Special  Formulary.  Translated  by  Sidney  Doane,  M.  D.  Fourth  edition. 
One  volume,  octavo,  340  pages. 


SKE:y  (FREDERICK  C),   F.  R.  S.,  &c. 
OPERATIVE  SURGERY.     In  one  very  handsome  octavo  volume  of  over  G50 

pages,  with  about  one  hundred  wood-cuts. 

Its  literary  execution  is  superior  to  most  surgical 
treatises.  It  abounds  in  excellent  moral  hints,  and 
is  replete  with  original  surgical  expedients  and  sug- 
gestions.— Buffalo  Med.  and  Surg.  Journal. 

With  high  talents,  extensive  practice,  and  a  long 
experience,  Mr.  Skey  is  perhaps  competent  to  the 
task  of  writing  a  complete  work  on  operative  sur- 
gery.— Charleston  Med.  Journal. 


We  cannot  withhold  from  this  work  our  high  com- 
mendation. Students  and  practitioners  "will  find  it  an 
invaluable  teacher  and  guide  upon  every  topic  con- 
nected with  this  department.— A'.  Y.  Medical  Ga- 
zette. 

A  work  of  the  very  highest  importance — a  work 
by  itself.— Londow  Med.  Gazette. 


26 


BLANCHARD   &   LEA'S   MEDICAL 


SHARPEY   (WILLIAM),    M.D.,    QUAIN   (JONES),   M.  D.,   AND 
QUAIN   (RICHARD),    F.  R.  S.,  &.C. 

HUMAN  ANATOMY.     Revised,  with  Notes  and  Additions,  by  Joseph  Leidy, 

M.D.     Complete  in  two  large  oclavo  volumes,  of  about  thirteen  hundred  pages.    Beautifully 
illustrated  with  over  five  hundred  engravings  on  wood. 


It  is  indeed  n.  M'ork  cnlculated  to  make  an  era  in 
anatomical  study,  by  placing  before  the  student 
every  department  of  his  science,  with  a  view  to 
the  relative  importance  of  each  ;  and  so  skilfully 
have  the  different  parts  been  interwoven,  that  no 
one  who  makes  this  work  the  basis  of  his  studies, 
will  hereafter  have  any  excuse  for  nesrlecting  or 
undervaluing  any  important  particulars  connected 
with  the  structure  of  the  human  frame;  and 
whether  the  bias  of  his  mind  lead  him  in  a  more 
especial  manner  to  surgery,  physic,  or  physiology, 
he  will  find  here  a  work  at  once  so  comprehensive 
and  practical  as  to  defend  him  from  exclusiveness 
OH  the  one  hand,  and  pedantry  on  the  otlier. — 
Monthly  Journal  and  Retrospect  of  the  Medical 
Sciences. 


We  have  no  hesitation  in  recommending  this  trea- 
tise on  anatomy  as  the  most  complete  on  that  sub-  ■ 
ject  in  the  English  language;  and  the  only  one, 
perhaps,  in  any  language,  which  brings  the  state 
of  knowledge  forward  to  the  most  recent  disco- 
veries.— The  Edinburgh  Med.  and  Surg.  Journal. 

Admirably  calculated  to  fulfil  the  object  for  which 
it  is  intended. — Provincial  Medical  Journal. 

The  most  complete  Treatise  on  Anatomy  in  the 
English  language. — Edinburgh  Medical  Journal. 

There  is  no  work  in  the  English  language  to  be 
preferred  to  Dr.  Quain's  Elements  of  Anatomy. — 
London  Journal  of  Medicine. 


SMITH  (HENRY    H.),  M.  D.,  AND   HORNER  (W I  LLI  AM  E.),   M.  D. 

AN  ANATOMICAL  ATLAS,  illustrative  of  the  Structure  of  the  Human  Body. 

In  one  volume,  large  imperial  octavo,  with  about  six  hundred  and  fifty  beautiful  figures. 

With  the  view  of  extending  the  sale  of  this  beautifully  executed  and  complete  "Anatomical 
Atlas,"  the  publishers  have  prepared  a  new  edition,  printed  on  both  sides  of  the  page,  thus  mate- 
rially reducing  its  cost,  and  enabling  them  to  present  it  at  a  price  about  forty  per  cent,  lower  than 
former  editions,  while,  at  the  same  time,  the  execution  of  each  plate  is  in  no  respect  deteriorated, 
and  not  a  single  fi2:ure  is  omitted. 


These  figures  are  well  selected,  and  present  a 
ctnnplete  and  accurate  representation  of  that  won- 
derful fabric,  the  human  body.  The  plan  of  this 
Atlas,  which  renders  it  so  peculiarly  convenient 
for  the  student,  and  its  superb  artistical  execution, 
have  been  already  pointed  out.     We  must  congratu- 


late the  student  upon  the  completion  of  this  Atlas, 
as  it  is  the  most  C(mvenient  work  of  the  kind  that 
has  yet  appeared  ;  and  we  must  add.  the  very  beau- 
tiful manner  in  which  it  is  ''  got  up"  is  so  creditable 
to  the  country  as  to  be  flattering  to  our  national 
pride. — American  Medical  Journal. 


SARGENT  (F.  W.),   M.  D. 
ON  BANDAGING  AND  OTHER  POINTS   OF   MINOR  SURGERY. 

one  handsome  royal  12mo.  volume  of  nearly  400  pages,  with  128  wood-cuts. 

The  very  best  manual  of  Minor  Surgery  we  have 
seen  ;  an  American  volume,  with  nearly  four  hundred 
octavo  pages  of  good  practical  lessons,  illustrated 
by  about  one  hundred  and  thirty  wood-cuts.  In 
these  days  of  "  trial."  when  a  doctor's  reputation 
hangs  upon  a  close  hitch,  or  the  roll  of  a  bandage, 
it  would  be  well,  perhaps,  to  carry  such  a  journal  as 
Mr.  Sargent's  always  in  our  coat-pocket,  or,  at  all 
events,  to  listen  attentively  to  his  instructions  at 
home. — Buffalo  Med.  Journal. 


In 


We  have  carefully  examined  this  work,  and  find  it 
well  executed  and  admirably  adapted  to  the  use  of 
the  student.  Besides  the  subjects  usually  embraced 
in  works  on  Minor  Surgery,  there  is  a  short  chapter 
on  bathing,  another  on  ana;sthetic  agents,  and  an 
appendix  of  formulre.  The  author  has  given  an  ex- 
cellent work  on  this  subject,  and  his  publishers  have 
illuGtrated  and  printed  it  in  most  beautiful  style. — 
The  Charlest07i  Medical  Journal. 


In  one  volume,  octavo. 


STANLEY  (EDWARD). 
A  TREATISE  ON  DISEASES  OF  THE   BONES. 

extra  cloth,  286  pages. 

SMITH  (ROBERT  WILLIAM). 
A  TREATISE  ON  FRACTURES  IN  THE  VICINITY  OF  JOINTS,  AND 

ON  DISLOCATIONS.    One  volume  octavo,  with  200  beautiful  wood-cuts. 


SIMON   (JOHN),  F.  R.  S. 

GENERAL  PATHOLOGY,  as  conducive  to  the  Establishment  of  Rational 
Principles  for  the  Prevention  and  Cure  of  Disease.  A  Course  of  Lectures  delivered  at  St. 
Thomas's  Hospital  during  the  summer  Session  of  1850.  In  one  Beat  octavo  volume.  {Lately 
Issued.) 


His  views  are  plainly  and  concisely  stated,  and  in 
such  an  attractive  manner,  as  to  enchain  the  atten- 
tion of  the  reader,  and  should  they  be  adopted  by  the 
profession  at  large,  are  calculated  to  produce  im- 
l>ortant  changes  in  medicine.  Physicians  and  stu- 
dents will  obtain  from  its  perusal,  not  only  the  latest 


discoveries  in  Pathology,  but  that  which  is  evea 
more  valuable,  a  systematic  outline  for  the  prosecu- 
tion of  their  future  studies  and  investigations.  Alto- 
gether, we  look  upon  it  as  one  of  the  most  satisfactory 
and  rational  treatises  upon  that  branch  now  extant. 
— Medical  Ezajjiiner. 


SMITH  (TYLER  W.),   M.  D., 

Lecturer  on  Obstetrics  in  the  Hunterian  School  of  Medicine. 

ON   PARTURITION,    AND    THE    PRINCIPLES    AND    PRACTICE    OF 

OBSTETRICS.     In  one  large  duodecimo  vo  ume,  of  400  pages. 


AND    SCIENTIFIC    PUBLICATIONS. 


27 


SOLLY  (SAMUEL),   F.  R.  S. 
THE    HUMAN    BRAIN;    its  Structure,   Physiology,   and  Diseases.     With  a 
Description  of  the  Typical  Forms  of  the  Brain  in  the  Animal  Kingdom.    From  the  Second  and 
much  enlarged  London  edition.    In  one  octavo  volume,  with  120  wood-cuts. 


SCHOEDLER  (FRIEDRICH),   PH.D., 

Professor  of  the  Natural  Sciences  at  AVorms,  &c. 

THE  BOOK  OF  NATURE;  and  Elementary  Introduction  to  the  Sciences  of 
Physics,  Astronomy,  Chemistry,  Mineralogy,  Geology,  Botany,  Zoology,  andPhysiologv.  Trans- 
lated from  the  sixth  German  edition,  with  Additions,  by  Henry  Mkdlock,  F.  C.S.,&c.  And 
Additions  and  Alterations  by  the  American  Editor.  In  one  thick  volume,  small  oqiavo,  with  over 
600  illustrations  on  wood.     (Suitable  for  the  higher  Schools.) 


SMITH 
ANALYTICAL 


(F.  GURNEY),   M.  D.,  AND  JOHN    NEILL,   M.  D. 


COMPENDIUM    OF   THE   VARIOUS    BRANCHES    OF 

MEDICAL  SCIENCE.    One  vol.,  large  12mo.     (See  Neill.) 


TAYLOR  (ALFRED  S.),  M.  D.,  F.  R.  S., 

Lecturer  on  Medical  Jurisprudence  and  Chemistry  in  Guy's  Hospital. 

MEDICAL  JURISPRUDENCE.     Third  American,  from  the  fourth  and  improved 
English  Edition.    With  Notes  and  References  to  American  Decisions,  by  Edward  Haktshorne, 
M.  D.     In  one  large  octavo  volume,  of  about  seven  hundred  pages.     {Just  Ready.) 
In  the  preparation  of  the  English  edition,  from  which  this  has  been  printed,  the  author  has  found 
it  necessary  to  revise  the  whole  of  the  chapters,  as  well  as  to  make  numerous  alterations  and  addi- 
tions, together  with  references  to  many  recent  cases  of  importance.     A  Glossary  has  also  been 
added  for  the  convenience  of  those  whose  studies  have  not  been  directed  specially  to  this  subject. 
The  notes  of  the  American  editor  embrace  the  additions  formerly  made  by  Dr.  Griffith,  who  revised 
the  work  on  its  iirst  appearance  in  this  country,  together  with  such  new  matter  as  his  experience 
and  the  progress  of  the  science  have  shown  to  be  advisable.     The  work  may  therefore  be  regarded 
as  fully  on  a  level  with  the  most  recenj  discoveries,  and  worthy  of  the  reputation  which  it  has  ac- 
quired as  a  complete  and  compendious  guide  for  the  physician  and  lawyer. 


So  well  is  this  work  known  to  the  members  both 
of  the  medical  and  legal  professions,  and  so  higlily 
is  it  appreciated  l)y  them,  that  it  cannot  be  necessary 
for  us  to  say  a  word  in  its  commendation  ;  its  having 
already  reached  a  fourth  edition  being  the  best  pos- 
sible testimony  in  its  favor.  The  author  has  oh- 
viously  subjected  the  entire  work  to  a  very  careful 
revision.  We  find  scattered  through  it  numerous 
additions  and  alterations,  some  of  them  of  consider- 
able importance;  and  reference  is  made  to  a  large 
number  of  cases  which  have  occurred  since  the  date 
of  the  last  publication. — British  and  Foreign  Med.- 
Chirurg,  Review. 

The  fourth  edition  of  Dr.  Taylor's  INIanual  of 
Medical  Jurisprudence  needs  merely  a  simple  an- 
nouncement at  our  hands  ;  the  merits  of  the  work 
have  been  freely  canvassed  by  us  on  a  former  occa- 
sion, and  we  have  now  but  to  say  that  the  author 
has  spared  no  pains  in  keeping  it  on  a  par  in  all  re- 
spects with  the  advance  of  both  medical  and  legal 
science. — Dublin  Med.  Journal. 

This  work  of  Dr.  Taylor's  is  generally  acknow- 
ledged to  be  one  of  the  ablest  extant  on  the  subject 
of  medical  jurisprudence.  It  is  certainly  one  of  the 
most  attractive  books  that  we  have  met  with  ;  sup- 
plying BO  much  both  to  interest  and  instruct,  that 
we  do  not  hesitate  to  affirm  that  after  having  once 
commenced  its  perusal,  few  could  be  prevailed  upon 


to  desist  before  completing  it.  In  the  last  London 
edition,  all  the  newly  observed  and  accurately  re- 
corded facts  have  been  inserted,  including  much  that 
is  recent  of  Chemical,  Microscopical,  and  Patholo- 
gical research,  besides  papers  on  numerous  subjects 
never  before  published;  in  the  supervision  of  this, 
the  third  American,  one  of  the  last  labors  of  the  la- 
mented Dr.  Griffith,  we  find  a  goodly  number  of  notes 
and  additions.  The  publishers  deserve  the  support 
of  the  profession  for  the  publication  of  a  work  of 
such  sterling  merit. — Charleston  Medical  Journal 
and  Review. 

It  is  not  excess  of  praise  to  say  that  the  volume 
before  us  is  the  very  best  treatise  extant  on  Medical 
Jurisprudence.  In  saying  this,  we  do  not  wish  to 
be  understood  as  detracting  from  the  merits  of  the 
excellent  works  of  Beck,  Ryan,  Traill,  Guy,  and 
others;  but  in  interest  and  value  we  think  it  must 
be  conceded  that  Taylor  is  superior  to  anything  that 
has  preceded  it.  The  author  is  already  well  known 
to  the  profession  by  his  valuable  treatise  on  Poisons  ; 
and  the  present  volume  will  add  materially  to  his 
high  reputation  for  accurate  and  extensive  know- 
ledge and  discriminating  judgment,  Dr  Griffith  has. 
in  his  notes,  added  many  matters  of  interest  witli 
reference  to  American  Statute  Law,  &c.,  so  that  the 
work  is  brought  completely  up  to  the  wants  of  the 
physician  and  lawyer  at  tiie  present  day. — N.  W. 
Medical  and  Surgical  Journal. 


BY    THE    SAME    AUTHOR. 


ON  POISONS,  IN  RELATION  TO   MEDICAL  JURISPRUDENCE   AND 

MEDICINE.    Edited,  with  Notes  and  Additions,  by  R.  E.  Griffith,  M.  D.    In  one  large  octavo 
volume,  of  688  pages. 


The  most  elaborate  work  on  the  subject  that  our 
literature  possesses. — British  and  Foreign  Medico- 
Chirurgical  Revieio. 

It  contains  a  vast  body  of  facts,  which  embrace 
all  that  is  important  in  toxicology,  all  that  is 
necessary  to  the  guidance  of  the  medical  jurist,  and 
all  that  can  be  desired  by  the  .lawyer.  —  Medico- 
Chirurgical  Revieio. 


One  of  the  most  practical  and  trustworthy  works 
on  Poisons  in  our  language. — Western  Journal  of 
Medicine. 

It  is,  so  far  as  our  knowledge  extends,  incompa- 
rably the  best  upon  the  subject;  in  the  higliest  de- 
gree creditable  to  the  author,  entirely  trustworthy, 
and  indispensable  to  the  student  and  practitioner.— 
N.  Y.  Annalist. 


THOMSON  (A.  T.),  M.  D.,  F.  R.  S.,  &c. 
DOMESTIC  MANAGEMENT   OF   THE   SICK   ROO.M,  necessary  in  aid  of 

Medical  Treatment  for  the  Cure  of  Diseases.    Edited  by  R.  E.  Griffith,  M.  D.     In  one  large 
royal  12mo.  volume,  with  wood-cuts,  3G0  pages. 


BLANCHARD   &   LEA'S    MEDICAL 


TODD  (R.  B.),   M.  D.,  AND  BOWMAN  (WILLIAM),  F.  R.  S. 
PHYSIOLOaiCAL    ANATOMY   AND    PIIYSIOLOaY  OF   MAN.     With 

numerous  handsome  wood-cuts.    Parts  I,  II,  and  III,  in  one  octavo  volume,  552  pages.     Part  IV 

■will  complete  the  work. 

The  distinguishing  peculiarity  of  this  work  is,  that  the  authors  investigate  for  themselves  every 
fact  asserted ;  and  it  is  the  immense  labor  consequent  upon  the  vast  numl>er  of  observations  re- 
quisite to  carry  out  this  plan,  which  has  so  long  delayed  the  appearance  of  its  compielion.  Part 
IV,  with  numerous  original  illustrations,  is  now  appearing  in  the  Medical  News  and  Library  for 
1853.  Those  who  have  subscribed  since  the  appearance  of  the  preceding  portion  of  the  work  can 
have  the  three  parts  by  mail,  on  remittance  of  $2  50  to  the  publishers. 


TRANSACTIONS   OF    THE    AMERICAN    MEDICAL   ASSOCIATION. 

VOLUME  V,  for  1852,  large  8vo.,  of  940  pages,  with  numerous  maps. 

Also  to  be  had,  a  few  sets  of  the  Transactions  from  1848  to  1851,  in  four  large  octavo  volumes. 
These  volumes  are  published  by  and  sold  on  account  of  the  Association. 


WATSON   (THOMAS),    M.D.,    &c. 
LECTURES    ON    THE    PRINCIPLES    AND    PRACTICE    OF   PHYSIC. 

Third  American,  from  the  last  London  edition.    Revised,  with  Additions,  by  D.  Francis  Condie, 


M.  D  ,  author  of  a  "  Treatise  on  the  Diseases  of  Children,"  &c. 
eleven  hundred  large  pages,  strongly  bound  with  raised  bands. 


In  one  octavo  volume,  of  nearly 


To  sav  that  it  is  the  very  best  work  on  the  sub- 
ject now  extant,  is  but  to  echo  the  sentiment  of  the 
medical  press  throughout  the  country.  —  N.  O. 
Medical  Journal. 

Of  the  text-books  recently  republished  Watson  is 
very  justly  the  principal  favorite. — Holmes^s  Rep. 
to  Nat.  Med.  Assoc. 

By  universal  consent  the  work  ranks  among  the 
very  best  text-books  in  our  language. — Illinois  and 
Indiana  Med.  Journal. 

Regarded  on  all  hands  as  one  of  the  very  best,  if 
not  tlie  very  best,  systematic  treatise  on  practical 
medicine  extant. — St.  Louis  Med.  Journal. 


Confessedly  one  of  the  very  best  works  on  the 
principles  and  practice  of  physic  in  the  English  or 
any  other  language. — Med.  Examiner. 

Asa  text-book  it  has  no  equal;  as  a  compendium 
of  pathology  and  practice  no  superior. — New  York 
Annalist. 

We  know  of  no  work  better  calculated  for  being 
placed  in  the  hands  of  the  student,  and  for  a  text- 
book; on  every  important  point  the  author  seems 
to  have  posted  up  his  knowledge  to  the  day. — 
Amer.  Med.  Journal. 

One  of  the  most  practically  useful  books  that 
ever  was  presented  to  the  student.  —  N.  Y.  Mtd. 
Journal, 


WALSHE   (W.    H.),    M.  D., 

Professor  of  the  Principles  and  Practice  of  Medicine  in  University  College,  London. 

DISEASES    OF    THE    HEART,    LUNGS,    AND    APPENDAGES; 

Symptoms  and  Treatment.    In  one  handsome  volume,  large  royal  12mo.,  512  pages. 


their 


AVe  consider  this  as  the  ablest  work  in  the  En- 
glish language,  on  the  subject  of  winch  it  treats; 
the  author  being  the  first  stethoscopist  of  the  day. 
— Charleston  Medical  Journal. 

The  examination  we  have  given  the  above  work, 
convinces  us  that  it  is  a  complete  system  or  treatise 
upon  the  great  speciality  of  Physical  Diagnosis.  To 
give  the  reader  a  more  perfect  idea  of  what  it  con- 


tains, "we  should  be  glad  to  copy  the  whole  table  of 
contents  and  make  some  extracts  from  its  pages,  but 
our  limits  forbid.  We  have  no  hesitation  in  recom- 
mending the  work  as  one  of  the  most  complete  on 
this  subject  in  the  English  language;  and  yet  it  is 
not  so  voluminous  as  to  be  objectionable  on  this  ac- 
count, to  any  practitioner,  however  pressing  his 
engagements. — Ohio  Medical  and  Surgical  Journal. 


WHAT   TO   OBSERVE 
AT    THE    BEDSIDE    AND    AFTER   DEATH,    IN    MEDICAL    CASES. 

Published  under  the  authority  of  the  London  Society  for  Medical  Observation.     In  one  very 

hand.some  volume,  royal  r2mo.,  extra  cloth      {Just  Issued.) 

Did  not  the  perusal  of  the  work  justify  the  high 
opinion  we  have  of  it,  the  names  of  Dr.  Walshe,  the 
originator,  and  of  Dr.  Ballard,  as  the  editor  of  the 
volume,  would  almost  of  itself  have  satisfied  us  that 
it  abounds  in  minute  clinical  accuracy.  We  need 
not  say  that  the  execution  of  the  whole  reflects  the 
highest  credit  not  only  upon  the  gentlemen  men- 
tioned, but  upon  all  those  engaged  upon  its  produc- 
tion. In  conclusion,  we  are  convinced  that  the 
possession  of  the  work  will  be  almost  necessary  to 
every  member  of  the  profession — that  it  will  be 
found  indispensable  to  the  practical  physician,  the 
pathologist,  the  medical  jurist,  and  above  all  to  the 
medical  student. — London  Medical  Times. 

We  hail  the  appearance  of  this  book  as  the  grand 
desideratum. — Charleston  Medical  Journal. 

This  little  work,  if  carefully  read  by  even  old 
practitioners,  cannot  fail  to  be  productive  of  much 

?:ood  ;  as  a  guide  to  the  younger  members  of  the  pro- 
ession  in  directing  their  attention  specially  to  the 
best  mode  of  investigating  cases  so  as  to  arrive  at 


correct  diagnosis,  it  will  prove  exceedingly  valua- 
ble. The  great  difficulty  with  beginners,  who  have 
not  been  under  the  immediate  training  of  an  expe- 
rienced physician,  is  continually  found  to  be  in  the 
appreciation  of  the  true  condition  of  the  organs  and 
tissues.  Let  such  provide  themselves  with  this 
work  and  study  it  thoroughly,  and  they  will  find 
much  of  the  difficulty  removed. — Southern  Medical 
and  Surgical  Journal. 

This  is  truly  a  very  capital  book.  The  whole 
medical  world  will  reap  advantages  l>om  its  publi- 
cation. The  medical  journals  will  soon  show  its 
influence  on  the  character  of  the  •'  Reports  of  Cases" 
which  they  publish.  Drs.  Ballard  and  Walshe  have 
given  to  the  world,  through  a  small  but  useful 
medical  organization,  a  cheap  but  invaluable  book. 
We  do  advise  every  reader  of  this  notice  to  buy  it 
and  use  it.  Unless  he  is  so  vain  as  to  imagine  him- 
self superior  to  the  ordinary  human  capacity,  he  will 
in  six  months  see  its  inestimable  advantages. — 
Stethoscope. 


AND    SCIENTIFIC    PUBLICATIONS. 


29 


WILSON    (ERASMUS),  M.  D.,    F.  R.  S., 

Lecturer  on  Anatomy,  London. 

A  SYSTEM  OF  HUMAN  ANATOMY,  General  and  Special.  Fourth  Ameri- 
can, from  the  last  English  edition.  Edited  by  Paul  B.  Goddard,  A.  M.,  M.  D.  With  two  hun- 
dred and  fifty  illustrations.  Beautifully  printed,  in  one  large  octavo  volume,  of  nearly  six  hun- 
dred pages. 

In  many,  if  not  all  the  Colleges  of  the  Union,  it  i 
has  become  a  standard  text-book.  This,  of  itself,  I 
is  sufficiently  expressive  of  its  value.  A  work  very  j 
desirable  to  the  student;  one,  the  possession  of  i 
which  will  greatly  facilitate  his  progress  in  the  I 
study  of  Practical  Anatomy. — New  York  Journal  of  I 
Medicine.  \ 

Its  author  ranks  with  the  highest  on  Anatomy. —  | 
Southern  Medical  and  Surgical  Journal.  i 


It  offers  to  the  student  all  the  assistance  that  can 
be  expected  from  such  a  work. — Medical  Examiner. 

Tlie  most  complete  and  convenient  manual  for  the 
student  we  possess. — American  Journal  of  Medical 
Science. 

In  every  respect,  this  work  as  an  anatomical 
guide  for  the  student  and  practitioner,  merits  our 
warmest  and  most  decided  praise. — London  Medical 
Gazette. 


BY    THE    SAME   AUTHOR. 

THE  DISSECTOR;  or,  Practical  and  Surgical  Anatomy.  Modified  and  Re- 
arranged, by  Paul  Beck  Goddard,  M.  D.  A  new  edition,  with  Revisions  and  Additions.  In 
one  large  and  handsome  volume,  royal  12mo.,  with  one  hundred  and  fifteen  illustrations. 

In  passing  this  work  again  through  the  press,  the  editor  has  made  such  additions  and  improve- 
ments as  the  advance  of  anatomical  knowledge  has  rendered  necessary  to  maintain  the  work  in  the 
high  reputation  which  it  has  acquired  in  the  schools  of  the  United  Slates,  as  a  complete  and  faithful 
guide  to  the  student  of  practical  anatomy.  A  number  of  new  illustrations  have  been  added,  espe- 
cially in  the  portion  relating  to  the  complicated  anatomy  of  Hernia.  In  mechanical  execution  the 
work  will  be  found  superior  to  former  editions. 


BY   THE   SAME   AUTHOR. 

ON    DISEASES    OF   THE    SKIN.     Third  American,  from  the  third  London 

edition.     In  one  neat  octavo  volume,  of  about  five  hundred  pages,  extra  cloth.     (Just  Issued.) 

Also,  to  be  had  done  up  with  fifteen  beautiful  steel  plates,  of  which  eight  are  exquisitely  colored  ; 
representing  the  Normal  and  Pathological  Anatomy  of  the  Skin,  together  with  accurately  colored 
delineations  of  more  than  sixty  varieties  of  disease,  most  of  them  the  size  of  nature.  The  Plates 
are  also  for  sale  separate,  done  up  in  boards. 

The  increased  size  of  this  edition  is  sufficient  evidence  that  the  author  has  not  been  content 
■with  a  mere  republication,  but  has  endeavored  to  maintain  the  high  character  of  his  work  as  the 
standard  text-book  on  this  interesting  and  difficult  class  of  diseases.  He  has  thus  introduced  such 
new  matter  as  the  experience  of  the  last  three  or  four  years  has  suggested,  and  has  made  sucii 
alterations  as  the  progress  of  scientific  investigation  has  rendered  expedient.  The  illustralions  have 
also  been  materially  augmented,  the  number  of  plates  being  increased  from  eight  to  sixteen. 

The  "Diseases  of  the  Skin,"  by  Mr.  Erasmus 
Wilson,  may  n»w  be  regarded  as  the  standard  w^ork 
in  that  department  of  medical  literature.  The 
plates  by  which  this  edition  is  accompanied  leave 
nothing  to  be  desired,  so  far  as  excellence  of  delinea- 
tion and  perfect  accuracy  of  illustration  are  con- 
cerned.— Medico-C hirurgical  Review. 


As  a  practical  guide  to  the  classification,  diag- 
nosis, and  treatment  of  the  diseases  of  the  skin,  the 
book  IS  complete.  We  know  nothing,  considered 
in  this  aspect,  better  in  our  language ;  it  is  a  safe 
authority  on  all   the  ordinary   matters  which,  in 


this  range  of  diseases,  engage  the  practitioner's 
attention,  and  possesses  the  high  quality — unknown, 
we  believe,  to  every  older  manual — of  being  on  a 
level  with  science's  high-water  mark ;  a  sound  book 
of  practice. — London  Med.  Times. 

Of  these  plates  it  is  impossible  to  speak  too  highly. 
The  representations  of  the  various  forms  of  cuta- 
neous disease  are  singularly  accurate,  and  the  color- 
ing exceeds  almost  anything  we  have  met  wilh  in 
point  of  delicacy  and  finish. — British  and  Foreign 
Medical  Review. 


BY   THE   S.-VME   AUTHOR. 


ON    CONSTITUTIONAL    AND    HEREDITAaY    SYPHILIS,   AND    ON 

SYPHILITIC  ERUPTIONS.     In  one  small  octavo  volume,  beautifully  printed,  with  four  exqui- 
site colored  plates,  presenting  more  than  thirty  varieties  of  syphilitic  eruptions. 


This,  in  many  respects,  is  a  remarkable  work,  pre- 
senting views  of  theory  and  principles  of  practice 
which,  if  true,  must  change  completely  the  existing 
state  of  professional  opinion. — New  York  Journal  of 
Medicine. 

Dr.  Wilson's  views  on  the  general  subject  of 
Syphilis  appear  to  us  in  the  main  sound  and  judi- 
cious, and  we  commend  the  book  as  an  excellent 
monograph  on  the  subject.  Dr.  Wilson  has  pre- 
sented  us  a  very  faithful   and  lucid  description  of 


Syphilis  and  has  cleared  up  many  obscure  points  in 
connection  with  its  transmissihility,  pathology  and 
sequclne.  His  facts  and  references  will,  we  are  satis- 
fied, be  received  as  decisive,  in  regard  to  many 
questiones  vexatre.  They  appear  to  us  entitled  to 
notice  at  some  length.  We  have  perhaps  l)een  some- 
what prodigal  of  space  in  our  abstract  of  this  book. 
But  it  is  certainly  a  very  good  resume  of  received 
opinions  on  Syphilis,  and  presents,  to  many,  original 
and  striking  views  on  the  subject  — Med.  Examiner. 


WHITEHEAD  (JAMES),    F.  R.  C.  S.,    8lc. 
THE  CAUSES  AND  TREATMENT  OF  ABORTION   AND   STERILITY; 

being  the  Result  of  an  Extended  Practical  Inquiry  into  the  Physiological  and  Morbid  Conditions 
of  the  Uterus.    In  one  volume,  octavo,  368  pages. 


30  BLANCHARD    &    LEA'S    MEDICAL 


WILDE   (W.    R.), 

Surgeon  to  St.  Mark's  Ophthalmic  and  Aural  Hospital,  Dublin. 

AURAL  SURGERY,  AND  THE  NATURE  AND  TREATMENT  OF  DIS- 
EASES OF  THE  EAR.  In  one  handsome  octavo  volume,  with  illustrations.  {Just  Ready.) 
So  little  is  generally  know^n  in  this  country  concerning  ttie  causes,  symptoms,  and  treatment  of 
aural  affections,  Ihal  a  practical  and  scientific  Vi^ork  on  that  subject,  from  a  practitioner  of  Mr. 
Wilde's  great  experience,  cannot  fail  to  be  productive  of  much  benefit,  by  attracting  attention 
to  this  obscure  class  of  diseases,  v^^hich  too  frequently  escape  attention  until  past  relief.  The  im- 
mense number  of  cases  which  have  come  under  Mr.  Wilde's  observation  for  many  years,  have 
afforded  him  opportunities  rarely  enjoyed  for  investigating  this  branch  of  medical  science,  and  his 
work  may  therefore  be  regarded  as  of  the  highest  authority. 


WEST   (CHARLES),    M.  D., 

Senior  Physician  to  the  Royal  Infirmary  for  Children,  &c. 

LECTURES    ON   THE    DISEASES    OF  INFANCY  AND   CHILDHOOD. 

In  one  volume,  octavo,  of  four  hundred  and  fifty  pages. 

Every  portion  of  these  lectures  is  marked  byage- 


The  Lectures  of  Dr.  West,  originally  published  in 
the  London  Medical  Gazette,  form  a  most  valuable 
addition  to  this  branch  of  practical  medicine.  For 
many  years  physician  to  the  Children's  Infirmary, 
his  opportunities  for  observing  their  diseases  have 
been  most  extensive,  no  less  than  14,000  children 
having  been  brought  under  his  notice  during  the  past 
nine  years.  Tliese  have  evidently  been  studied  with 
great  care,  and  the  result  has  been  the  production  of 
the  very  best  work  in  our  language,  so  far  as  it  goes, 
on  the  diseases  of  this  class  of  our  patients.  The 
symptomatology  and  pathology  of  their  diseases  are 
especially  exhibited  most  clearly;  and  we  are  con- 
vinced that  no  one  can  read  with  care  these  lectures 
without  deriving  from  them  instruction  of  the  most 
important  kind. — Charleston  Med.  Journal. 


neral  accuracy  of  description,  and  by  the  soundness 
of  the  views  set  forth  in  relation  to  the  pathology 
and  therapeutics  of  the  several  maladies  treated  of. 
Tlie  lectures  on  the  diseases  of  the  respiratory  ap- 
paratus, about  one-third  of  the  whole  number,  are 
particularly  excellent,  forming  one  of  the  fullest 
and  most  able  accounts  of  tiiese  affections,  as  they 
present  themselves  during  infancy  and  childhood, 
in  the  English  language.  The  history  of  the  seve- 
ral forms  of  phthisis  during  these  periods  of  exist- 
ence, with  their  management,  will  be  read  by  all 
with  deep  interest. — the  American  Journal  of  the 
Medical  Sciences. 


WILLIAMS  (C.   J.  B.),    M.  D.,    F.  R.  S., 

Professor  of  Clinical  Medicine  in  University  College,  London,  &o. 

PRINCIPLES    OF   MEDICINE;   comprising  General  Pathology  and  Therapeu- 

tics,  and  a  brief  general  view  of  Etiology,  Nosology,  Semeiology,  Diagnosis,  Prognosis,  and 

Hygienics.    Edited,  with  Additions,  by  Meredith  Clymer,  M.  D.     Fourth  American,  from  the 

last  and  enlarged  London  edition.     In  one  octavo  volume,  of  nearly  five  hundred  pages.     Noiv 

Ready.     This  new  edition  has  been  materially  enlarged  and  brought  up  by  the  editor. 

It  possesses  the  strongest  claims  to  the  attention  of  the  medical  student  and  practitioner,  from 

the  admirable  manner  in  which  the  various  inquiries  in  the  different  branches  of  pathology  are 

investigated,  combined,  and  generalized  by  an  experienced  practical  physician,  and  directly  applied 

to  the  investigation  and  treatment  of  disease. — Editor's  Preface. 


The  best  exposition  in  our  language,  or,  we  be- 
lieve, in  any  language,  of  rational  medicine,  in  its 
present  improved  and  rapidly  improving  state. — 
British  and  Foreign  Medico-Chirurg,  Review. 


Few  books  have  proved  more  useful,  or  met  with 
a  more  ready  sale  than  this,  and  no  practitioner 
should  regard  his  library  as  complete  without  it. 
— Ohio  Med.  and  Surg.  Journal. 


BY  THE  SAME   AUTHOR, 

A  PRACTICAL  TREATISE   ON   DISEASES   OF  THE   RESPIRATORY 

ORGANS;  including  Diseases  of  the  Larynx,  Trachea,  Lungs,  and  Pleurae.     With  numerous 
Additions  and  Notes,  by  M.  Clymer,  M.  D.    With  wood-cuts.    In  one  octavo  volume,  pp.  508. 


YOUATT  (WILLIAM),  V.  S. 
THE    HORSE.      A  new  edition,  with  numerous  illustrations;    together  with  a 

general  history  of  the  Horse;  a  Dissertation  on  the  American  Trotting  Horse  ;  how  Trained  and 
.Jock-eyed ;  an  Account  of  his  Remarkable  Performances ;  and  an  Essay  on  the  Ass  and  the  Mule. 
By  J.  S.  Skinner,  formerly  Assistant  Postmaster-General,  and  Editor  of  the  Turf  Register. 
One  large  octavo  volume. 

BY   THE   SAME   AUTHOR. 

THE    DOa.     Edited  by  E.  J.  Lewis,  M.  D.     With  numerous  and  beautiful 

illustrations.    In  one  very  liandsome  volume,  crown  8vo.,  crimson  cloth,  gilt. 

ILLUSTRATED  MEDICAL  CATALOGUE. 

BLANCHARD  &  LEA  have  now  ready  a  Catalogiie  of  their  Medical  and  Surgical  Publi- 
cations, containing  descriptions  of  the  works,  with  Notices  of  the  Press,  and  specimens  of 
the  Illustrations,  making  a  pamphlet  of  forty-eight  large  octavo  pages.  It  has  been  prepared 
with  great  care,  and  without  regard  to  expense,  forming  one  of  the  most  beautiful  specimens 
of  typographical  execution  as  yet  issued  in  this  country.  Copies  will  be  sent  by  mail,  and 
the  postage  paid,  on  application  to  the  Publishers,  by  enclosing  a  three  cent  postage  stamp. 


AND   SCIENTIFIC    PUBLICATIONS. 


31 


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